Prions

Please note that other past theories about TSEs agents include :
• Nemavirus (Narang, 1990) : an enzyme-coding ssDNA surrounded by 2 protein layers (the inner one made up of PrP^c)
• Lentivirus
• virino (Dickinson and Outram, 1979) : a host protein (sinc) protects vDNA from the immune system
• To determine the mechanisms of intestinal transport of infection, and early pathogenesis, of sheep scrapie, isolated gut-loops were inoculated to ensure that significant concentrations of scrapie agent would come into direct contact with the relevant ileal structures (epithelial, lymphoreticular, and nervous). Gut loops were inoculated with a scrapie brain pool homogenate or normal brain or sucrose solution. After surgery, animals were necropsied at time points ranging from 15 min to 1 month and at clinical end point. Inoculum-associated prion protein (PrP) was detected by immunohistochemistry in villous lacteals and in sub-mucosal lymphatics from 15 min to 3.5 h post-challenge. It was also detected in association with dendritic-like cells in the draining lymph nodes at up to 24 h post-challenge. Replication of infection, as demonstrated by the accumulation of disease-associated forms of PrP in Peyer's patches, was detected at 30 days and sheep developed clinical signs of scrapie at 18-22 months post-challenge. These results indicate discrepancies between the routes of transportation of PrP from the inoculum and sites of de novo-generated disease-associated PrP subsequent to scrapie agent replication. When samples of homogenized inoculum were incubated with alimentary tract fluids in vitro, only trace amounts of protease-resistant PrP could be detected by western blotting, suggesting that the majority of both normal and abnormal PrP within the inoculum is readily digested by alimentary fluids. The study also suggests that the mechanism of resistance against these diseases does not operate at the level of gut absorption. The 50 sheep studied displayed different levels of resistance to scrapie, but all absorbed the prions equally readily. Although the study suggests that prion proteins can be absorbed by the gut, this seems to happen only rarely, at least in sheep. If the same is true of humans, then scientists may need to rethink exactly how the consumption of tainted meat leads to disease. Jeffrey's team predigested a mixture of abnormal PrP and typical sheep stomach contents. But when they then injected this into the gut, almost no rogue protein was absorbed, and subsequent testing found that the mixture contained almost no abnormal PrP. Sheep in the field are probably exposed to very little prion protein in their gut, because their stomachs would dispose of even the minuscule amounts ingested. Another possibility is that absorption occurs higher in the gut, before proteins are digested, perhaps in the mouth^{ref1, ref2}
Pathogenesis : according to such a theory, the CTD is essential in inducing the conformational switch (a-helix => b-fold) of the normal prion glycoprotein (PrP^c) into a disease-causing conformer (PrP^res / PrP^Sc) which aggregates into protease-resistant b-sheets. Host RNA molecules are cofactors for prion replication^ref. Induction of b-sheet structures in recombinant prion proteins is associated with increased solvent accessibility of tyrosine : antibodies directed against the prion protein repeat motif, tyrosine-tyrosine-arginine, recognize PrP^Sc but not the PrP^c isoform (antibody binding to the pathological can be created in vitro by partial denaturation of PrP^c). PrP contains 2 conserved N-glycosylation sites, which are partially occupied by a highly heterogeneous array of complex-type oligosaccharides carrying sialylated and fucosylated antennae. It has been proposed that the occupancy of the N-glycosylation sites can be correlated with differente strains of prions, but this hypothesis remains controversial. For example, prions isolated from the brains of patients with "classical" forms of CJD were found to have a very different sugar pattern from those isolated from patients with a variant form of CJD that struck some patients much earlier in life. But the sugar pattern of variant CJD prions was identical to those that cause BSE - a finding key to establishing that variant CJD was in fact the human form mad cow disease. Deletions of one or both glycosylation sites in transgenic mice result in unusual patterns of PrP^Sc deposition, suggesting that might play a role in the diseases process, but the functions of the sugars remain enigmatic. MALDI-MS molecular weight profiling of N-oligosaccharides released from hamster PrP and PrP^Sc revealed decreased amounts of oligosaccharides with bisecting GlcNAc residues, and increased amounts of tri- and tetraantennary sugars, in the PrP^Sc oligosaccharides compared with those from normal PrP. ES methodology, including ultrahigh-sensitivity MS/MS experiments on a Q-TOF instrument was used to provide detailed information on the occupancy of the second glycosylation site (Asn¹⁹⁶) of murine PrP, thus complementing a previous MS investigation of glycosylation at Asn¹⁸¹ in the hamster. The 2 sites are substituted with more than 60 bi-, tri-, and tetraantennary core-fucosylated structures, many of which are bisected. The oligosaccharides carry a limited number of antennae types. The diversity and difference in site occupancy arise largely from the arrangements of the antennae types in individual oligosaccharides. The NTD binds Cu⁺ preventing oxidative stress. It's the conversion process, not the accumulation of protein, that is key to the disease : depleting neuronal PrP in prion infection prevents disease and reverses spongiosis. The switch may produce a toxic by-product, an intermediate form, or may deplete a factor that is crucial to brain-cell survival^ref. Prnp^-/- animals don't have the disease and the gene loss itself don't create any syndrome : so it may be presumed that PrP^c has no importance in cell metabolism or its functions are substituted by PRND / prion protein 2 / dublet, which codes for doppel (as the latter has no NTD, Prnp^-/- animals suffer more from oxidative stress).
Inherited or new onset point mutations in the human PRNP gene, coding for p27-30^{CD230 / prion protein / PrPc}, may involve different codons, causing clinically different inherited diseases which can transmitted under appropriate circumstances. As the normal protein is usually expressed in Mammalia neurons (GPI-anchored), prions usually cause transmissible spongiform encephalopathies (TSE), without inflammation nor immune reaction
Some examples of species barrier in TSEs are the forms affecting :
• Antilocapra americana
• Tragelaphus strepsiceros
• Tragelaphus angasii
• chronic wasting disease (CWD)
• Cervus dama
• Cervus elaphus
• Odocoileus hemionus
• Odocoileus virginianus
• Mustela vison : transmissible mink encephalopathy (TME)
• Felis catus : feline spongiform encephalopathy (FSE)
• Ovis aries : scrapie
• Bos taurus : bovine spongiform encephalopathy (BSE) / mad-cow disease
• scientists currently have no idea whether Takifugu rubripes, Gallus gallus, turtles (Testudines) and frogs (Xenopus laevis), which also harbour prions, suffer diseases as a result. This is partly because they don't know what symptoms to look for.
Human diseases : 4 common PrP^Sc types have been found in humans to date: types 1-3 in sporadic and iatrogenic CJD, and type 4 associated exclusively with vCJD
• kuru

Epidemiology : the Fore tribe of Papua New Guinea between 1920s and 1950s. There are 4 major regions in Guinea - the coast is called Basse (low) or Maritime Guinea, the next section of the interior is called Moyenne (lesser) Guinea, the more mountainous area to the east is called Haute (high) Guinea, and the tail that drops down to the southeast is called Guinea Forestiere or Forest Guinea. These major division also provide broad cultural division as well - Basse Guinea is primarily Susu people and culture, Moyenne Guinea is more of the Pular people, who originate from nomadic tribes, Haute Guinea is primarily Malinke and Forest Guinea is home to the Toma, Kissi and similar groups who carry on strong traditional practices for medicine and religion. Its incidence has steadily fallen after the abrupt cessation of its route of transmission (endocannibalism) in Papua New Guinea in the 1950s. 11 patients with kuru were identified from July, 1996, to June, 2004, all living in the South Fore. All patients were born before the cessation of cannibalism in the late 1950s. The minimum estimated incubation periods ranged from 34 to 41 years. However, likely incubation periods in men ranged from 39 to 56 years and could have been up to 7 years longer. PRNP analysis showed that most patients with kuru were heterozygous (M/V) at polymorphic codon 129, a genotype associated with extended incubation periods and resistance to prion disease^ref.
Aetiology : cannibalistic funerary rituals (women and babies ate brains of died relatives) (Zigas, 1956; Gajdusek, 1957; Hadlow, 1959). The first in the population to develop kuru shared the genetic feature common to most vCJD victims, i.e. codon 129 (=>Met) homozygosis (dubbed M/M). In the UK, 66% of people are either heterozygous (M/V) or valine homozygous (V/V) and so, some believe, are less susceptible to prion disease. But some of those with M/V and V/V genotypes also developed kuru, often after incubation periods of 20 years or more : hence further cases of vCJD may show longer incubation periods and occur in older individuals with the M/V and V/V genotypes. There is extensive anthropological evidence that cannibalism is not just some rarity that happened in New Guinea : other evidence of prehistoric cannibalism includes cuts and burn marks on Neanderthal bones and biochemical analysis of fossilized human feces. A protective allele exists for both kuru and nvCJD : selection for this SNP has been very widespread or happened very early in the evolution of modern humans, before human beings spread all over the planet : we can't say which of those it is; but the obvious implication is that prion disease has provided the selection pressure.
