Iatrogenic Creutzfeldt-Jakob disease at the millennium

Prion disease: possible implications for oral health care

BACKGROUND

Prion diseases are a group of rare fatal neurodegenerative disorders in humans and animals that are histopathologically characterized by spongiform change within the central nervous system.

TYPES OF STUDIES REVIEWED

The author reviewed all available case reports and any studies of the oral aspects of prion diseases published in peer-reviewed journals and available via PubMed. He then outlined the risk of nosocomial transmission of prions in dental health care.

RESULTS

Sporadic Creutzfeldt-Jakob disease, or sCJD, is the most common of the acquired human prion disorders, and it typically affects elderly people and leads to rapid death. In contrast, variant CJD, or vCJD, has affected young adults from Europe, giving rise to a slow onset disorder comprising both psychiatric and neurological upset. Oral neurological manifestations are rare and seem to occur only in people with vCJD; there are no oral mucosal or gingival manifestations of prion disease. Prions can be detected in the oral tissues--usually the gingivae and dental pulp--of animals experimentally infected with prions. In contrast, prions have not been detected in the pulpal tissue of people with sCJD, and there are no data of pulpal infection in vCJD. There also are no data suggesting that prions are transmitted easily in the dental setting, but there remains the rare risk of such transmission if appropriate infection control measures are not adhered to.

CLINICAL IMPLICATIONS

Few people in the United States and worldwide have prion disease. Oral manifestations are rare. Evidence suggests that the risk of transmission and acquisition of a prion infection as a result of dental treatment is rare, if appropriate infection control measures are maintained.

Transmissible spongiform encephalopathies

Nosologically, transmissible spongiform encephalopathies (TSE or prion diseases) should be grouped with other neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, which are all caused by toxic gain of function of an aberrant form of a constitutively expressed protein. Failure to clear these proteins from the brain induces neuronal dysfunction. Transmissibility is the property that separates TSE from other neurodegenerative diseases, and this property seems to reside within the structure of the abnormal protein. The human phenotypic range of these encephalopathies includes Creutzfeldt-Jakob disease and its variant form, kuru, Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. Notwithstanding the generally low incidence of TSE and their limited infectiousness, major epidemics such as bovine spongiform encephalopathy and kuru arise in situations where intraspecies recycling of the abnormal protein is sustained. Moreover, evidence of chronic subclinical infection in animals offers insights into pathogenesis and prompts re-evaluation of the notion of species barriers and present infection control measures. Since case-to-case transmission is the only known mechanism underlying epidemics of TSE, potential reservoirs of infectivity in the tails of epidemics need continued vigilance.

Effects on instruments of the World Health Organization-recommended protocols for decontamination after possible exposure to transmissible spongiform encephalopathy-contaminated tissue

It has been recommended by the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) that rigorous decontamination protocols be used on surgical instruments that have been exposed to tissue possibly contaminated with Creutzfeldt-Jakob disease (CJD). This study was designed to examine the effects of these protocols on various types of surgical instruments. The most important conclusions are: (1) autoclaving in 1N NaOH will cause darkening of some instruments; (2) soaking in 1N NaOH at room temperature damages carbon steel but not stainless steel or titanium; (3) soaking in chlorine bleach will badly corrode gold-plated instruments and will damage some, but not all, stainless-steel instruments, especially welded and soldered joints. Damage became apparent after the first exposure and therefore long tests are not necessary to establish which instruments will be damaged.

The Epidemiology of Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) was identified as a new disease in 1996. It was linked to infection with the bovine spongiform encephalopathy (BSE) agent although the epidemiological evidence for this was not strong, but later strain typing studies confirmed the association. The disease has affected predominantly young adults whose dietary and other characteristics are unexceptional compared to control groups, other than that all patients to date have been methoinine homozygous at codon 129 of the prion protein gene and the incidence has been about two times higher in the North of the UK. The number of cases in the 7 years after first identification of the disease has been considerably lower than initially feared, given the likely widespread exposure of the UK population to the BSE agent through contaminated beef products. Predictions of the possible future course of the epidemic have many associated uncertainties, but current mathematical models suggest that more than a few thousand cases is unlikely. Such modelling is limited by the absence of a test for infection with the vCJD agent. The development of a test that could be used on easily accessible tissue to detect infection early in the incubation period would not only advance understanding of the epidemiology of infection with the agent but would also aid the implementation of control measures to prevent potential iatrogenic spread.

Prion (PrPres) allotypes profiling: a new perspectives from mass spectrometry

Biochemical methods employed for PrPres allotypes profiling are reviewed and compared with the latest mass spectrometric approaches. Emphasis is put on the advantages offered by a recently proposed electrospray strategy.

