[Prions, epidemic of Creutzfeldt-Jakob variant disease and global emergency]

We present here the current understanding of "prion" theory and global risk for epidemics of variant Creutzfeldt-Jakob disease (vCJD). Prion is the infectious agent of all transmissible spongiform encephalopaties (TSEs). It is regarded as an aggregate of a pathological conformer (PrPSc) of a normal cellular glycoprotein (PrPC) encoded by a gene, in humans on chromosome 20. The differences between PrPSc and PrPC are largely if not exclusively conformational; PrPC is mostly alpha-helical while PrPSc, beta-pleeted. Furthermore, mutations within the coding sequence (open reading frame) of PrP gene are linked with phenotypic expression of CJD, Gerstmann-Straussler-Scheinker disease (GSS) and fatal familial insomnia (FFI). VCJD is caused by transmission from cattle infected with bovine spongiform encephalopathy (BSE). PrP purified from vCJD-affected brains is characterised by the so called fourth type of glycosylation pattern. The neuropathological hallmark of vCJD is the florid plaque, an amyloid plaque surrounded by a corona of spongiform change. VCJD affects mostly young people (range: 13-74 years) and it is clinically distinguishable from sporadic CJD. The extent of epidemics is currently unknown; but its dynamic (102 cases until July 2001) may suggest "the worst" scenario.

[Transmissible spongiform encephalopathies. History, epidemiology, etiological, hyphotheses]

The history of transmissible spongiform encephalopathies is shortly reviewed beginning with the Westminster parliament act in the year 1755 up to the description in 1996 of the variant of the Creutzfeldt-Jakob disease, transmitted from cattle to man by alimentary route. The epidemiological patterns of encephalopathies of the various animal species and of the four encephalopathies up to date reported in man are shortly described: Creutzfeldt-Jakob disease, Kuru, Gerstmann-Straussler-Scheinker disease, Fatal Familial Insomnia. Etiological hypotheses are discussed until the identification of Prions: PrPcell, on the surface of normal cells, PrPscr in the brain of humans and animals dead for these diseases. The strains of the PrPscr are described on the basis of some characters observed through the passages in rodents and of molecular pattern. The possible future epidemiological evolution of the vCJD is also discussed.

Variant Creutzfeldt-Jakob disease

Variant Creutzfeldt-Jakob disease is caused by the transmission of bovine spongiform encephalopathy to humans. The clinical and investigative features of variant CJD are relatively distinct from sporadic CJD. The number of cases of vCJD are increasing with time in the UK, but the total future number of cases of vCJD is uncertain.

Distribution of the M129V polymorphism of the prion protein gene in a Turkish population suggests a high risk for Creutzfeldt-Jakob disease

A polymorphism (M129V) at codon 129 of the prion protein gene (PRNP) results in either a methionine residue (Met) or a valine residue (Val) and is known to determine susceptibility for the development of sporadic or acquired Creutzfeldt-Jakob disease (CJD). The distributions of M129V genotypes and alleles in various general populations have been reported and there are clear differences between Western Europeans and East Asians. We analysed the coding sequence of the PRNP gene in 100 healthy Turkish subjects to determine whether the distributions of the M129V genotypes and alleles or other PRNP gene variants in the Turkish population differ from those in other normal populations. Three known polymorphisms but no other gene variants were detected in the PRNP coding sequence of the Turkish individuals. Genotype frequencies at codon 129 were 57% Met/Met, 34% Met/Val and 9% Val/Val, with an allele frequency of 0.740:0.260 Met:Val. These distributions are considerably different from those reported for other normal populations residing in Western Europe and East Asia, except in Crete. The higher frequency of 129 Met-homozygotes in Turkey than in Western Europe suggests that the Turkish are at greater risk of developing CJD.

Control of infection in acupuncture

This paper is an update on infections, and potential infections, related to acupuncture, and a brief review of the relevant infection control procedures. There is no evidence at present to suggest that significant numbers of infections are being transmitted through standard acupuncture treatments in the UK. None the less, good infection control is essential. Like any other science, new research forces infection control to evolve and refine its procedures. Acupuncturists need to constantly review their standards as new viruses and risks are identified.