Symptoms & signs : up to 30 years incubation => spinocerebellar ataxia, dysarthria, head, trunk and limbs tremors disappearing during sleeping => flaccid paralysis, dysphagia
Prognosis : death within 3-9 months. People in Papua New Guinea who once feasted on their own relatives succumbed to prion disease as much as half a century later, say scientists who have laboriously tracked down the last sufferers in remote villages. The discovery renews concerns that another prion disease, vCJD, might also be incubating silently and will only rear its head decades from now. Kuru caused an unprecedented epidemic in the Fore people of Papua New Guinea that peaked in the 1950s and early 1960s. Families steamed and ate the entire bodies of their relatives in a death ritual, unwittingly ingesting the infectious prion proteins that cause the debilitating neurological disease. But the practice stopped when it was prohibited by Australian authorities in the mid-1950s. Scientists' interest in kuru renewed with the realization that vCJD, transmitted from cows infected with BSE, might also cause an epidemic amongst those who ate infected beef in the 1980s and 1990s. So far, 156 vCJD deaths have been reported in Britain, the worst-affected country, and the number of new cases peaked in 2000, suggesting that the disease takes around 10 years to incubate. But there is still debate about the eventual size of the epidemic; no one knows whether many more are actually infected or for how many years they might incubate the disease before they show symptoms. Most people who had kuru in Papua New Guinea have already died, but the team ramped up existing disease monitoring in an attempt to find the last vestiges of the epidemic: those people who harboured the infectious prions for many years and are only just developing the disease. Working with local communities, they scoured isolated villages, which are typically located at mountainous altitudes above 2,000 metres, lost in dense, wet rainforest and often connected only by tracks. It's arduous trekking. From 1996 until mid-2004, the team found what they believe to be the final 11 remaining cases of kuru, which often manifests itself as problems with balance and coordination. The researchers also collected people's life histories to piece together when they were likely to have been infected. Because the cannibalistic ritual had stopped by 1960, the team calculated the incubation time as the time between 1960 and the year that a patient first exhibited kuru symptoms. This suggested an incubation lasting between 34 and 41 years, although the researchers did not know exactly when, before 1960, a person was infected. They then sought to obtain a more accurate estimate, based on the knowledge that boys stopped taking part in the cannibalistic ritual at around the age of seven. For their male patients, they therefore subtracted seven years from the age that they first showed symptoms. This gave a longest incubation time of 56 years, and perhaps up to 7 years longer, although the average incubation time is thought to be 12 years^ref. For the first time we can see the extraordinary incubation period in human prion disease. It's sobering that half a century on, this disease has not disappeared. vCJD could well have an average incubation time of 30 years or longer (more than the average for kuru) because the prions are passing from cows to humans rather than from human to human. This species barrier is known to extend incubation times in animal tests. The people who have already succumbed to vCJD could have been those with the shortest incubation period, perhaps because they were particularly genetically susceptible, as other evidence has suggested. Mathematical models used to predict the size of the likely vCJD epidemic could now take these findings into account. Most people seem to be thinking that we're over the worst of it. We have to be cautious about assuming this disease is going away.
Web resources :
• The National Creutzfeldt-Jakob Disease Surveillance Unit
• NINDS Kuru Information Page
• familial fatal insomnia (FFI) : an inherited prion disease, transmitted as an autosomal dominant trait, from mutations in codon 129 (=>Met) or 178 (Asp =>Asn)
• sporadic FFI
• familial FFI
Symptoms & signs : average age of insorgence is 49; atrophy of ventral and dorsomedial nuclei of the thalamus, various stages of cerebral ataxia and cerebellar ataxia, progressive insomnia, hallucinations, stupor, and coma; autonomic and motor disturbances are also present.
Prognosis : death within 6 months to 3 years of onset (average 13 months)
• Neumann familial progressive subcortical gliosis : proteinase K (PK)-resistant prion protein with no mutation in the coding region of the PRNP gene. Furthermore, the linkage to chromosome 17 suggests that genes other than the structural gene for prion protein on chromosome 20 are involved in prion metabolism.
• Huntington disease-like 1 (HDL1) : autosomal dominant in individuals heterozygous for a 192-nucleotide insertion within the coding region of the PRNP gene, resulting in an expanded prion protein with 8 extra octapeptide repeats.
• Gerstmann-Sträussler-Scheinker (GSS) syndrome : an inherited prion disease from mutations in codon 102 (Pro=>Leu), A117V, 178 (Asp=>Asn), 200 (Glu=>Lys), D202N, Q212P, Q217R, Q219. Variable amounts of smaller, distinct PrP^res isoforms of ca. 7-15 kDa are seen in all GSS variants

Epidemiology :
• UK : onset at age 50-60; deaths of definite and probable GSS cases :
• 1990 : 0 deaths
• 1991 : 0 deaths
• 1992 : 1 death
• 1993 : 2 deaths
• 1994 : 3 deaths
• 1995 : 3 deaths
• 1996 : 4 deaths
• 1997 : 1 death
• 1998 : 1 death
• 1999 : 0 deaths
• 2000 : 1 death
• 2001 : 2 deaths
• 2002 : 1 death
• 2003 : 2 deaths
• 2004 : 0 deaths
• 2005 : 4 deaths
• 2006 : 3 deaths
• USA : no confirmed cases since 1997
Symptoms & signs : common characteristics of cognitive and motor disturbances (cerebello-pyramidal syndrome) and the presence of multicentric amyloid plaques (AP) in the brain. 6 types exist :
• spongiform changes in GSS are related to the presence of high levels of these distinct 21-30 kDa isoforms (i.e. a subset of GSS P102L patients).
• ataxic form, there are progressive cerebellar ataxia and dementia
• telencephalic form, there are dysarthria, dementia, rigidity, tremor, and hyperreflexia
• GSS with neurofibrillary tangles (NFT), there are progressive short-term memory loss and clumsiness.
Prognosis : death occurs in 1 to 5 years.
• prion disease with protracted course : missense mutation in the PRNP gene (176640.0022)
• Creutzfeld-Jakob disease (CJD) : pulvinar atrophy. 0.25-2 cases per million inhabitants / year, expecially between age 55 and 75. 993 people have died of all forms of CJD in Britain between 1990 and 2004. Some 740 of those deaths were attributed to sporadic CJD, the most common form of the disease
• classical CJD (first described in 1920; average age of diagnosis : 68 years (can be manifested in infancy^ref); average duration of disease after diagnosis : 6.5 months)
• sporadic CJD (sCJD) (85-90%) : 117 (Ala=>Val), 178 (Asp=>Asn), 198 (Phe=>Ser), 200 or 210.
• Heidenhain's syndrome or variant : a rapidly progressive degenerative disease

Aetiology : methionine homozygosity at codon 129 and "type 1" protease-resistant prion protein, spongiform encephalopathy
Symptoms & signs : beginning and causing the most pronounced damage in the right occipital lobe, manifested by cortical blindness (=> atrophy of the visual cortex => bilateral inferior hemianopsia), presenile dementia, dysarthria, ataxia, athetoid movements, and generalized rigidity, but less damage in the cingulate gyrus and basal ganglia compared with patients with CJD who have cerebral ataxia as the leading clinical sign. The CSF assay for the 14-3-3 protein may be normal. Disease course : 5.7 months
• myoclonic variant : methionine homozygosity at codon 129 and to "type 1" protease-resistant prion protein
• variant with dementia of long duration : different genotypes at codon 129 and "type 2" protease-resistant prion protein.
• ataxic variant : different genotypes at codon 129 and "type 2" protease-resistant prion protein.
• variant with kuru plaques : different genotypes at codon 129 and "type 2" protease-resistant prion protein
Epidemiology : prevalence : 1 every 1,000,000
• UK : deaths of definite and probable sporadic CJD cases
• 1990 : 28 deaths
• 1991 : 32 deaths
• 1992 : 45 deaths
• 1993 : 37 deaths
• 1994 : 53 deaths
• 1995 : 35 deaths
• 1996 : 40 deaths
• 1997 : 60 deaths
• 1998 : 63 deaths
• 1999 : 62 deaths
• 2000 : 49 deaths
• 2001 : 56 deaths
• 2002 : 73 deaths
• 2003 : 58 deaths
• 2004 : 1 death
• 2005 : 122 cases, 64 deaths
• 2006 : 87 cases, 48 deaths
• USA : 1024 deaths
• 1997 : 54 deaths
• 1998 : 44 deaths
• 1999 : 65 deaths
• 2000 : 97 deaths
• 2001 : 138 deaths
• 2002 : 127 deaths
• 2003 : 142 deaths
• 2004 : 167 deaths
• 2005 : 144 (1 per million cases, compared with 2 cases per million in the UK during the same period)
• 8 Nov 2006 : 46 deaths
The decrease in referrals is however potentially concerning from the point of view of complete case ascertainment. The reason for this drop is unknown and the numbers will need careful monitoring over 2005. It is particularly notable that the number of recorded sporadic CJD deaths in 2004 is lower than in the 3 previous years; however, the death data for 2004 may be incomplete. Detailed clinical and epidemiological information has been obtained for the great majority of patients. The case-control study for risk factors of CJD has continued and initial analysis has been undertaken. The post mortem rate for patients with suspected CJD is high, although there is ongoing evidence that this rate continues to decline, in line with general autopsy rates in the UK. This is reflected in the reduced number of brain specimens examined in the neuropathology laboratory in 2004. The reduction in sporadic CJD numbers (32 in 2004, 52 in 2003) is another potential concern along with the fall in referral numbers and sporadic CJD deaths noted above. In 1990-2003 mortality rates from sporadic CJD in England, Scotland, Wales and Northern Ireland were, respectively, 0.86, 0.84, 1.08 and 0.57/million/year. The difference between the rates in each country is not statistically significant (p>0.2). These rates are comparable to those observed in other countries in Europe and elsewhere in the world, including countries which are free of BSE. There was some variation in the observed mortality rates between the different regions within the UK but this variation is not statistically significant (p>0.2). The highest and lowest mortality rates from sporadic CJD were observed in the South West (SMR=129) and Northern Ireland (SMR=79).