Neuropathology and molecular biology of variant Creutzfeldt-Jakob disease

The neuropathological features of human prion diseases are spongiform change, neuronal loss, astrocytic proliferation and the accumulation of PrP(Sc), the abnormal isoform of prion protein (PrP). The pattern of brain involvement is remarkably variable and is substantially influenced by the host PrP genotype and PrP(Sc) isotype. Variant Creutzfeldt-Jakob disease (vCJD) is a novel human prion disease which results from exposure to the bovine spongiform encephalopathy (BSE) agent. The neuropathology of vCJD shows consistent characteristics, with abundant florid and cluster plaques in the cerebrum and cerebellum, and widespread accumulation of PrP(res) on immunocytochemistry. These features are distinct from all other types of human prion disease. Spongiform change is most marked in the basal ganglia, while the thalamus exhibits severe neuronal loss and gliosis in the posterior nuclei. These areas of thalamic pathology correlate with the areas of high signal seen in the thalamus on magnetic resonance imaging (MRI) examination of the brain. Western blot analysis of PrP(Sc) in the brain in vCJD tissue shows a uniform isotype, with a glycoform ratio characterized by predominance of the diglycosylated band, distinct from sporadic CJD. PrP(Sc) accumulation in vCJD is readily detectable outside the brain, in contrast with other forms of human prion disease, particularly in the lymphoid system and in parts of the peripheral nervous system. This has raised concern about the possible iatrogenic transmission of vCJD by contaminated surgical instruments, or blood. All cases of vCJD are methionine homozygotes at codon 129 of the prion protein gene (PRNP). Continued surveillance is required to investigate cases of vCJD in the UK and other countries where BSE has been reported, particularly as cases of 'human BSE' in individuals who are MV or VV at codon 129 of the PrP gene have not yet been identified. Histological, genetic and biochemical techniques are essential tools for the adequate diagnosis and investigation of human prion diseases.

Subclinical prion infection

Prion diseases are transmissible neurodegenerative disorders that include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in humans. The principal component of the infectious agent responsible for these diseases appears to be an abnormal isoform of the host-encoded prion protein (PrP), designated PrP(Sc). Prion diseases are transmissible to the same or different mammalian species by inoculation with, or dietary exposure to, infected tissues. Although scrapie in sheep has been recognized for over 200 years, it is the recent epidemic of BSE that has centred much public and scientific attention on these neurodegenerative diseases. The occurrence of variant CJD in humans and the experimental confirmation that it is caused by the same prion strain as BSE has highlighted the need for intensive study into the pathogenesis of these diseases and new diagnostic and therapeutic approaches. The existence and implications of subclinical forms of prion disease are discussed.

Variant CJD: the present position and future possibilities

Variant Creutzfeldt-Jakob disease (CJD) is one of the transmissible spongiform encephalopathies (TSEs), or prion diseases, and is thought to be due to transmission of BSE from cattle to man via diet. These are characterized by the tissue deposition of an abnormal isoform of the normal cellular prion protein, a progressive, fatal neurological course and having the potential for infectivity. Infectivity is difficult to inactivate, and instances of iatrogenic CJD have been reported. The involvement of the tonsil, appendix and other lymphoid tissue in variant CJD has increased concerns about possible human-to-human spread.

Neuronal and astrocytic responses involving the serotonergic system in human spongiform encephalopathies

The relationships between the degree of cortical prion protein (PrP) deposition, tissue vacuolation and astrocytosis were studied in the frontal cortex of 27 cases of human spongiform encephalopathy, encompassing 13 cases of sporadic Creutzfeldt-Jakob disease (sCJD), four cases of familial CJD (fCJD) (one owing to E200K mutation, one owing to 144 bp insertion, one owing to P102L mutation and one owing to A117V mutation), five cases of iatrogenic CJD (iCJD) owing to growth hormone therapy and five cases of variant CJD (vCJD). The size and number of tryptophan hydroxylase (TPH) positive cells in the dorsal raphe were determined as an index of the function of the brain's serotonergic system. The amount of PrP deposited in frontal cortex in vCJD was significantly greater than that in both sCJD and iCJD, which did not differ significantly from each other. The extent of grey matter deposition of PrP correlated with that of white matter deposition. Deposition of PrP as plaques was greater in cases of sCJD bearing valine at codon 129 of PrP gene, especially when homozygous. However, all cases of vCJD displayed florid plaque formation yet these were homozygous for methionine at codon 129. Prion protein deposition as plaques was greater in cases of sCJD with 2A PrP isotype than those with 1 PrP isotype, similar to that seen in cases of vCJD all of which are 2B PrP isotype. There were no significant differences in the extent of astrocytosis between the different aetiological groups, in either grey or white matter, as visualized with glial fibrillary acidic protein (GFAP) or 5HT-2A receptor (5HT-2AR) immunostaining, although there was a strong correlation between the severity of 5HT-2AR and GFAP reactions within both grey and white matter. The extent of PrP deposition within the grey, but not white, matter correlated with the degree of astrocytosis for both GFAP and 5HT-2AR and the extent of tissue vacuolation in grey and white matter, although the latter did not correlate with degree of astrocytosis for either GFAP or 5HT-2AR. Astrocytes may be responding directly to the presence of PrP within the tissue, rather than the vacuolar damage to neurones. Although S100beta immunoreactivity was present in astrocytes in control cases, no S100beta staining was seen in astrocytes in either grey or white matter in most CJD cases. There were no differences in the number of TPH-positive cells between CJD and control cases, although the mean TPH-positive cell size was significantly greater, and cells were more intensely stained, in CJD compared to controls, suggesting a pathological overactivity of the brain's serotonergic system in CJD. This may result in excessive release of 5HT within the brain triggering increased 5HT-2AR expression within activated astrocytes leading to release and depletion of S100beta protein from such cells. The clinical symptoms of fluctuating attention and arousal could be mediated, at least in part, by such alterations in function of the serotonergic system.