BSE did not cause variant CJD: an alternative cause related to post-industrial environmental contamination

The new prion diseases that have emerged in the last 15 years are bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (variant CJD). Although initially confined to the UK, these diseases have recently emerged in other European countries. The accepted cause of the human disease is that BSE spread from cattle to humans by the consumption of infected beef. However, the evidence that supports this is very thin. This article describes this evidence and lists a series of hypotheses concerning the cause of both BSE and variant CJD. The final hypothesis is based on recent evidence linking prion diseases to environmental factors including manganese. High environmental availability of manganese is associated with the prevalence of those prion diseases not linked to BSE. Therefore it is quite possible that BSE and variant CJD have emerged as a result of manganese-rich industrial pollution that has only occurred in the last century.

Variant Creutzfeldt-Jakob disease and blood transfusion

Variant Creutzfeldt-Jakob disease (vCJD) was first described in the United Kingdom in 1996 and is thought to have been transmitted from cattle infected with bovine spongiform encephalopathy probably via the food chain. Thus far just over 100 definite or probable clinical cases have been described, though the number of people currently infected and the eventual size and geographic distribution of any future clinical epidemic remain uncertain. There is little evidence that sporadic CJD is transmitted by blood transfusion. However, the same cannot necessarily be assumed to apply to the new variant strain of disease in which involvement of peripheral lymphoid tissues has been demonstrated. In the face of uncertainty surrounding the risk of transmission of vCJD by blood products, blood transfusion services in a number of countries have implemented precautionary policies, though whether in the long term these will prove to have been necessary or sufficient remains to be seen.

The first two patients with dura mater associated Creutzfeldt-Jakob disease in the Netherlands

Creutzfeldt-Jakob disease (CJD) can be transmitted through human growth hormone or gonadotrophin administration, dura mater or cornea transplantation, depth EEG monitoring and the use of contaminated neurosurgical instruments. We describe the first two dura mater associated CJD cases in the Netherlands. Ten and fourteen years before the onset of symptoms both patients received a Lyodura implantation. Findings are discussed in light of the growing epidemic of CJD among dura mater recipients.

Changing a single amino acid in the N-terminus of murine PrP alters TSE incubation time across three species barriers

The PrP gene of the host exerts a major influence over the outcome of transmissible spongiform encephalopathy (TSE) disease, but the mechanism by which this is achieved is not understood. We have introduced a specific mutation into the endogenous murine PrP gene using gene targeting to produce transgenic mice with a single amino acid alteration (proline to leucine) at amino acid position 101 in their PrP protein (P101L). The effect of this alteration on incubation time, targeting and PrP(Sc) formation has been studied in TSE-infected animals. Transgenic mice carrying the P101L mutation in PrP have remarkable differences in incubation time and targeting of central nervous system pathology compared with wild-type littermates, following inoculation with infectivity from human, hamster, sheep and murine sources. This single mutation can alter incubation time across three species barriers in a strain-dependent manner. These findings suggest a critical role for the structurally 'flexible' region of PrP in agent replication and targeting of TSE pathology.

[Mad cow disease and the new variant of Creutzfeldt-Jakob disease]

Bovine spongiform encephalopathy and the new variant of Creutzfeldt-Jakob disease (vCJD) belong to a family of similar diseases under the name of transmissible spongiform encephalopathies (TSE). It is demonstrated that the agent responsible for bovine spongiform encephalopathy (BSE) is also responsible for the new variant of Creutzfeldt-Jakob in man. This contribution describes the main characteristics of the two diseases.