Only about 3-4 cases appear in New Zealand and 300 cases in the USA each year (30 under age 55 and 270 above age 55), but several studies have suggested that the disorder might be more common than thought and that as many as tens of thousands of cases might be going unrecognized. First and foremost, CJD is not a nationally reportable disease. Even with nationally reportable diseases, one sees significant under-reporting, probably related to the health care delivery system in the USA, which is heavily weighted towards private-sector providers. Unfortunately the private sector is less consistent with disease reporting to state and federal levels. In the absence of a national mandate for reporting of a disease, the incentive becomes negligible, so the traditional "tip of the iceberg" seen in disease reporting shrinks even further. Clusters of sporadic CJD have been reported in various areas of the United States -- Pennsylvania in 1993, Florida in 1994, Oregon in 1996, New York in 1999-2000, and Texas in 1996. In addition, several people in New Jersey developed CJD in recent years, including a 56-year-old woman who died on 31 May 2003. Although in some instances, a BSE link was suspected, all of the cases ultimately were classified as sporadic CJD. Researchers at Yale University, who conducted a 1989 study that found 13% of Alzheimer's disease patients actually had CJD^ref. Although autopsies once were performed on approximately 50% of all corpses, the frequency has dropped to < 15% in the United States. The National Center for Health Statistics (NCHS) -- a branch of the CDC -- stopped collecting autopsy data in 1995. While autopsies have been declining, the number of deaths attributed to Alzheimer's has increased more than 50-fold since 1979, going from 857 deaths then to nearly 50 000 in 2000, partly due to the aging of the population. Switzerland discovered in 2002 that its CJD rate was twice that of any other country in the world. Switzerland had been seeing 8 to 11 cases per year from 1997 to 2000. Then the incidence more than doubled, to 19 cases in 2001 and 18 cases in 2002. In the 18-year period between 1979 and 1996 USA saw a jump from 1 case of sporadic CJD in people under the age of 30 (a warning sign for vCJD) to 5 cases in 5 years between 1997 and 2001. There have been increases in sporadic CJD in France, Germany, and Italy, all of which have detected mad cow disease in their cattle. PrP^Sc is deposited in the neuroepithelium of the olfactory mucosa in patients with sporadic CJD, and olfactory biopsy may provide diagnostic information in living patients. The olfactory pathway may represent a route of infection and a means of spreading prions.
Human remains in cattle feed could have caused the first case of mad cow disease. The hypothesis seeks to answer lingering questions about the fatal infection, which has affected 180,000 cows in Britain alone since the mid-1980s, and has gone on to cause > 100 deaths in humans. During the 1960s and 1970s Britain imported hundreds of thousands of tonnes of whole and crushed bones and animal carcasses. These were used for fertilizer and to feed livestock. Nearly 50% of these imports came from Bangladesh, where peasants gathering animal materials may have also picked up human remains. Other experts in the field view the idea with scepticism, saying that proof remains circumstantial. The argument isn't very compelling because there's no smoking gun evidence. Yet until 1986 no such illness had been spotted in cattle. Once recognized, BSE became widely known as 'mad cow disease'. The incidence of the disease then rocketed, peaking in late 1992. Tests indicated misshapen prion proteins in the brains of the cows as the source of the problem. And when authorities banned the practice of recycling animal remains into cattle feed the number of sick livestock began to drop. But experts continue to puzzle over how BSE arose in the first place. One of the most widely believed theories is that prions responsible for sheep scrapie got incorporated into cattle feed. Scientists argue that ingested scrapie prions radically altered the normal, analogous proteins in one cow, which then developed the first case of BSE.  But the Colchesters point out that cows have been exposed to scrapie for 70 years, so it is hard to explain why BSE emerged only recently. A more likely source is recent exposure to human remains carrying sporadic CJD. Religious customs in Bangladesh and surrounding areas mean that many corpses are disposed of in rivers. Nearly 50 per cent came from Bangladesh, India, and Pakistan, where gathering large bones and carcasses from the countryside and from rivers is an established local trade. Hindu funerary practices require that human remains are disposed of in a river, preferably the Ganges. Although the body should ideally be burned, many people cannot afford enough wood for a full cremation, the report's authors claim. Simply smoking the pelvis in women and the torso in men is sometimes enough. And many complete corpses are thrown into the Ganges. Human remains have been described in material delivered to processing mills. And during the 1960s, human material was confirmed in consignments of bones shipped into French docks from Asia.People may have collected remnants from such bodies when foraging for animal carcasses^ref. Any prions in these corpses might then have caused mad cow disease. Experts agree that the theory needs to be checked. More information needs to be collected about the number of deaths from sCJD in the Indian subcontinent (about 120 Hindu people each year : but the poor, who might account for many corpses in the Ganges, also have a relatively short life expectancy, while human prion diseases, meanwhile, often present themselves in old age), what happened to the bodies, and whether prions could have been transmitted in the way proposed. When human sporadic CJD prions were injected into mice in previous studies, the mice did not become ill^ref. The paper includes an overview of the various theories on the origin of BSE, namely:
• extrinsic origin (acquired from another species):
• human TSE
• sheep scrapie
• other species (such as farm, zoo, game, or wild animal)
• iatrogenic: contaminated medication transmitting TSE from another animal (including human).
• intrinsic origin (spontaneous event within one or more individual animals)
• predisposing factors (factors that could predispose to an extrinsic or intrinsic mechanism)
• host factors
• organophosphate pesticide exposure; high manganese or low copper levels in soil, Acinetobacter bacteria in cattle feed.
For the opinion of the Eu Scientific Steering Committee, Nov 2001, "Hypotheses on The Origin and Transmission of BSE". Readers might be reminded that the inclusion of human tissue in recycled animal feed was first discussed in April 1996, when a Swiss television program, investigating the links between contaminated animal feed and BSE, discovered that thousands of human placentas from hospitals in Switzerland had been turned into animal feed since the 1960s. Subsequently, the City council of Zurich launched an inquiry into how such a practice, which breached hospital guidelines on waste disposal, could remain undetected for so long. The department of health and environment in Zurich indicated that they had evidence that 820 kilograms of human placentas from 2 hospitals in Zurich were mixed in with dead pets and turned into animal feed since the start of 1995. They added the same disposal route was certainly used by hospitals in Winterthur and probably by hospitals in other Swiss cities^ref. It was further reported that the Zurich canton veterinarian pledged to stop the practice immediately and to consider prosecutions and that the feed producer had to destroy 200 tons of MBMs in stock. Was Switzerland the only country where such or similar practice prevailed?
Prognosis : average survival < 6 months
• familial CJD (5-10%) : 129 (=>Val)

Epidemiology :
• UK : deaths of definite and probable familial CJD cases
• 1990 : 0 deaths
• 1991 : 3 deaths
• 1992 : 5 deaths
• 1993 : 3 deaths
• 1994 : 4 deaths
• 1995 : 2 deaths
• 1996 : 2 deaths
• 1997 : 4 deaths
• 1998 : 4 deaths
• 1999 : 2 deaths
• 2000 : 2 deaths
• 2001 : 3 deaths
• 2002 : 4 deaths
• 2003 : 1 deaths
• 2004 : 0 deaths
• 2005 : 6 deaths
• 2006 : 4 deaths
• USA : 184 deaths
• 1997 : 6 deaths
• 1998 : 6 deaths
• 1999 : 9 deaths
• 2000 : 12 deaths
• 2001 : 16 deaths
• 2002 : 22 deaths
• 2003 : 45 deaths
• 2004 : 21 deaths
• 2005 : 39 deaths
• 2006, Nov 8 : 8 deaths
• iatrogenic CJD (< 1%) due to use of contaminated surgical equipments. The risk of contracting CJD from surgery is very low :
• neurosurgery (the greatest risk) : CNS
• cornea allotransplants
• dura mater allotransplants
• Tutoplast^® [Pfrimmer-Viggo GmbH & Co., Erlangen, Germany]
• Lyodura^® [Braun Melsungen AG, Melsungen, Germany] :
• Japan : on 1997, a nongovernment surveillance group for CJD in Japan reported 43 cases of CJD associated with receipt of cadaveric dura mater grafts. In all but one case, the most probable vehicle of transmission was a single brand of dural graft produced before May 1987. The precise number of dura mater grafts used in Japan is unknown, but an estimated 20,000 grafts per year might have been used during 1983 to 1987, when the manufacturer revised collection and processing procedures for the implicated product to reduce the risk for CJD transmission. As of March 2003, ongoing surveillance in Japan had identified an additional 54 dura mater graft-associated cases. All 97 patients received dura mater grafts during the period 1978 to 1991. 3 patients received more than one dural graft during this period, including one patient reported previously : in all 3 cases, the first graft was considered to be the source of infection. Medical conditions leading to the use of dural grafts in these patients included tumor (n = 46), brain hemorrhage (n = 14), Jannetta procedure for facial palsy (n = 13) and for trigeminal neuralgia (n = 6), intracranial aneurysm (n = 8), unspecified anomalies (n = 5), intracranial hematoma (n = 3), injury (n = 1), and ossification of the spinal posterior longitudinal ligament (n = 1). Latency periods ranged from 14 months (receipt in 1987 and onset in 1989) to 275 months (receipt in 1978 and onset in 2001). The median and mean latency periods were 122 and 125 months, respectively. During 1983 to 1987, the estimated minimum risk for CJD within 17 years of receipt of the implicated product in Japan was approximately 1 case per 1250 grafts (0.04%). No cases have been reported among patients who received their first dural graft after 1991; however, because of the long latency period between graft placement and symptom onset, additional cases of graft-associated CJD are likely to be reported. That all Lyodura^®-associated CJD cases to date occurred among patients who received grafts before 1992 suggests that all implicated grafts likely were processed before 1987; the implicated product's expiration date is 5 years after processing. In 1997, the report of 43 cases of dura mater graft-associated CJD in Japan represented the largest cluster of such cases in any one country. In one of the CJD cases reported in Japan, the implicated graft was used in a spinal (not an intracranial) procedure : this case suggests that transmission from contaminated dura might occur in areas of the neuraxis outside of the cranial vault. Subsequently, numerous other dura mater graft-associated cases were identified worldwide; nearly all patients had received the implicated product, including one additional U.S. patient
• USA : Lyodura^® never was produced by the manufacturer for distribution in the USA, and relatively few Lyodura^® grafts were used in this country. In May 1987, after identification of the first dural graft-associated CJD case in a 28-year-old U.S. woman from Connecticut who had received the implicated product 2 years before, the manufacturer revised its procedures for collecting and processing dura mater grafts to reduce the risk for CJD transmission (e.g., by discontinuing the commingling of dura and disinfecting them with sodium hydroxide). B.Braun Melsungen, its Japanese distributor, and the Japanese health ministry were later ordered by the courts to pay out £330,000 to the families of CJD victims in Japan, which had the largest Lyodura-associated outbreak. In 1997, an estimated 4500 dural grafts were distributed for use in the USA. After the TSEAC recommendations were issued, the number of dural grafts distributed for use in the United States declined to an estimated 900 grafts in 2002.