Purification of recombinant human growth hormone from CHO cell culture supernatant by Gradiflow preparative electrophoresis technology

Purification of recombinant human growth hormone (rhGH) from Chinese hamster ovary (CHO) cell culture supernatant by Gradiflow large-scale electrophoresis is described. Production of rhGH in CHO cells is an alternative to production in Escherichia coli, with the advantage that rhGH is secreted into protein-free production media, facilitating a more simple purification and avoiding resolubilization of inclusion bodies and protein refolding. As an alternative to conventional chromatography, rhGH was purified in a one-step procedure using Gradiflow technology. Clarified culture supernatant containing rhGH was passed through a Gradiflow BF200 and separations were performed over 60 min using three different buffers of varying pH. Using a 50 mM Tris/Hepes buffer at pH 7.5 together with a 50 kDa separation membrane, rhGH was purified to approximately 98% purity with a yield of 90%. This study demonstrates the ability of Gradiflow preparative electrophoresis technology to purify rhGH from mammalian cell culture supernatant in a one-step process with high purity and yield. As the Gradiflow is directly scalable, this study also illustrates the potential for the inclusion of the Gradiflow into bioprocesses for the production of clinical grade rhGH and other therapeutic proteins.

Association of an 11–12 kDa protease-resistant prion protein fragment with subtypes of dura graft-associated Creutzfeldt–Jakob disease and other prion diseases

Creutzfeldt–Jakob disease can develop in subjects given a cadaveric dura mater graft (dCJD). This disease has a phenotypic heterogeneity despite the lack of genetic variation. Numerous plaque-type prion protein (PrP) deposits are found in the brain of some but not all subjects; hence, there may be two subtypes of this clinical entity. To validate dCJD subtypes further, we carried out a larger-scale clinicopathological analysis and typing of protease-resistant PrP (PrPSc) in dCJD cases. Cases with plaque-type PrP deposits (p-dCJD) were shown to be distinct from those without PrP plaques (np-dCJD), from several clinicopathological aspects. Analysis of PrPSc revealed that, while the major PrPSc species from both subtypes was of 21 kDa after deglycosylation (type 1 PrPSc), a C-terminal PrP fragment of 11–12 kDa (fPrP11–12) was associated with np-dCJD but not with p-dCJD. The disease type-specific association of fPrP11–12 was also observed in subjects with other prion diseases. An fPrP11–12-like C-terminal PrP fragment was detected in brain lysates from patients associated with fPrP11–12, but not from patients or normal subjects unassociated with fPrP11–12. Results indicated that fPrP was produced by CJD-associated processes in vivo. The present data provide several lines of evidence that support the need for subtyping of dCJD and contribute to the understanding of the processing of disease-specific PrP species. The unique relationship of fPrP11–12 with CJD phenotype supports the view that the phenotypic heterogeneity of CJD is related to the formation of different types of disease-specific PrP and fragments thereof.

Early cognitive decline in Creutzfeldt-Jakob disease associated with human growth hormone treatment

BACKGROUND

Most cases of Creutzfeldt-Jakob disease (CJD) in recipients of human cadaveric growth hormone present with a cerebellar syndrome. Dementia is thought to occur late and as a minor feature of the illness. However, neuropsychology data published on these cases are largely qualitative and anecdotal. The first published case does include a neuropsychological assessment seven months after the onset of a cerebellar syndrome, showing evidence of intellectual decline. Subsequent reports hint that cognitive problems may be present in the initial stages of the illness.

OBJECTIVE

To assess early cognition in Creutzfeldt-Jakob disease in recipients of pituitary derived human growth hormone.

METHODS

Detailed neuropsychology assessment is reported at referral (mean 4.5 months from the onset of symptoms; range 4 to 6 months) in five patients with histologically proven human growth hormone derived CJD.

RESULTS

All cases presented with a cerebellar syndrome and only one had noticed mild memory problems. On formal testing, however, four had demonstrable mild intellectual decline, as measured on the WAIS-R. One case showed selective visual memory impairment and frontal executive dysfunction.

CONCLUSIONS

These findings suggest that, although not the presenting feature, mild cognitive decline may be evident in the early stages of CJD associated with human cadaveric growth hormone treatment.

Predicting incidence of variant Creutzfeldt-Jakob disease from UK dietary exposure to bovine spongiform encephalopathy for the 1940 to 1969 and post-1969 birth cohorts

BACKGROUND

To investigate variant Creutzfeldt-Jakob disease (vCJD) incubation period, transmission barrier, and short-term vCJD predictions for methionine homozygotes in 1940-1969 and post-1969 birth cohorts by use of gender- and age-specific exposure intensities to bovine spongiform encephalopathy (BSE), based on consumption of beef mechanically recovered meat (MRM) and head meat.

METHODS

Simulation (from vCJD infections generated randomly from gender and age-specific dietary exposure intensities to BSE), constrained to equal the 47 and 64 vCJD onsets before 2001 in 1940-1969 and post-1969 birth cohorts, was used to estimate lognormal (and other) incubation mean and standard deviation which fitted the calendar year distribution of observed vCJD onsets; and to explore exponential decay in susceptibility to infection with age above 15 years.

RESULTS

For the post-1969 birth cohort, the best-fitting lognormal incubation period mean of 11 years (SD 1.5 years and 195 infections) was associated with 194 vCJD onsets (64 before 2001, 105 in 2001-2005, and 25 in 2006-2010). About one-fifth of simulated vCJD onsets before 2001 arose from infections in 1990-1996; age and gender of simulated and observed vCJD patients agreed closely. For the 1940-1969 birth cohort, well-fitting lognormal means ranged widely, the marginally best fitting being 26 years (SD 16.5 years and 382 infections; 47 vCJD onsets before 2001, 58 in 2001-2005, and 63 in 2006-2010). An age-dependent susceptibility function was required to match the age distribution of vCJD patients in the 1940-1969 birth cohort.