Neuroinvasion by a Creutzfeldt-Jakob disease agent in the absence of B cells and follicular dendritic cells

With the potential spread of bovine spongiform encephalopathy to people as a variant Creutzfeldt-Jakob disease (CJD), it becomes critical to identify cells in the periphery that carry infection. Initial work with scrapie agents suggested that B cells were central vectors for neuroinvasion. Subsequent studies indicated that B cells played an indirect role by promoting the development of follicular dendritic cells (FDCs) that accumulate abnormal prion protein (PrP). The mechanism for the role of FDCs, however, has not been clear. To further dissect potential B cell functions that contribute to neuroinvasion, we inoculated a CJD agent into mutant mice that (i) lacked B cells, (ii) had B cells unable to secrete Ig, or (iii) could secrete only IgM. Remarkably, all these mice developed disease with practically indistinguishable incubation times. The demonstration that neither immune complexes nor B cells were required for neuroinvasion from the periphery mandates a reanalysis of the accepted view of the essential role of B cells and FDC in these infections. Moreover, immune complexes were not required for the accumulation of pathologic PrP on the surface of FDCs, suggesting that PrP can bind to FDCs autonomously or by means of another factor. Wild-type mice had incubation times approximately 50 days less than all mutant mice at the same peripheral doses, indicating that an intact immune system may increase agent uptake and delivery, but this condition is not essential. Specifically, the evidence to date suggests that IgG may enhance pivotal agent interactions with migratory myeloid cells.

Prion-induced neuronal damage--the mechanisms of neuronal destruction in the subacute spongiform encephalopathies

Prion diseases are characterized by the accumulation of a specific disease-associated isoform of the prion protein (PrP), termed PrPSc, which is the main, if not the only, component of the infectious agent termed prion. PrPSc is derived by an autocatalytic post-translational process involving conformational changes from the normal host-encoded isoform of the prion protein, termed PrPC. PrPC is a copper-binding glycoprotein attached to the cell membrane of neurons and other cells by means of a GPI anchor. The pattern of neurodegeneration differs between variants of prion disease and is related to the pattern of PrPSc deposition and differences in susceptibility of different cell types to the disease process. The pattern of PrPSc deposition depends on the strain of the agent and the PrP genotype of the host. Strain properties of prions appear to be related to different pathological conformations of PrPSc. Neuronal cell death is a salient feature in the pathology of prion diseases. Histological and electron microscopical studies have shown that cell death in prion disease occurs by apoptosis. Apoptosis of neuronal cells can also be induced in vitro by exposure to PrPSc or a neurotoxic peptide fragment corresponding to amino acids 106-126 of human prion protein (PrP106-126). Both in vitro and in vivo, the toxicity of PrPSc and PrP fragments appears to depend on neuronal expression of PrPC and on microglial activation. Activated microglial cells release pro-inflammatory cytokines and reactive oxygen species. Cell culture experiments suggest an important role of microglia-mediated oxidative stress in the induction of neuronal cell death. Only limited data are available on direct effects of PrPSc on neuronal cells. Potential effects include increased formation of an aberrant transmembrane form of PrP, termed CtmPrP, and changes in plasma membrane properties. In addition to direct and indirect toxic effects of PrPSc, a loss of function of PrPC may contribute to neuronal cell death. Potential mechanisms include disturbances in cerebral copper metabolism and antioxidative defense mechanisms. A better understanding of the pathogenesis of neuronal cell death in prion diseases may also have important therapeutic implications in the future.

Variant Creutzfeldt-Jakob disease: a summary of current scientific knowledge in relation to public health

The prion diseases pose unique scientific, medical, veterinary and regulatory challenges. Here, we summarize current information bearing on the natural history, pathobiology and epidemiology of these disorders and public policy responses to the potential threats to public health posed, particularly, by bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease (vCJD). Six years after the first case reports of vCJD, there is still no clear indication of the magnitude of the primary epidemic, or of the likelihood of lateral transmission of this untreatable disease by iatrogenic means, particularly by blood and blood products. However, the unsettling nature of the available evidence warrants prudence regarding public health policy and regulation, as well as a forward-looking approach to research.

Scrapie strains maintain biological phenotypes on propagation in a cell line in culture

Bovine spongiform encephalopathy (BSE) and its human equivalent, variant Creutzfeldt-Jakob disease (vCJD), are caused by the same strain of infectious agent, which is similar to, but distinct from, >20 strains of their sheep scrapie homologue. A better understanding of the molecular strain determinants could be obtained from cells in monoculture than from whole animal studies where different cell targeting is commonly a strain-related feature. Although a few cell types can be infected with different strains, the phenotypes of the emergent strains have not been studied. We have cured the scrapie-infected, clonal SMB cell line with pentosan sulfate, stably re-infected it with a different strain of scrapie and shown that biological properties and prion protein profiles characteristic of each original strain are propagated faithfully in this single non-neuronal cell type. These findings attest to the fact that scrapie strain determinants are stable and host-independent in isolated cells.