• Australia : Lyodura was introduced in 1972 and withdrawn in 1987, when the product was found to be linked to non-variant CJD. It was also used in Australia during the 1970s and 1980s : Australians who received the product had a 0.23% chance of contracting the disease.
• UK : a 34-year-old man (Simon Stratford) died of CJD > 15 years after an operation in which he was treated with infected Lyodura graft. The father-of-4 from St Neots, Cambridgeshire, needed a repair to his dura mater, a membrane lining between the skull and the brain, when he had a tumour removed at the Neurosurgery Department of Addenbrooke's Western General Hospital, Cambridge, in September 1987. Between October 2002 and April 2003, Mr Stratford had problems sleeping, then lost feeling in his face and arm, and became withdrawn and angry as his condition deteriorated, losing his ability to swallow, walk and speak. Up to 50 former hospital patients in Edinburgh are feared to be at risk of having contracted the human form of mad cow disease during brain surgery. The graft was withdrawn from the market in 1996 ago after it was linked with CJD. But NHS Lothian health bosses have warned that tracing the affected patients will not be possible as case notes were not stored. In Edinburgh, 4-5 patients per year may have had this material used. Many of the notes of these patients have been destroyed so it will make it impossible to know whether this was used. An intelligent guess might be made from the nature of the operation and the research. 3 of the surgeons from Edinburgh who are believed to have used the material retired in 1987, which could add further difficulties to assessing the extent of the problem. Experts will be forced to make only an "intelligent guess" over whether or not people were exposed to any danger. The risk of contamination from Lyodura grafts in the city is thought to stretch between 1982 and 1992 when the product was widely used. Lyodura, was withdrawn from the market 9 years ago following links with CJD.
Recipients of contaminated dura mater grafts might remain at risk for CJD for >22 years after receiving grafts. Patients with a rapidly progressive dementia consistent with CJD and a history of dural graft implantation should be reported through local or state health departments to CDC.
• administration of human-derived GH
• tonsils (see below)
• spleen (33%)
• appendix
• muscles (25%)^ref, may also harbor prions and contaminate surgical instruments
• liver transplantation or the associated albumin transfusions^ref
Surgical incidents occur when instruments that are considered potentially contaminated with the CJD agent during use on an index patient have been subsequently re-used on other patients. 183 surgical incidents were reported to the Panel during its first 4 years :
• sporadic CJD (possible, probable or definite) / 86 (47%)
• variant CJD (possible, probable or definite) / 61 (28%)
• other types of CJD, or 'at risk' of CJD, or CJD type unclear / 34 (19%)
• not CJD / 12 (7%)
Surgical incidents often involve a number of procedures from different specialties :
• gastroenterology / 68 (18%)
• obstetrics and gynaecology / 27 (7%)
• neurology/neurosurgery / 27 (7%)
• orthopaedics / 40 (11%)
• ophthalmology / 28 (8%)
• ear nose and throat / 26 (7%)
• dentistry /  28 (8%) : the UK Health Protection Agency (HPA) will use mice to see if vCJD can be passed on from contaminated dental instruments. They will also see if the mice show signs of the disease in the tissue in their mouths. The risk is thought to be small, but comes after concerns vCJD could be spread via donated blood and tissue. The government has taken measures to protect the blood supply by banning donations from certain groups, including those who have had blood transfusions since 1980, after it emerged 2 people may have been infected after having a blood transfusion. There have also been concerns about whether the prions responsible for vCJD can be spread by surgical instruments, especially when used during brain surgery. The aim of the 3-year experiment is to give the Department of Health more guidance on the risks posed by vCJD in dentistry and to determine whether stricter advice on the best cleaning methods needs to be issued. The study was outlined at the HPA's 2005 conference at the University of Warwick, which heard an estimated 75 million dental procedures are conducted in the UK each year and 2 million of these are invasive root canal treatments. Experts will also look at the different methods of decontaminating surgical instruments, such as manual scrubbing, the use of sound waves and washer disinfection
• other / 122 (34%)
• total /  364 (100%)
Investigation of past surgical incidents occasionally resulted in advice to remove from surgical use on patients other than the index patient (to quarantine or destroy, or donate for research) instruments considered to be potentially contaminated with the CJD agent. Such advice was generally only given for instruments that had not undergone > 10 cycles of use and decontamination since their use on certain index patients. During the last reporting year (year 4, 2003-2004) the Panel advised that instruments be removed from use on other patients following use on an index patient with, or at-risk of, CJD in 2 incidents. For reports to 31 Aug 2004, advice has been given to contact and inform 7 patients who were involved in 10 surgical incidents of their potential exposure to CJD via surgical instruments. Such advice was generally only given for patients who were definitely exposed to potentially contaminated instruments immediately after the instruments had been used on certain index patients. It was advised that these patients should be considered to be potentially at risk of CJD for public health purposes and asked to take certain precautions (i.e. not to donate blood or other tissues, and to inform their medical and dental carers prior to any invasive procedures) in order to reduce the potential risk of onward transmission of the CJD agent by possible
iatrogenic routes.
Patients with extraneural PrP^Sc had a significantly longer duration of disease and were more likely to have uncommon molecular variants of sporadic CJD than were patients without extraneural PrP^Sc. Among the patients registered by the end of 2000 the frequency of methionine-methionine (MM) genotype was much lower in the UK (4%, 1 of 27 cases) than in France (62%, 48 of 77, p=0.0001) : different genotypic distributions of hGH-transmitted CJD in French and UK patients may be due to infection with different contaminating strains of the CJD agent in France and the UK. hGH-transmitted CJD homozygous cases in France (of which 74% (48 of 65) were MM) arose significantly earlier than in heterozygous cases
Prevention : surgical instruments used on people who are known to have CJD are quarantineed after use, and then destroyed
• an enzyme from bacteria found in volcanic pools digests the prions when exposed to a solution with a temperature of 60°C, reducing their infectivity almost a million-fold
• decontamination of surgical instruments by using radio-frequency gas-plasma treatment^ref
Epidemiology :
• UK : deaths of definite and probable iatrogenic CJD cases
• 1990 : 5 deaths
• 1991 : 1 death
• 1992 : 2 deaths
• 1993 : 4 deaths
• 1994 : 1 death
• 1995 : 2 deaths
• 1996 : 4 deaths
• 1997 : 6 deaths
• 1998 : 3 deaths
• 1999 : 6 deaths
• 2000 : 1 death
• 2001 : 3 deaths
• 2002 : 0 deaths
• 2003 : 4 deaths
• 2004 : 0 deaths
• 2005 : 3 deaths
• 2006 : 1 death
• USA : 5
• 1997 : 0
• 1998 : 1
• 1999 : 0
• 2000 : 2
• 2001 : 0
• 2002 : 1
• 2003 : 1
• 2004 : 0
• 2005 : 0
• 2006 : 0
• new variant CJD (vCJD / nvCJD) was first recognized in a British 19-year-old boy who died in 1995

It has infectious aetiology via...
• oral route from :
• specified risk material (SRM) from cattle (Bos taurus) affected with BSE : in 1996 the human PrP^Sc was found to resemble the PrP^Sc found in BSE. The Committee for Proprietary Medical Products (CPMP) of the European Agency for the Evaluation of Medicinal Products (EMEA) established, in 2001, 4 BSE risk categories on the basis of examinations of cows and other animals that became infected with similar diseases (for example, sheep which contracted scrapie). These categories have been summarized in the "Note for guidance on minimizing the risk of transmitting animal spongiform encephalopathy agents via medicinal products," as follows :
• category I (very high infectivity):
• brain
• spinal cord
• eyes
• category II (high infectivity):
• cerebrospinal fluid
• hypophysis (pituitary gland)
• ilium (lower part of the small intestine)
• lymph nodes
• tonsils
• spleen
• suprarenal gland (e.g. from the peripheral nerve tissue and the suprarenal gland of the BSE positive 94 month old cow that had died on 9 Mar 2004^ref.)
• upper part of the colon (proximal)
• dura mater ("hard" meninges)
• placenta
• pineal gland
• category III (moderate infectivity):
• bone marrow
• liver
• lung
• mucous membrane of the nose
• pancreas
• peripheral nerves could carry infectious prions from the brain to
• tongue : anyway mice injected with nerve cells from infected cow tongue remain healthy
• there are a number of papers out regarding the issue of prions being found in muscle. Indeed, since prions are believed to be associated with neural tissue, then it stands to reason prions can travel along any nerve path. One needs to understand the fundamentals of US Slaughter facilities to comprehend the situation. Cattle are humanely stunned with a captive bolt stunner that penetrates or piths the brain rendering the animal unable to feel pain. However, the animal is not dead. Depending upon the speed of the slaughter plant the animal remains alive, but unable to comprehend or feel pain, for an average of 2 to 7 minutes before the throat is cut, exsanguinating the animal. During that 2 to 7 minutes the neurological tissue that captive bolt compressed into the brain and into the blood stream can circulate throughout the body, as long as the heart beats. The prion is smaller than a red blood cell. Therefore, it would appear that the prion agent can be in muscle tissue.
• thymus
• lower part of the colon (distal).
• category IV (no detectable infectivity):
• mammary glands
• milk
• testicles
• ovaries
• fetal tissue
• uterus
• heart
• kidney
• urine
• seminal vesicle
• thyroid gland
• blood
• serum
• coagulae
• skeleton muscles
• saliva
• salivary glands
• feces
• gall bladder
• connective tissue
• hair
• skin
• bones
• cartilage tissue
The said list is not similar to the SRM list that covers organs prohibited from entering the food and feed chain. The latter have been selected while considering their relative risk factor as food for man and animals, which is related to quantitative aspects of their BSE-prion contents.