CONCLUSIONS

About three-fifths of predicted vCJD onsets are expected to be in males, and nearly two-thirds of vCJD onsets in 2001-2005 are expected to be in post-1969 birth cohort according to best-fitting predictions.

Iatrogenic Creutzfeldt-Jakob disease subsequent to dural graft: persisting risk after 1987

The first case of Creutzfeldt-Jakob disease (CJD) related to the use of a dura mater graft of cadaveric origin was identified in 1987 and this procedure is now considered as one of the main causes of iatrogenic CJD. Although the decontamination procedure for the preparation of graft material was modified, the product was withdrawn from the market in many countries a few years later and replaced by synthetic material. In this context, two patients treated in our institution developed CJD following a cadaveric dural graft performed after cerebral and lumbar trauma. Their clinical presentation, showing predominant cerebellar symptoms, late deterioration and myoclonic jerks, and a rapid disease course until death, was similar to that of previously reported cases involving the iatrogenic form. As the graft for one of the patients was performed in 1991 (several years after modification of the decontamination procedure), this fourth reported case suggests that the risk of iatrogenic CJD may have persisted in some patients treated after 1987, when grafts of cadaveric origin were totally abandoned.

Variant Creutzfeldt-Jakob disease: pathology, epidemiology, and public health implications

Prion diseases, or transmissible spongiform encephalopathies, include Creutzfeldt-Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals. These neurodegenerative diseases are invariably fatal and can be transmitted by inoculation or dietary exposure. They are associated with the accumulation of an altered, disease-associated form of the normal prion protein. Pathologically, prion diseases result in neuronal cell death and a characteristic spongiform appearance of the brain tissue. The emergence of a variant form of CJD (vCJD) in the United Kingdom in 1996 has been causally and experimentally linked to the UK BSE epidemic in the 1980s and early 1990s. The finding that BSE is transmissible to different animal species, unlike previously characterized prion diseases such as sheep scrapie, has raised enormous public health concerns worldwide. Although it is not yet possible to gauge the size of a potential vCJD epidemic, preliminary data indicate a significant dietary exposure to BSE-infected material in Britain and wider implications of the transmissibility of prion diseases. The threat to public health has intensified research efforts to understand the molecular basis of prion diseases, understand their transmission between species, improve methods of diagnosis, and develop therapeutic strategies for treatment and prevention of disease. In this review, we summarize current data on the pathology of BSE and vCJD and the epidemiology of vCJD, and we outline public health implications based on these data, emphasizing preventative measures and areas of research for screening and diagnosis.

Distribution of codon 129 genotype in human growth hormone-treated CJD patients in France and the UK

Since homozygosity MM at codon 129 of the prion protein gene is a recognised risk factor in all forms of Creutzfeldt-Jakob disease (CJD), we studied the distribution of codon 129 polymorphism in patients in France and in the UK with CJD transmitted iatrogenically by human growth hormone. The overall frequencies of codon 129 genotypes in these patients differed from those in the population unaffected by CJD. An excess of VV homozygotes was noted among those with iatrogenic CJD compared with sporadic CJD cases. The proportion of MM genotype in UK patients was surprisingly low (4%) compared with that in French patients (62%). There is no evident explanation for this different distribution, which might be due to infection with different strains of prion in human growth hormone.

Prions and the human transmissible spongiform encephalopathies

The last 5 years have seen the emergence of a new disease in humans (vCJD), mainly in the United Kingdom. This emergence has been accompanied by an explosion of scientific data on a novel group of the responsible infectious agents called prions and has profound implications for infection control and transfusion policies. Also of concern is the finding of prions in neural, gingival, pulpal, and salivary tissue in animal models and significant titers of infectivity from extraneural organs (particularly, in cases of vCJD, in lymphoreticular tissues). There is limited information on the presence of prion proteins in the oral tissues from human studies. Because of the differences in patterns of disease in animal models and in strains of prion protein, it is difficult to extrapolate directly these findings to humans, but it illustrates a potential for transmission by way of the dental route. High levels of infectivity may be present in tissues early in the incubation period and before clinical signs and symptoms. The dental profession must turn its attention to the routine decontamination of dental instruments to ensure that these procedures are performed to the highest regulatory standard. Clinicians and manufacturers must work closely together to develop instruments that are either single use or can be presented in a form that can be more easily decontaminated. Clinicians must pay close attention to manufacturers' decontamination instructions and must not reuse items designated as single use, such as endodontic files. Improvements in compliance with these requirements will not only reduce the risk of transmission of TSEs but also other less tenacious infectious agents.

Variant Creutzfeldt-Jakob disease and its transmission by blood

Variant Creutzfeldt-Jakob disease (vCJD) is a novel acquired human prion disease resulting from human exposure to the agent causing bovine spongiform encephalopathy (BSE). vCJD differs from all other human prion diseases in that the disease-associated form of the prion protein and infectivity are present in lymphoid tissues throughout the body. Lymphoid tissues and lymphocytes are implicated in the peripheral pathogenesis of prion diseases (where infectivity may be detected during the preclinical phase of the illness), giving rise to concerns that blood and blood products may also contain infectivity, thus representing a possible source of iatrogenic spread of vCJD. These concerns have been reinforced by the recent transmission of BSE in an experimental sheep model by blood transfusion from an infected animal in the preclinical phase of the illness. Studies in other animal models suggest that most infectivity in blood may be cell-associated, with lower levels in the plasma, and there is evidence to indicate that any infectivity present may be reduced during the process of plasma fractionation. At present, the attempts to detect disease-associated prion protein and infectivity in buffy coat from vCJD patients have been negative, but these studies have been limited in size and in the sensitivity of the detection systems employed. Further studies are required to develop more sensitive means of detection of disease-associated prion protein in blood; such techniques could also be employed for screening purposes, both individually and to help ascertain more precisely the likely numbers of future cases of vCJD.