Creutzfeldt-Jakob disease: a protein disease

Creutzfeld-Jakob disease (CJD) is essentially a protein disease. All forms of CJD are characterized by the deposition of an abnormal coformation of a normal cellular protein. This protein (PrPc) is encoded for by the PRNP gene on chromosome 20 in humans. There are important genetic influences on susceptibility to CJD and on the resulting clinico-pathological picture. The abnormal protein (PrPSc), may be the infectious agent itself or the main component of it. However, its precise role in the pathogenesis of disease is not clear. The detection of PrPSc plays a crucial role in the diagnosis of CJD and its electrophoretic characteristics are used to classify different forms of CJD. However, the "molecular diagnosis" of CJD is not without uncertainties.

Creutzfeldt-Jakob disease: recommendations for disinfection and sterilization

Prion diseases constitute a unique infection control problem because prions exhibit unusual resistance to conventional chemical and physical decontamination methods. Recommendations to prevent cross-transmission of infection from medical devices contaminated by Creutzfeldt-Jakob disease (CJD) have been based primarily on prion inactivation studies. The recommendations in this article consider inactivation data but also use epidemiological studies of prion transmission, infectivity of human tissues, and efficacy of removing microbes by cleaning. On the basis of the scientific data, only critical (e.g., surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e., brain, spinal cord, and eye tissue) from high-risk patients--those with known or suspected infection with CJD--require special treatment.

The impact of glycobiology on medicine

Proteins essential to normal cell physiology are usually glycosylated and variation in their glycosylation patterns often leads to changes in their function. Changes in glycosylation pattern can also be associated with disease. It is now becoming increasingly clear how important it is to understand these changes, to gain insight into their involvement in disease mechanisms and the potential for novel therapeutic interventions.

Atypical form of dural graft associated Creutzfeldt-Jakob disease: report of a postmortem case with review of the literature

A postmortem case of an atypical form of dural graft associated Creutzfeldt-Jakob disease (CJD) is described. A 42 year old man developed progressive spastic paresis 163 months after a cadaveric dura mater graft. He presented with no myoclonus and very late occurrence of periodic synchronous discharges on EEG. The prion protein (PrP) gene was homozygous for methionine at the polymorphic codon 129. Neuropathological examination disclosed plaque-like PrP deposits with atypical distribution of synaptic PrP accumulations in the brain. This patient represents an atypical form of dural graft associated CJD characterised by unusual clinicopathological features.

Pathology of variant Creutzfeldt-Jakob disease

Variant Creutzfeldt-Jakob disease (vCJD) is a novel prion disease in man which was first described in 1996 in the UK. There is substantial evidence to indicate that vCJD represents the effects of the bovine spongiform encephalopathy (BSE) agent in man. The neuropathology of vCJD is characterised by the florid plaque, composed of a central amyloid core with a fibrillary periphery, surrounded by a rim of spongiform change in an intact neuropil. Unique patterns of PrP accumulation in vCJD are revealed by immunocytochemistry in the cerebral and cerebellar cortices, the basal ganglia, thalamus and brainstem. The neuropathology of the thalamus and midbrain is also characterised by severe neuronal loss and gliosis. vCJD is distinct from other human prion diseases in that disease-associated PrP accumulates within follicular dendritic cells in lymphoid tissue, and consistently in peripheral sensory ganglia. All vCJD patients so far have been methionine homozygotes at codon 129 in the PrP gene. There is no evidence to indicate that cases of BSE infection have occurred in individuals in the UK who are MV or VV at codon 129 in the PrP gene. It is conceivable that BSE incubation periods in these groups may be longer than in methionine homozygotes, hence the precise numbers of future cases of vCJD are difficult to estimate at present.