2 ewes (Ovis aries) fed 5 mg of BSE-infected material had lambs that died of BSE after showing signs of infection in their tonsils 546 days after birth. Their mothers had shown no outward signs of the disease at lambing, one showing them 73 days after lambing, and the other 198 days after. But it is still not certain that the lambs were infected while in the uterus, or shortly before or after lambing. The disease may have spread through the birthing fluids or in some other way. The evidence so far suggests this is far more likely than the lambs catching the disease from other apparently unaffected sheep. It is already known that BSE-like diseases can be transmitted via blood in humans as well as animals, but there has been no evidence that it has been handed from dam to calf in cattle, or mother to baby in people. The sheep involved were of a genetic type that in lab tests previously appeared most susceptible to BSE. But it is unclear how many such sheep are in flocks on farms. There are 15 different genotypes, and unlike in BSE in cattle, genetic type seems important. Unfortunately at present there would be no way of identifying resistant sheep in time for them to go into food, while banning others. The fear about sheep has existed for years because, until the late 1980s, they were fed the same sort of feed as cattle. However if it was ever in sheep, there is no suggestion that it ever existed on a large scale. There is some good news. The lambs that seem to have inherited BSE showed a brain signature similar to BSE in cattle. Officials have been worried that some BSE in sheep, if it existed, might have been masked by a similar disease called scrapie, not known to be dangerous to humans^ref
It will be also interesting to note whether results of controlled infection trials in bovines within the UK-based BSE research project, "Experimental production of bovine tissue for the validation of BSE diagnostic tests (SE1736)", have been published or might become available
One assumption lies at the root of efforts to keep the meat we eat safe from mad cow disease: If an animal with BSE falls ill with another infection, its immune response can carry large numbers of prions to organs throughout its body. In 2003, small amounts of prions in the muscle tissue of people who had died from vCJD were detected, suggesting that animal meat might harbour trace amounts of these disease proteins too. When prions were administered to mice with 5 inflammatory diseases of kidney, pancreas or liver, in all cases, chronic lymphocytic inflammation enabled prion accumulation in otherwise prion-free organs. Inflammatory foci consistently correlated with lymphotoxin upregulation and ectopic induction of PrP^C-expressing FDC-M1⁺ cells, whereas inflamed organs of mice lacking lymphotoxin- or its receptor did not accumulate PrP^Sc nor infectivity upon prion inoculation. The amount of prions in these organs was just as high as is generally found in diseased spleens : cells involved in the inflammatory response somehow help the prions to replicate, and to spread to the parts of the body being targeted by the immune reaction. By expanding the tissue distribution of prions, chronic inflammatory conditions may act as modifiers of natural and iatrogenic prion transmission^ref.
The age at which specified risk materials (SRM) (tissue such as brain and spinal cord) are removed from cattle slaughtered for food was set at 12 months in all European Union (EU) member states (except for the United Kingdom) in 2000. This measure was designed to protect consumers of beef from the risk of bovine spongiform encephalopathy (BSE)^{ref1, ref2}. New information supplied by the World Organization for Animal Health (OIE), surveillance data and scientific research was recently considered by members of the European Food Safety Authority Biological Hazards Panel. Based on this evidence and a review of previous discussions, the panel recognized that the bovine central nervous system is unlikely to become infectious until an infected animal is considerably older than 12 months^ref. The average age of cattle with BSE in the EU has increased between 2001 and 2004, from 86 months to 108, most likely due to effective control measures. It is further observed that the number of BSE cases reported at an age less than 35 months in past years in the EU has been only 4 out of a total number of 6520 BSE cases on a total of close to 41 million animals tested. The minimum age of BSE cases in the EU has been 28 and 29 months (2 animals) in 2001, 32 and 34 months in 2002, 36 months in 2003 and 42 months in 2004. The 3 youngest animals were emergency slaughter, whereas the remainder of BSE cases in young animals (i.e. younger then 48 months, table 1) included all target groups. Only 4 cases in cattle under 35 months have been reported since 2001. The lowest age of animals with BSE rose from 28 to 42 months between 2001-4. From pathogenesis studies of infectivity distribution throughout the incubation period, and the earliest age of clinical manifestation, it was concluded that a bovine central nervous system would not become infectious until at least 26 months of age, as it appears that only during the last quarter of the incubation period does the disease become detectable. The panel concluded that setting the age for SRM removal at 21 months would allow a reasonable safety margin. Based on this opinion, the European Commission will consider whether changes to the existing legislation should be proposed. There is currently no scientific basis for raising the age limit for bovine tonsil and intestine. The most significant factor which deserves to be taken into account when considering the age limit for the human consumption of SRM is the pace and rate of the feed ban implementation; in other words -- the time span elapsed since the actual, final withdrawal of ruminant Meat and bone meal (MBM) from cattle feed, and indeed -- in view of potential cross contamination -- also from the feed of other food animals. It seems that effective, full implementation had not taken place in the EU, as a whole, prior to the end of 2002. As stated in the report, breaches have been encountered even later. This delay deserves to be seen as a significant factor in the preference of EFSA'a Scientific Panel on Biological Hazards to choose and recommend a SRM age limit of 21 rather than 30 months. Other "GBR III" countries, such as Canada, have opted to apply a 30-months-age SRM limiti^ref. The EU has completed, since 2000, the assessment of the geographical BSE-risk (GBR) of 66 countries. 3 assessments have been carried out during 2005, relating to Costa Rica, El Salvador and Nicaragua, all 3 obtaining the status of GBR II ("Presence of one or more cattle clinically or pre-clinically infected with the BSE agent is unlikely but not excluded"). 7 other GBR assessments have been issued by EFSA in September 2004, relating to Canada, USA, Mexico, South Africa, Australia, Sweden and Norway^ref
• deers with CWD : efforts to find the infectious prion in the muscle of infected animals by seeing whether antibodies to the prion could find any and bind to them have previously failed. But Telling's lab has now shown, using transgenic mice, that disease prions can reside in the muscle of deer infected with CWD. The team replaced the gene for the normal mouse version of the prion protein with the normal gene from deer, so the mice made the normal, healthy deer protein. They then injected the mouse brains with tissue from infected deer. 12 to 18 months later, the mice developed encephalopathy. Tissues from both the infected deer's brains and thigh muscles caused disease. Muscle took slightly longer to cause disease than brain tissue, showing it had slightly less prion. We don't know that it is transmitted in the wild by animals eating muscle from infected animals. We now have to see where else the prion might be, including saliva and even excrement, using more transgenic mice. Because we tested deer that were already ill, we don't know what the distribution of prion is in animals that are still incubating the disease. Hunters have been warned by wildlife agencies not to kill and eat obviously ill animals, but an animal not yet showing signs of the disease might still carry the abnormal prion, albeit less of it. It is also unknown whether people can catch encephalopathy by eating  CWD-infected meat, as they can from eating BSE-tainted meat^ref
• studies to test the transmissibility of the BSE agent to pigs (Sus scrofa) began in 1989. Parenteral inoculation of the agent by three routes simultaneously (intracranially, intravenously and intraperitoneally) produced disease with an incubation period range of 69-150 weeks. Pre-clinical pathological changes were detected in 2 pigs killed electively at 105 and 106 weeks post-inoculation. Infectivity was detected by bioassay in inbred mice in the CNS of those pigs that developed spongiform encephalopathy. Infectivity was also found in the stomach, jejunum, distal ileum and pancreas of terminally affected pigs. These findings show that pigs are susceptible to BSE. In contrast, disease failed to occur in pigs retained for 7 years after exposure by feeding BSE-affected brain on three separate days, at 1-2 week intervals. The amounts fed each day were equivalent to the maximum daily intake of meat and bone meal in rations for pigs aged 8 weeks. No infectivity was found in tissues assayed from the pigs exposed orally. This included tissues of the alimentary tract. It is suggested that these pigs did not become infected. The relatively high oral exposure used in these experiments compared with feed-borne exposure in the field may explain the absence of an epidemic of spongiform encephalopathy in domestic pigs concurrent with the BSE epidemic in the UK^ref. Pigs and poultry in the United Kingdom have undeniably been exposed to the BSE agent. They consumed the same ruminant protein that gave rise to the BSE epidemic in cattle, but there has been no evidence of an epidemic in these species. Experimental investigations have shown pigs to be susceptible to infection by multiple parenteral challenge, but resistant to oral exposure with BSE-infected cattle brain. Current but incomplete evidence suggests that they are also resistant to oral challenge with sheep scrapie. Studies in domestic chickens indicate that they are resistant to both parenteral and oral challenge. Unfortunately, no published data exists on the susceptibility of fish to infection. Incidental findings in the brains of unexposed pigs are described that could otherwise give rise to concerns aboutthe presence of a transmissible spongiform encephalopathy in pig populations around the world^ref. In an experimental study of the transmissibility of BSE to the pig, seven of 10 pigs, infected at 1-2 weeks of age by multiple-route parenteral inoculation with a homogenate of bovine brain from natural BSE cases developed lesions typical of spongiform encephalopathy. The lesions consisted principally of severe neuropil vacuolation affecting most areas of the brain, but mainly the forebrain. In addition, some vacuolar change was identified in the rostral colliculi and hypothalamic areas of normal control pigs. PrP accumulations were detected immunocytochemically in the brains of BSE-infected animals. PrP accumulation was sparse in many areas and its density was not obviously related to the degree of vacuolation. The patterns of PrP immunolabelling in control pigs differed strikingly from those in the infected animals^ref. A new study details transplanting swine organs to people and the possibility of TSE disease being transmitted. Research Project: Transmission, Differentiation, and Pathobiology of Transmissible Spongiform Encephalopathies, National Animal Disease Center Virus and Prion Diseases of Livestock, Evaluation of a diet free of animal protein in germfree swine. 2 experiments were conducted in which germfree pigs or pigs monoassociated with Lactobacillus paracasei subspecies paracasei were fed either a traditional milk-based diet (Esbilac) or an experimental diet free of animal protein (DFAP). Throughout the 16-day study, animals' clinical condition, total weight gain, feed conversion, and bacterial contamination were monitored. At the conclusion of the study the animals were killed, necropsied and tissues sampled for L. paracasei isolation. General pig disposition remained consistent between treatment groups and trials, except for two animals that developed mild diarrhoea during trial 1. All pigs remained viable during the study irrespective the diet fed or probiotic inoculation. Germfree pigs fed the Esbilac diet gained on average a total of 1034 +/- 63.0 g, and had a feed conversion ratio of 0.17 +/- 0.01 g of gain per 1 ml of diet. Germfree pigs fed the experimental diet gained on average a total of 599 +/- 151 g, and had a feed conversion ratio of 0.10 +/- 0.02 g of gain per 1 ml of diet. Monoassociated pigs fed the Esbilac diet gained on average a total of 862 +/- 70.3 g, and had a feed conversion ratio 0.14 +/- 0.01 g of gain per 1 ml of diet. Monoassociated pigs fed the experimental diet gained on average a total of 563 +/- 96.8 g, and had a feed conversion ratio of 0.09 +/- 0.02 g of gain per 1 ml of diet. Lactobacillus paracasei established extensively in pigs fed either the Esbilac or experimental diets. Lactobacillus paracasei had no effect (P >0.05) on piglet growth and did not display any interactions based on the diet fed. Measured growth parameters were statistically different (P <0.05) based on the diet fed and variance seen between trials. In conclusion, a DFAP has been developed and has been shown to be capable of sustaining life in piglets up to 16 days of age^ref.