What would T. H. Huxley have made of prion diseases?

T. H. Huxley was "Darwin's bulldog," and took the offensive in championing the cause of evolution against skeptical scientists and outraged theologians. As such, he took part in one of the great "paradigm shifts" of biology, at the end of the nineteenth century. Huxley was a rigorous scientist and wrote important articles on scientific method, as well as publishing extensively on a wide range of subjects in natural history. In the second half of the twentieth century, the "prion hypothesis" was put forward to explain the pathogenesis of a curious group of diseases known as the transmissible spongiform encephalopathies. This also involved a "paradigm shift" because the prion hypothesis postulated that biologically relevant information could be enciphered in protein conformation (rather than encoded in nucleic acid base sequences), and could be transmitted from one molecule to another, thereby causing infectious disease. This article examines a few of Huxley's remarks to speculate on how he might have responded to the scientific debate about prion disease had he lived a century later.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

Diagnosis and prevention of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease

An outbreak of bovine spongiform encephalopathy (BSE) arose in the United Kingdom as a result of prions entering and being recycled through the ruminant food chain. Humans have since developed a variant form of Creutzfeldt-Jakob disease (vCJD), also mostly in the United Kingdom, that occurs in younger individuals and causes prominent psychiatric and/or behavioral manifestations early in disease. Laboratory studies now provide strong evidence that the causative agent of BSE in cattle and vCJD in humans share a common origin. Because of a lack of information regarding the incubation period of vCJD and the number of people who may have been exposed, the future scope of this disease remains unknown. Control of the current and any future outbreaks in cattle requires strict measures to prevent contamination of the animal food chain with prions of any species. Prevention of human exposure mandates the avoidance of neural tissue in all human foods.

Use of containment pans and lids for autoclaving caustic solutions

As a means of decontaminating instruments possibly exposed to Creutzfeldt-Jakob disease, the World Health Organization has recommended immersion and autoclaving in sodium hydroxide. However, this recommendation has raised concerns of possible damage to autoclaves, and hazards to operators as a result of the caustic vapors. A series of experiments has been conducted that demonstrate that there are containment pan-and-lid combinations in which instruments can be autoclaved in sodium hydroxide without risk to the autoclave or the operator.

Short-term projections for variant Creutzfeldt-Jakob disease onsets

Projections of both the short- and long-term course of the variant Creutzfeldt-Jakob disease (vCJD) epidemic in Great Britain have demonstrated great uncertainty due to the lack of knowledge of key aspects of the biology and epidemiology of this new disease. Such projections are sensitive to assumptions made regarding the pattern of exposure to BSE-infected animals, the effectiveness of control measures introduced in 1989 and 1996 in reducing this exposure, the functional form of the incubation period distribution and patterns of age-dependent susceptibility/exposure. This paper provides short-term projections for vCJD onsets using the time- and age-distributed onset data to the end of 2000, with results that are directly comparable to the other papers in this issue. These results demonstrate the continued uncertainty in the future scale of this disease.

[The use of disposable instruments of a high performance polymer for tonsillectomy and adenoidectomy]

Cases of the new variant Creutzfeldt-Jakob disease (vCJD) in human beings have to be anticipated in Germany. In subclinical vCJD, the accumulation of prions in lymphoid tissue has been identified prior to their manifestation in cerebral tissue. The remarkable resistance of prions to standard methods of sterilisation questions the safety of reusing metallic surgical instruments. The transmission of vCJD via such reusable surgical instruments in tonsillectomies and adenoidectomies cannot be excluded. In this study, 96 tonsillectomies and adenoidectomies were performed with disposable instruments made of a high performance polymer (Aesculap, Tuttlingen). No increase in the number of intra- or postoperative complications was evident. These disposable instruments may represent an alternative to reusable metallic surgical instruments in potentially infected patients or in patients desiring the use of disposable instruments during their operation for safety reasons.

Mortality trend from sporadic Creutzfeldt-Jakob disease (CJD) in Italy, 1993-2000

The objective was to identify any possible cases of variant Creutzfeldt-Jakob disease (CJD) in Italy, and to estimate the trends in mortality from sporadic CJD for 1993-2000. CJD cases were ascertained through direct notification to the Registry; 382 definite or probable sporadic CJD patients, but no cases of variant CJD were identified. The average yearly mortality rate was 1.04 cases per million inhabitants, with an increase in deaths in the 60-69 and > or =70 year age groups. Survival was shorter in male respect to female and in patients with an age at onset > or =65 years. CJD cases were uneven distributed among different regions in the period 1993-1995, but not herein after. The rise in mortality from sporadic CJD in Italy likely reflects increased awareness and better diagnosis during the years. However, continuous notification and postmortem examination of all suspected cases are recommended for optimal surveillance.

Creutzfeldt-Jakob disease: two case studies

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, neurodegenerative disorder causing dramatic neuromuscular symptoms, profound dementia, and death. In this article, the epidemiology, etiology, modes of transmission, clinical manifestations, determination of possible/probable CJD diagnosis in life, and the postmortem neuropathology of definite CJD are discussed in depth. Case studies of two individuals, each affected by different subtypes of sporadic Creutzfeldt-Jakob disease (sCJD), are presented, along with a discussion of the many challenging nursing and psychosocial issues surrounding the supportive care of these individuals and families in life and death.

Retention of corneal epithelial cells following Goldmann tonometry: implications for CJD risk

AIMS

To assess the adequacy of current decontamination methods for the Goldmann tonometer in the context of variant Creutzfeldt-Jakob disease (vCJD).

METHODS

Reusable Goldmann tonometer prisms were used to perform applanation tonometry on different groups of patients. Following tonometry, retained materials were collected from the tonometer prism head and examined using cytological methods. The used tonometers were subjected to a series of conditions to evaluate their effect on the residual cell numbers found on the tonometer heads. These included wiping alone and wiping or washing followed by disinfection of the tonometer prism. The effect on cell counts of drying the prism overnight was studied, as well as drying overnight and then wiping and disinfecting. All disinfections were performed with sodium hypochlorite (0.05% w/v).

RESULTS

The cytology specimens of 69 patients were studied. Patients using eye drops regularly desquamated significantly more corneal epithelial cells with Goldmann tonometry than patients not using regular eye drops. The mean number of cells was 156 (range 0-470) for patients using eye drops and 14 (4-57) for patients not using eye drops (p = 0.004). Wiping or washing the tonometer head reduced the cell number significantly but neither method completely eliminated cells. The two methods were not significantly different (p=0.3). Drying left a large number of cells (23-320 cells).

CONCLUSIONS

Retained corneal epithelial cells, following the standard decontamination routine of tonometer prisms, may represent potential prion infectivity. Manual cleaning was the most important step in reducing epithelial cell retention.

Updated projections of future vCJD deaths in the UK

BACKGROUND

Past projections of the future course of the vCJD epidemic in the UK have shown considerable uncertainty, with wide confidence bounds. However, recent vCJD case data have indicated a decrease in the annual incidence of deaths over the past two years.

METHODS

A detailed survival model is fitted to the 121 vCJD deaths reported by the end of 2002 stratified by age and calendar time to obtain projections of future incidence. The model is additionally fitted to recent results from a survey of appendix tissues.

RESULTS

Our results show a substantial decrease in the uncertainty of the future course of the primary epidemic in the susceptible genotype (MM-homozygous at codon 129 of the prion protein gene), with a best estimate of 40 future deaths (95% prediction interval 9-540) based on fitting to the vCJD case data alone. Additional fitting of the appendix data increases these estimates (best estimate 100, 95% prediction interval 10-2,600) but remains lower than previous projections.

CONCLUSIONS

The primary vCJD epidemic in the known susceptible genotype in the UK appears to be in decline.

Factors determining the pattern of the variant Creutzfeldt-Jakob disease (vCJD) epidemic in the UK

Following the emergence of a new variant of Creutzfeldt-Jakob disease (vCJD) 6 years ago, and the gradual rise in clinical cases, there has been increased speculation regarding the overall magnitude of this epidemic in Great Britain. In this paper, we explore the epidemiological factors and uncertainties determining the scale of this epidemic in light of the most recent data on reported vCJD mortality. Our results demonstrate that, while the magnitude of the uncertainty has decreased dramatically since 1996, it is still not possible to predict with any degree of accuracy the final magnitude of this epidemic, with the 95% confidence interval for future cases being from 10 to 7000 deaths. However, short-term projections show that it is unlikely that a dramatic increase in case numbers will be observed in the next 2-5 years (95% confidence interval for 2 years: 10-80 cases, for 5 years: 10-200 cases). The results confirm significant age-dependent susceptibility/exposure to infection, with the likelihood profile demonstrating that those aged between 10 and 20 years are at highest risk of infection. We also demonstrate how projections based on onset data may be substantially biased, and explore the sensitivity of results to assumptions concerning the exposure to bovine spongiform encephalopathy (BSE) and the incubation-period distribution.

Variant Creutzfeldt-Jakob disease

Variant CJD is a novel human prion disease that represents the first known occasion in which animal prion diseases have been transmitted to humans. There are many uncertainties concerning vCJD, including the mechanism of transmission between species, the extent of human exposure to the BSE agent, the infectious dose for humans, and the future burden of human disease. It is hoped that continuing scientific research may lead to answers to some of these questions and that further understanding of the mechanism of prion replication may lead to the development of effective treatment. Indeed a recent publication has suggested that the drugs quinacrine or chloropromazine may be candidates for the treatment of human prion diseases [42].

Transmissible spongiform encephalopathy update and implications for blood safety

At this time, the accumulated evidence does not support the implementation of measures targeted against the risk of transfusion transmission of sporadic, familial, or iatrogenic CJD. Evolving information about vCJD, however, suggests that policy makers need to consider implementing measures to protect against exposure to vCJD, if such measures themselves do not lead to decreased blood safety. Surveillance of human TSEs and investigation of the risk of transfusion transmission must continue in order to provide further refinements in blood safety policy.

Disease latency in Creutzfeldt-Jakob disease via dural grafting: a case report

The case of a 57-year old man is reported who had been operated upon for cerebellar angioblastoma more than 19 years previously. Having received a lyophilized dural patch he developed Creutzfeldt-Jakob disease of which he died 19 months later. This is the longest latency with dura-associated Creutzfeldt-Jakob disease reported so far.

[Prion diseases]

Prion is an ubiquitous membrane protein in mammals, which is mainly synthesized in central nervous system. Prion diseases are the result of an accumulation of prions having acquired a resistance to the physiological degradation and an infectious capacity. Human prion diseases are very rare diseases including sporadic Creutzfeldt-Jakob disease (the most frequent form manifesting as a presenile dementia), familial transmissible spongiform encephalopathies and two juvenile transmissible forms: iatrogenic Creutzfeldt-Jakob secondary to treatment with human extractive growth hormone and variant Creutzfeldt-Jakob disease resulting from bovine spongiform encephalopathy food transmission. Knowledge of the underlying prion biology has led to preventive measures which offer today a reasonable guarantee against the juvenile forms.