• risk from injection of chicken breast or tumbling of chicken meat with water and other beef proteins to enhance the weight to increase profit margins has still to be assessed
In humans, even if current opinion holds that prions infect people through the stomach, prions might enter via small wounds on the tongue : the incubation period following TME agent inoculation into the lingual muscles was the shortest (around 80 days) among the 5 nonneuronal routes of inoculation, including another intramuscular route and oral route (190 days). Deposition of the abnormal isoform of the prion protein, PrP^Sc, was first detected in the tongue and submandibular lymph node at 1 to 2 weeks following inoculation of the tongue with TME. PrP^Sc deposits in the tongue were associated with individual axons, and the initial appearance of TME in the brain stem was found in the hypoglossal nucleus at 2 weeks postinfection. At later time points, PrP^Sc was localized to brain cell groups that directly project to the hypoglossal nucleus, indicating the transneuronal spread of TME. TME PrP^Sc entry into the brain stem preceded PrP^Sc detection in the rostral cervical spinal cord. These results demonstrate that TME can replicate in both the tongue and regional lymph nodes but indicate that the faster route of brain invasion is via retrograde axonal transport within the hypoglossal nerve to the hypoglossal nucleus. Topical application of TME to a superficial wound on the surface of the tongue resulted in a higher incidence of disease and a shorter incubation period than with oral TME ingestion. Therefore, abrasions of the tongue in livestock and humans may predispose a host to oral prion infection of the tongue-associated cranial nerves^ref. HY strain of the TME PrP^Sc accumulates within skeletal muscle cells, in addition to axons, in the tongue of hamsters following intralingual and intracerebral inoculation. Localization of PrP^Sc to the neuromuscular junction suggests that this synapse is a site for prion agent spread between motor axon terminals and muscle cells. Following intracerebral inoculation, the majority of PrP^Sc in the tongue was found in the lamina propria, where it was associated with sensory nerve fibers in the core of the lingual papillae. PrP^Sc staining was also identified in the stratified squamous epithelium of the lingual mucosa. These findings indicate that prion infection of skeletal muscle cells and the epithelial layer in the tongue can be established following the spread of the prion agent from nerve terminals and/or axons that innervate the tongue. Ingestion of meat products containing prion-infected tongue could result in human exposure to the prion agent, while sloughing of prion-infected epithelial cells at the mucosal surface of the tongue could be a mechanism for prion agent shedding and subsequent prion transmission in animals^ref. These findings suggest that food products containing ruminant or cervid tongue may be a potential source of prion infection for humans. Sensitive western blotting revealed consistent PrPSc accumulation in skeletal muscles from forelimb and hindlimb, head, back and shoulder, and in tongue of hamsters orally infected with scrapie^ref. When the process of eating and digesting infected meat is mimicked by mashing up brain tissue that contained prions from patients who had a form of CJD and exposing it to a range of harsh proteases from the mouth, stomach and intestine, prions escape this attack almost unscathed, as does ferritin, which is abundant in meat. The 2 proteins seem to stick together. By attaching fluorescent tags to the 2 proteins, they showed that they are transported through a growing sheet of human Caco-2 intestinal epithelial cells hand-in-hand^ref. Prions can also pass through the gut unaided, through M cells^ref. The ferritin protein is almost identical in a wide range of species, which might allow it to latch on to and ferry foreign prions from cows : ferritin might transport prions to humans from other animals with prion disease, such as deer and elk suffering from chronic wasting disease. Hobbling the transport of ferritin might block prions from entering the body, but this would be difficult to use therapeutically because people would have to be treated at the time when they were being exposed, which is many years before symptoms of the disease emerge.
Of 2 macaques given a 5 g oral dose of brain homogenate from a BSE-infected cow, 1 macaque developed vCJD-like neurological disease 60 months after exposure, whereas the other remained free of disease at 76 months^ref.
• corneal allograft from infected donor
• maternal transmission : the Chief Medical Officer for England asked SEAC to consider current evidence and comment on the potential transmission of variant Creutzfeldt-Jakob disease (vCJD) from mother to child via human breast milk. In utero transmission was also considered. The committee also commented on the scientific basis of a risk reduction measure for possible transmission of vCJD via banked breast milk. No diagnostic test is currently available for the detection of abnormal PrP in milk. Research is under way to develop tests to screen for the possible presence of abnormal prion protein (PrP) in milk samples from cattle experimentally infected with BSE [A joint FSA/SEAC milk working group is monitoring and providing advice on this research carried out at the Veterinary Laboratories Agency.] These modified tests may also be applicable to human milk. However, it is not yet clear when/if a reliable test will be available. A small number of breast milk banks in the UK supply highly vulnerable premature babies for whom no milk may be available from the mother. A model developed by the Department of Health to assess the effect of pooling breast milk from multiple donors on the possible risks of transmission of vCJD via breast milk banks was considered. There is some, albeit limited, published epidemiological and experimental research on maternal transmission of prion diseases. There are also unpublished surveillance data of children born to vCJD cases from the National CJD Surveillance Unit and UK surveillance of neurological illness in children which might inform on potential risks of maternal transmission. There is no evidence that vCJD infectivity has ever been transmitted through breast milk. However, a theoretical risk exists. Modelling studies clearly show that the practice of pooling breast milk increases the number of donors to which a recipient is exposed and thereby increases the potential risk of an infant receiving milk contaminated with vCJD infectivity. The theoretical risk of infection can be minimised by not pooling the milk, by the use of individual hand operated breast milk pumps for single donors, and by the use of single-use sterilised bottles for collection. In addition, available evidence suggests that infection/inflammation of the breast results in increased lymphocytes in milk and therefore increased risk of infectivity. This risk would be minimised if milk from donors showing signs of infection were not used. The committee suggested that, if practicable, milk could be stored for an appropriate period of time to allow the health status of donors to be monitored, before it is released. However, information was not available to the committee on whether long-term storage of human milk is detrimental to its nutritional quality. There is evidence from animal studies for low-level maternal transmission of prions in cattle and sheep. This transmission may occur in utero, via milk and/or perinatally. However, the possibility that this putative maternal transmission might have been due to another mode of transmission, for example through a contaminated environment or feed, cannot be ruled out. In contrast, in humans there is no evidence for maternal transmission in cases of familial prion disease, other than the transfer of a mutant form of the PrP gene, and there is no evidence of maternal transmission of kuru. However, compared with other human prion diseases vCJD may pose a greater risk because of the greater involvement of the lymphoreticular system in vCJD pathogenesis. Although, breast tissue (and placenta) from a single vCJD case tested negative for PrPvCJD, transfer of infectivity to breast milk may depend on the physiological status of the mammary gland. Similar tests or infectivity bioassays have not been conducted on breast tissue from lactating patients with vCJD. A published study suggesting transmission of sCJD in colostrum^ref was considered unreliable because tissues not normally associated with high levels of infectivity (blood and placenta) showed equivalent infectivity to that of the brain in this study. Analysis of prospective surveillance data of UK children born to mothers with, or that had subsequently developed clinical vCJD, provide no evidence for maternal transmission of vCJD. However, the number of cases is very small and the incubation period of vCJD, if transmitted from mother to child, is unknown and so the children may yet be too young to have developed symptoms. The phenotype of BSE infection in humans expressing PrP genotypes other than M/M at codon 129 is not known. Given recently published studies in mice expressing the human PrP gene^ref, which suggest that the human PrP genotype may affect disease phenotype, the committee considered it very important that undiagnosed neurological diseases be carefully monitored. In this respect, amongst others, it is recommended that the careful monitoring of neurological illnesses through the PIND surveillance of children^ref continue. In summary, there is currently no pidemiological evidence for maternal transmission of vCJD, including transmission via breast milk. However, there is a hypothetical risk. Although available evidence is limited and mostly indirect rather than direct, this risk, if any, appears to be low. As a risk cannot be excluded, a watching brief should be maintained.
• cosmetics tainted with BSE : the FDA is urging cosmetic firms to not use certain cattle-derived substances in their products, because consumers run a slight risk if they apply  to open cuts
• plasma components : epidemiologic evidence of the absence in humans of disease transmission can probably be explained by the absence of significant plasma infectivity until the onset of symptomatic disease, and comparatively low levels of infectivity during the symptomatic stage of disease; the reduction of infectivity during plasma processing; and the need for at least 5-7 times more infectious agent to transmit disease by the intravenous than intracerebral route. These and other factors probably also account for the absence of transmission after the administration of whole blood or blood components. Anyway 2 cases have been reported in UK :
• 1st case : a 62-yrs old man who received 5 non-leucodepleted unit of red cells during an operation in 1996. One of these units was traced to a 24-year-old donor in whom vCJD developed >3 years after the blood was donated, dying shortly afterwards. In 2002 (6.5 years after the transfusion), vCJD developed in the recipient, who died 13 months after illness onset. An autopsy confirmed the diagnosis of vCJD. 1 other person is thought to have received blood from the same donor. The pulvinar sign was not seen on brain MRI and tonsil biopsy was not done. The cause of death was recorded as dementia. After autopsy, neuropathology was thought to be suggestive of CJD, and vCJD was subsequently confirmed by neuropathological examination; the clinical presentation of vCJD in the case was judged typical of vCJD^ref.