Subclinical prion infection in humans and animals

Transmission of prion diseases between mammalian species is limited by a so-called 'species' or 'transmission' barrier. Recognition of prion transmission usually relies on the appearance of clinical symptoms in inoculated animals and the interval between inoculation and appearance of clinical disease is designated incubation period. At some point during this clinically silent period, neuropathological and biochemical changes as well as accumulation of prions in the brain can be detected and this stage can be called preclinical prion disease. Recently, several lines of evidence have suggested that subclinical forms of prion disease exist, in which high levels of infectivity and PrP(Sc) are found in animals that do not develop clinically apparent disease during a normal life-span. Such asymptomatic prion 'carrier' states challenge our current understanding of pathogenesis as well as of the molecular basis of barriers to transmission. Subclinical as well as preclinical/clinical prion disease may be relevant when analysing the risk to public health of potential sources of prion exposure.

Prions and the immune system: a journey through gut, spleen, and nerves

For more than two decades it has been contended that prion infection does not elicit immune responses: transmissible spongiform encephalopathies do not go along with conspicuous inflammatory infiltrates, and antibodies to the prion protein are typically undetectable. Why is it, then, that prions accumulate in lymphoid organs, and that various states of immune deficiency prevent peripheral prion infection? This review revisits the current evidence of the involvement of the immune system in prion diseases, while attempting to trace the elaborate mechanisms by which peripherally administered prions invade the brain and ultimately cause damage. The investigation of these questions leads to unexpected detours, including the neurophysiology of lymphoid organs, and even the function of a prion protein homolog in male fertility.

Acquired prion disease: iatrogenic CJD, variant CJD, kuru

Human prion diseases can be classified as sporadic, hereditary or acquired. The cause of sporadic Creutzfeldt-Jakob disease (CJD) is unknown, hereditary cases are associated with mutations of the prion protein gene (PRNP) and acquired forms are caused by the transmission of infection from human to human or, as a zoonosis, from cattle to human. Although acquired forms of human prion disease are rare, the transmission of a fatal and untreatable neurological disorder has had major implications for public health and public policy.

[Hygenic measures for Creutzfeldt-Jakob disease]

The Creutzfeldt-Jakob disease (CJD) belongs to the so-called prion diseases or transmissible spongiform encephalopathies. The iatrogenic transmission of the pathogen by direct contact with infectious tissue, tissue extracts and surgical instruments has been demonstrated. CJD is not an infectious disease in the usual sense. Transmission is not possible by normal social contact nor by nursing measures just as CJD can not be transferred by normal skin contact or contact with blood, serum or other patient' secretions. Therefore, CJD patients do not have to be isolated, because strict conformity to the generally recognized rules of hygiene is completely sufficient. The high resistance of prions to environmental influences requires the combination of different disinfection and sterilization measures before inactivation of the pathogen occurs and it is possible to exclude transmission by medical products.

Molecular and clinical classification of human prion disease

While rare in humans, the prion diseases have become an area of intense clinical and scientific interest. The recognition that variant Creutzfeldt-Jakob disease is caused by the same prion strain as bovine spongiform encephalopathy in cattle has dramatically highlighted the need for a precise understanding of the molecular biology of human prion diseases. Detailed clinical, pathological and molecular data from a large number of human prion disease cases have shown that distinct abnormal isoforms of prion protein are associated with prion protein gene polymorphism and neuropathological phenotypes. A molecular classification of human prion diseases seems achievable through characterisation of structural differences of the infectious agent itself.

Transmission of prions

The "protein only" hypothesis states that the infectious agent causing transmissible spongiform encephalopathies is a conformational isomer of PrP, a host protein predominantly expressed in brain, and is strongly supported by many lines of evidence. Prion diseases are so far unique among conformational diseases in that they are transmissible, not only experimentally but also by natural routes, mainly by ingestion. A striking feature of prions is their extraordinary resistance to conventional sterilization procedures, and their capacity to bind to surfaces of metal and plastic without losing infectivity. This property, first observed in a clinical setting, is now being investigated in experimental settings, both in animals and in cell culture.

Diffusion-weighted sequence on MRI for the diagnosis of Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) is a progressive and fatal dementing illness caused by a virus like agent called prion. Currently, the definitive diagnosis can only be made through brain biopsy. Given its potential transmissibility, it is paramount to have noninvasive and reliable means to detect the disease. The present case reports on a 63 year-old man with biopsy proven CJD, and evaluates the dependability of diffusion-weighted MRI in this condition, stressing the importance of this particular sequence to its diagnosis.

Transmission of prions

The "protein only" hypothesis holds that the infectious agent causing transmissible spongiform encephalopathies is a conformational isomer of PrP, a host protein that is predominantly expressed in the brain. This hypothesis is strongly supported by many lines of evidence. To date, prion diseases are unique among conformational diseases in that they are transmissible-experimentally and by natural routes (mainly by ingestion). The pathway of prions to the brain has been elucidated in outline. A striking feature of prions is their extraordinary resistance to conventional sterilization procedures and their capacity to bind to surfaces of metal and plastic without losing infectivity. This property, first observed in a clinical setting, is now being investigated in experimental settings, both in animals and in cell culture.