• 2nd case : a ?-years old man received a single non-leucodepleted unit of erythrocytes in 1999 from a donor who developed vCJD 18 months after blood was donated. The recipient died of a ruptured aortic aneurysm 5 years after the transfusion. Tests of the patient's spleen and cervical lymph node detected protease-resistant prion protein with a Western blot mobility pattern and glycoform ratio similar to those seen in other vCJD patients. These results and the absence of neurologic symptoms and brain pathologic findings indicated that this patient had a subclinical vCJD infection. Prion protein gene sequencing showed heterozygosity for methionine and valine at codon 129, which indicated that persons not homozygous for methionine (>50% of the population) can be infected by the vCJD agent^ref. Whether non-homozygotes can also develop vCJD, albeit with a longer incubation period, is as yet unknown : this suggests that wider groups of people could be at risk than was thought. According to a Finnish study, 42% (37% ?) of the UK population is MM homozygous at PRNP codon 129, with 47% heterozygous methionine/valine (MV) and the remaining 11% homozygous for valine (VV)^ref. vCJD was successfully transmitted to mice with all 3 human genotypes, but behaved differently in each. Transmission occurred least easily in the 16 VV mice compared to the 16 with the MV gene pattern and the 17 with MM. However, most of the MV animals did not develop clinical signs of vCJD during their short lifetime compared to those with MM, most of whom did. Only one mouse with VV showed signs it had contracted the disease, though it had no clinical symptoms. The absence of detectable brain PrPSc in the MV patient precluded molecular strain typing of prions. Although Peden and colleagues showed that splenic PrPSc from this case resembled that seen in vCJD^ref,6 this demonstration required use of phosphotungstic acid precipitation of PrPSc, which interferes with molecular strain typing^ref.3 Additionally, type 5 PrPSc, seen in vCJD-inoculated transgenic mice expressing human PrP 129V, but not yet documented in humans, has a similar glycoform profile^{ref1, ref2, ref3}.12, 20 and 23 This patient might have been propagating a prion strain distinct from that causing vCJD. Importantly, Peden and colleagues noted that they were unable to detect PrPSc in lymphoid follicles in tonsil, appendix, or large intestine from their patient, although abnormal PrP was detected in spleen and in a cervical lymph node. Although concentrations of PrPSc seen in their case were low^ref,6 perhaps indicating an early stage of incubation, PrPSc levels are generally higher in tonsil than elsewhere in the lymphoreticular system in vCJD^{ref1, ref2}.2 and 3 Because tonsillar involvement has to date been invariably seen in clinically affected cases of vCJD, Peden and colleagues speculated that this case might represent a distinctive pathogenesis related to route of exposure (intravenous rather than the oral route of exposure to BSE prions presumed in primary vCJD), and that the absence of a species barrier in secondary (person-to-person) infection might also affect phenotype. The current findings argue against these interpretations, and suggest that absence of tonsillar PrPSc in the MV blood recipient might have been due to the effect of PRNP genotype and perhaps selection of a distinctive prion strain. The patient's clinical course was characterised by a prolonged prodromal illness with fluctuating fatigue and clouded thinking, preceding progressive neurological deficit by 2 years. This case illustrates a clinical course of human vCJD prion infection characterised by five stages. A preclinical incubation phase of about 6 years occurred after blood transfusion, followed by a prodromal phase with fluctuating exertional fatigue and impaired concentration lasting about 18 months, and during which routine clinical examination and MR neuroimaging remained normal. Progressive neurological decline then consisted of an approximately 9-month initial phase of progressive ataxia, impaired manual dexterity, and dysaesthetic limb pain with substantial cognitive impairment but retained communication and comprehension of routine daily activities. A late neurological phase with severe cognitive decline and impaired verbal communication of about 4 months was followed by a shorter terminal phase in which the patient was bed-bound, mute, and only partly responsive. Route of infection with prions is known to affect clinical phenotype^ref7 and, if directly related to prion infection, the lengthy fluctuating prodrome in this case might be a consequence of infection through blood transfusion. The early symptoms of vCJD are usually reported as non-specific, and detailed neurological examination in this patient at an unusually early stage in the clinical disease course was normal. The subsequent neurological decline characterised by progressive ataxia, cognitive impairment, and painful limb symptoms, was typical of vCJD. vCJD has an insidious clinical onset, and its early features—such as depression, anxiety, personality change, and sensory disturbances—are highly non-specific. Early diagnosis is therefore difficult in the absence of another reason to suspect prion infection. This case illustrates the importance of diagnosis as early as possible in the clinical course. The patient was able to consider the option of joining a therapeutic clinical trial, to fully discuss the implications of his diagnosis, and to communicate his wishes to the clinical team and his family, making decisions and arrangements about his future care and other affairs. Specialist monitoring and investigation of high-risk groups, such as recipients of blood transfusion from a donor who developed vCJD, should allow the condition to be recognised at an early stage. Careful clinical assessment remains the most important element in the early detection of symptomatic disease. The most useful non-invasive investigation in advanced cases of vCJD has been MR neuroimaging, particularly the FLAIR sequence^ref.24 Early case reports noted bilateral increased signal in the posterior thalamus (pulvinar) on T2 weighted images^ref.25 A retrospective review of MR scans from 36 histologically confirmed cases of vCJD, with a control group composed mainly of patients with other forms of human prion disease, suggested that the pulvinar sign occurred frequently in advanced cases of vCJD^ref.26 These investigators reported a sensitivity of up to 86% and specificity of up to 96% in this series, but suggested that this sign might be a late feature of the disease process. Histologically confirmed cases of vCJD with minimal or absent pulvinar changes on MR neuroimaging at a mean 10.5 months during an illness of mean 15 months duration were identified in this series. Values of 81% sensitivity and 94% specificity have also been reported in a series including 27 cases of vCJD diagnosed by tonsil biopsy^ref.27 As these studies suggest, the pulvinar sign is not specific for vCJD. These MRI appearances are described in sporadic CJD28 and paraneoplastic limbic encephalitis^ref,29 both of which are important considerations in the differential diagnosis of patients with suspected vCJD. Pulvinar signal change on MRI is also reported in several rare conditions that might otherwise be distinguished from vCJD on clinical grounds, such as benign intracranial hypertension^ref,30 status epilepticus associated with cat scratch disease^ref,31 Alpers' disease^ref,32 and post infectious encephalitis^ref.33 As this present case further exemplifies, the absence of characteristic MR findings does not exclude a diagnosis of vCJD. In fact, this case provides important insights into the relation of the pulvinar sign to clinical progression of the disease, suggesting that it could be a late feature. Quantitative MR spectroscopy studies in a small series of patients raises the possibility that more sensitive techniques might be helpful earlier in the clinical course^ref.34 Tonsillar biopsy remains the most sensitive and specific diagnostic procedure for vCJD^{ref1, ref2, ref3, ref4, ref5}.2, 3, 14, 25 and 33 Tonsillar PrPSc is uniformly present in clinically affected cases of vCJD but not in other forms of human prion disease, including iatrogenic CJD associated with use of human cadaveric derived pituitary hormones, arguing that this distinctive pathogenesis relates to effect of prion strain rather than to a peripheral route of infection^{ref1, ref2, ref3}.2, 3 and 35 As infection of lymphoreticular tissues is thought to precede neuroinvasion, and indeed has been detected in archived surgical samples removed before development of vCJD^{ref1, ref2},36 and 37 it is likely to allow firm diagnosis at the early clinical stage or indeed pre-clinically^ref.7 The case described here confirms that tonsillar infection occurs in secondary vCJD prion infection, at least in PRNP 129MM individuals. This finding is also of relevance to interpretation of results in due course from analysis of the National Anonymous Tonsil Archive, which aims to screen 100 000 tonsils for disease-associated PrP to estimate prevalence of vCJD prion infection in the UK population^ref.38 Given the advent of experimental therapeutics for prion disease, including the MRC PRION-1 trial^{ref1, ref2}7 and 10 tissue diagnosis might be considered for asymptomatic individuals from high-risk groups so that early access to therapeutic trials can be offered, ideally before neuroinvasion, at a stage when infection may be more accessible or responsive to therapeutic intervention. Until further data are obtained on lymphoreticular pathogenesis in patients with the PRNP 129 VV and MV genotypes it would be prudent to consider biopsy of lymph nodes as well as tonsil in such patients. Since the successful interruption of disease progression in peripherally infected laboratory mice with monoclonal antibodies against prion protein, the future use of humanised versions of these antibodies in secondary prophylaxis might also be possible in individuals known to be at high risk of developing clinical forms of human prion disease^ref.39 All individuals found to have received potentially infected blood are now notified of their risk status, inevitably causing distress and uncertainty. Counselling in this situation, including discussion of public-health risks and management options, has parallels with counselling for people at risk of inherited forms of prion disease. Individuals will differ in their wishes for further investigation and early diagnosis, but all should be given the opportunity of immediate access to specialist advice, assessment, and long-term support^ref.
• 3rd case : a 31-year-old male patient presented to the National Prion Clinic in 2005, with a 6-month history of progressive balance difficulties and impaired concentration. He had incapacitating leg pains and increasing difficulty walking. The patient had suffered from ulcerative colitis since his teenage years. A severe relapse of symptoms at age 22 years had led to surgical intervention with a colectomy and ileostomy. In 1997 (age 23 years), the ileostomy had been converted to an ileoanal J-pouch. Complications in the immediate postoperative period included pelvic bleeding: the patient was transfused with 22 units of red cells, 15 units of fresh frozen plasma, and three platelet doses, and required a further laparotomy and intensive care management. He then made a good recovery. One of the donors of the non-leucodepleted red cells received by the patient developed vCJD 20 months after donating this blood. This donor was homozygous (MM) at PRNP codon 129 and died after an 11-month illness, with neuropathological confirmation of vCJD. The recipient was also homozygous (MM) at PRNP codon 129. 6 years after the vCJD-implicated transfusion (age 29 years), the patient had presented to his family doctor with a short history of fluctuating exertional fatigue and impaired concentration. This problem was presumed to have followed a viral upper respiratory tract infection. Symptoms fluctuated, and around this time the patient and his doctor were notified of his exposure to a vCJD-implicated transfusion in 1997, and that he was considered to be at risk of vCJD. Neurological examination, including clinical cognitive assessment, was normal and no biological symptoms of depressive illness were noted. Routine electroencepahlogram and MR neuroimaging were normal (figure 1A and 1B). Some symptomatic improvement occurred, sufficient for the patient to return to work. At neurological review after a further year, persistent symptoms of fatigue and impaired concentration were noted with no abnormal examination findings. 6 months later (age 31 years), 7·5 years after the vCJD-implicated transfusion, progressive neurological symptoms led to referral to the National Prion Clinic. The patient reported a sense of imbalance on turning with a tendency to stagger. Memory problems were becoming more prominent and he reported difficulties in recalling details of events in the preceding few days. He described a sense of tremor in his hands with reduced manual dexterity. Within a few weeks he reported severely incapacitating leg pains as an unvarying “searing pain” worsened by activity and eased by rest. Although most prominent in the anterior thighs, this pain affected the whole of both legs with hypersensitivity and paraesthesiae on touching the feet but no numbness or sensory loss. Examination 6 months after the onset of progressive neurological symptoms showed an mini mental state examination (MMSE) score of 30/30, digit recall of 6 forward and 5 backwards, with no evidence of dyspraxia or visuospatial dysfunction. The patient could walk unaided but preferred to use a stick to ease his leg pains. Other than minimal first-degree gaze-evoked nystagmus, cranial nerve and other neurological examination was normal. Neurological decline continued with more prominent cognitive impairment. 6 weeks later, the patient's MMSE scored 22/30 (with errors in orientation for time, delayed recall, and serial subtraction). He was increasingly unsteady. Caregivers reported several falls, and the patient indicated that limb pains were less severe. Results of routine haematological and biochemical investigations, infection screen, and nerve conduction studies were normal. At this stage, MR neuroimaging showed symmetrical abnormal increased T2 and fluid attentuation inversion recovery (FLAIR) high signal within the posteromedial thalamus, consistent with the pulvinar sign (figure 1, C and D). Non-specific changes were evident on electroencepahlogram. PRNP genotyping excluded genetic mutations associated with inherited prion disease and showed codon 129 methionine homozygosity. Tonsil biopsy was declined. The patient elected to join the quinacrine arm of the MRC PRION-1 trial10 and began treatment with quinacrine at 300 mg daily. Subsequently the patient continued to decline with progressive cognitive impairment, ataxia, and dysarthria. He became bed-bound and poorly responsive before admission for hospice care. In line with the expressed wishes of the patient and his family, medical intervention was kept to a minimum and neither gastrostomy nor nasogastric feeding were instituted. The patient died 8 years and 8 months after the vCJD implicated transfusion (age 32 years) and an autopsy was done. Brain and tonsil tissue were collected at autopsy and assessed for the presence of disease-related PrP by immunoblotting and immunohistochemistry. Immunoblotting of frontal cortex showed the presence of type 4 PrPSc (figure 2A, figure 3) pathognomic of vCJD.11 Immunohistochemical analysis of brain showed widespread deposition of abnormal PrP in all cortical areas and throughout the cerebellum, with occurrence of abundant florid PrP plaques (figure 4A and 4B) characteristic of vCJD.13 Spongiform change, gliosis, and distribution of PrPSc were indistinguishable from those found in previous cases of vCJD. Immunoblot analysis of lymphoid tissue from tonsil showed the presence of type 4t PrPSc,2 at a concentration of about 1% of the level of PrPSc detected in brain (figure 2B). Immunohistochemical analysis of tonsil showed multiple lymphatic follicles containing an abnormal PrP immunostaining pattern typical of that seen in vCJD (figure 4c).14 Spleen was also positive. The patient had ulcerative colitis. Experimentally induced chronic inflammatory foci can act as sites for prion propagation.16 Although ulcerative colitis is a relatively common condition and not infrequently necessitates blood transfusion, it will be of interest to see if future cases had co-existent chronic inflammatory conditions at the time of prion exposure, which might indicate a role in susceptibility or incubation periods.
• 4th case : a patient who developed symptoms of vCJD 8.5 years after receiving a transfusion of red blood cells from a donor who developed vCJD about 17 months after this blood was donated^ref. The donor to this case also donated the vCJD-implicated blood transfused to the 3rd case. As for all other reported clinical vCJD cases that have been tested for genotype, this patient is a methionine homozygote at codon 129 of the prion protein gene. The patient is currently alive^ref.
• an elderly woman who received a blood transfusion in 1999 from a donor who later died from vCJD died from an unrelated medical condition : she harbored prions in her spleen and cervical lymph nodes
All 4 cases had received transfusions of non-leucodepleted red blood cells between 1996 and 1999. Since October 1999, leucocytes have been removed from all blood used for transfusion in the UK. The effect of leucodepletion on the reduction of the risk of transmission of vCJD from an infective donation is uncertain.
The pathogenesis of vCJD differed substantially from that of sporadic or classical CJD by showing prominent and uniform prion accumulation in lymphoreticular tissues^{ref1, ref2}2 and 3 akin to ovine scrapie, where prionaemia has since been demonstrated experimentally^ref.4 Transmission of prion diseases between species are generally associated with much longer mean incubation periods than within-species transmissions, because of the so-called species or transmission barrier effect.1 Therefore, mean incubation periods of secondary vCJD (involving person-to-person transmission) would be expected to have considerably shorter mean incubation periods than in primary vCJD resulting from exposure to BSE prions. That the incubation periods seen in the first cases of secondary vCJD, by definition those with the shortest incubation periods, were 6–6·5 years suggests that the shortest incubation periods of primary vCJD are longer, especially as the oral route of transmission is also typically associated with longer incubation periods than parenteral routes. A preliminary estimate of the shortest incubation periods of primary vCJD, based on the youngest cases seen, is around 12 years, which would be consistent with such extrapolation from the shortest incubation periods in secondary vCJD.15
The chances that 3 confirmed infections among people who received blood was caused instead by eating mad-cow tainted beef were remote -- 1 in 80,000 to 1 in 1 billion. There is a concern that individuals who are incubating the disease, who themselves don't show any evidence of the disease, could still pose a risk to others, if they were blood donors, or if they had an operation which involved instruments contacting infected tissues : in March 2004 Britain banned people who had had transfusions over the past 24 years from donating blood to reduce the risk of spreading the disease. The cohort of identified recipients of blood transfusion from donors who subsequently developed vCJD totals 66 individuals, of whom 42 have died (including the 3 deaths reported above) and 24 are alive. The donated plasma was used to manufacture factor VIII, factor IX, antithrombin, intravenous immunoglobulin G, albumin, intramuscular human normal immunoglobulin, and anti-D. In total, 6000 letters are to be sent out informing patients of the risk assessment -- although only 2/3 are being told they may be at direct risk^ref. The CJD Incidents Panel (CJDIP) advises certain special public health precautions need to be taken for recipients of UK sourced plasma products who have been exposed to a > 1% potential additional risk of vCJD infection, as these patients could pose a risk to others in defined circumstances. These at-risk patients are asked:
• not to donate blood, organs or tissues
• to inform their clinician if they need medical, surgical or dental treatment, so that infection control precautions can be taken to reduce any possible risk of spreading vCJD, and to consider informing their family, in case they (the patients) need emergency surgery in the future^ref
The CJDIP has categorised each batch of implicated plasma products according to the likelihood that special public health precautions need to be taken as follows:
• high: the amount of potential infectivity in product batches was high enough to warrant special public health precautions following the administration of a very small dose. These batches should be traced, and the recipients advised of their exposure and asked to take special public health precautions
• medium: substantial quantities of the material in question would need to have been administered to warrant special public health precautions. Efforts should be made to trace these batches and assess the additional risk to individual recipients to determine whether pecial precautions should be taken
• low: the potential additional risk to recipients is considered negligible. These batches do not need to be traced and the individual recipients do not need to be informed.
Britain has exported blood products that could be contaminated with the human form of mad cow disease to at least 11 countries, including India, in the late 1990s raising fears of further transmission of the deadly condition. Besides India, where 953 vials of albumin were sent, the other 10 recipient countries are Ireland (polio vaccine, 83 500 doses), Brazil (44 864 vials albumin, 80 vials immunoglobulin), Dubai (UAE) (2400 vials albumin), Turkey (840 vials immunoglobulin), Brunei (400 vials albumin), Egypt (144 vials albumin), Morocco (100 vials albumin), Oman (100 vials immunoglobulin), Russia (23 vials factor VIII) and Singapore (3 vials immunoglobulin).
Since 1998, plasma derivatives, such as clotting factors, have been prepared from plasma imported from the USA.
Since October 1999, leucoreduction has been implemented in the U.K. because of concerns about potential infectivity of vCJD in blood, or in blood components. In August 2002 fresh frozen plasma for treating babies and young children born after 1st January 1996 would be obtained from the USA. In December 2002, the Department of Health completed its purchase of the largest remaining independent US plasma collector, Life Resources Incorporated. This secures long-term supplies of non-UK blood plasma for the benefit of NHS patients.
They may also consider prion filtering, although this would be very expensive, and they could exclude donors of certain ages, although this would dramatically reduce blood supplies. One study presented to the committee suggested that Britain could be hit by a second wave of vCJD : there could be thousands of Britons infected with the deadly brain disease who do not show any symptoms. These carriers mean the infection could spread widely, through surgery or blood transfusions, even if tainted beef is removed from the food chain. There is a huge discrepancy between the number of people who have died and the number expected to die given the seeming prevalence of prions.
On March 2005 Japan reviewed its ban on blood donations from people who stayed in Britain or France -- 2 countries hit by mad-cow disease in the 1980s and 1990s -- for one day or longer between 1980 and 1996 after a deceased Japanese man was confirmed on February 2005 to have been infected with vCJD was likely to have contracted the human form of mad cow disease during a 24-day stay in Britain in 1990. The man also stayed in France for 3 days at around the same time that France w