A French cluster of Creutzfeldt-Jakob disease: a molecular analysis

We report the molecular and phenotypic analysis of a French cluster of three cases of Creutzfeldt-Jakob disease (CJD), two of them occurring in 1998 in the same village and the other in 1995 in a neighboring village. Analyses of the occurrence of these events in a close area with less than 3000 inhabitants over the 1992-1999 notification period confirmed that they are rare. This could be explained either by a common source of contamination or by the coincidental occurrence of either sporadic or genetic CJD. We applied genetic analysis and brain PrPres typing to explore these CJD cases. The three patients did not carry any mutation in their prion protein gene coding sequence. All were homozygous for methionine at the polymorphic codon 129. Brain tissue was available from two cases that died in 1998. The two patients showed different PrPres profiles on Western blot and distinct clinico-pathological features. These findings do not support the conclusion that in these three cases, CJD was acquired from a unique source of contamination and suggest that concurrent occurrence of sporadic CJD accounted for this CJD cluster.

Studies on the removal of a bovine spongiform encephalopathy-derived agent by processes used in the manufacture of human immunoglobulin

BACKGROUND AND OBJECTIVES

There is still uncertainty over how the agent of variant Creutzfeld-Jakob disease (vCJD) would partition during the manufacture of plasma derivatives. In this study, a BSE-derived agent was used as a vCJD model to determine the extent to which infectivity could be removed by selected steps used in the manufacture of intravenous immunoglobulin (IVIG).

MATERIALS AND METHODS

Murine-passaged BSE (strain 301V), in the form of a microsomal fraction prepared from infected brain, was used to "spike" the starting material in three experiments. The partitioning of BSE infectivity was measured over Fraction I+III precipitation, borosilicate microfibre depth filtration and Seitz depth filtration, with these steps being examined individually and in series.

RESULTS

Most 301V infectivity partitioned into Fraction I+III (log reduction 2.1). Infectivity remaining in Supernatant I+III was reduced by AP20 glass-fibre depth filtration (log reduction 0.6) and subsequently removed to below the limit of detection by Seitz KS80 depth filtration, giving an overall log reduction of > or = 2.9 for the three steps in series. By contrast, glass-fibre depth filtration gave a log reduction of 2.4 when challenged directly with "spiked" feedstock. Seitz KS80 depth filtration gave a log reduction of > or = 3.1 when challenged directly with 'spiked' feedstock and also removed residual infectivity to below the limit of detection when applied as the final step in series.

CONCLUSIONS

Results using a BSE-derived agent suggest that vCJD infectivity should be substantially removed from immunoglobulin G (IgG) solutions by Fraction I+III precipitation and Seitz KS80 depth filtration. The three different process steps examined acted in a complementary manner to one another when operated in series. However, the data demonstrated that it would be inappropriate to add together the reduction factors that had been derived for each step in isolation.

Managing the risk of nosocomial transmission of prion diseases

PURPOSE OF REVIEW

Prion diseases such as Creutzfeldt-Jakob disease represent a unique infection control problem because prions exhibit an unusual resistance to conventional chemical and physical decontamination methods. This paper reviews the recent literature and provides recommendations for the prevention of nosocomial transmission of prion agents.

RECENT FINDINGS

Recommendations to prevent the cross-transmission of infection from medical devices potentially contaminated with prions have been based primarily on prion inactivation studies. Newer recommendations consider inactivation data, but also use epidemiological studies of prion transmission, the infectivity of human tissues, and the efficacy of removing microbes by cleaning. Prion-specific disinfection/sterilization is required in only limited settings. Healthcare workers are not at risk of acquiring transmissible spongiform encephalopathies. Blood or blood products have not been demonstrated to be vehicles for transmission.

SUMMARY

On the basis of scientific data, only critical (e.g. surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e. brain, spinal cord, eye) from high-risk patients (e.g. with known or suspected Creutzfeldt-Jakob disease) require special treatment.

Variant Creutzfeldt-Jakob disease--a problem for general dental practitioners?

Over a hundred deaths from variant Creutzfeldt-Jakob disease (vCJD) have now been recorded. The incubation period for vCJD may be up to 40 years and the number of asymptomatic carriers in the population could be as many as 100,000. Confirmed iatrogenic transmission of other human transmissible spongiform encephalopathies raises the possibility of cross-infection from apparently healthy persons who are incubating vCJD. Decontamination techniques routinely used in general dental practice are incapable of inactivating the infective protein responsible for transmitting the disease. So far, no evidence exists to preclude the risk of iatrogenic infection occurring during dental procedures. The author reviews present knowledge of the infective agent, its transmissibility, its origins, current guidelines and the implications for dental practice.

Creutzfeldt-Jakob disease cluster in an Australian rural city

Through the Australian National Creutzfeldt-Jakob Disease Registry, 6 pathologically confirmed sporadic cases were recognized over a 13-year period in persons who had been long-term residents of a moderate-sized rural city, whereas the expected number was 0.923. An extensive investigation could not find any point-source or case-to-case transmission links. This occurrence is highly statistically significant (p = 0.0027) when viewed in isolation and remains significant (p < 0.02) when only the cases that arose after the cluster was recognized were taken into account. However, a more conservative statistical analysis suggests that such a grouping could have arisen by chance in at least one population group of this size when the whole country is taken into consideration.

Kuru: the old epidemic in a new mirror

The kuru epidemic lasted almost a century; it started in 1901-1902, reached epidemic proportions in the mid-1950s, and disappeared in the 1990s. Kuru is the prototype member of a group of disorders known as transmissible spongiform encephalopathies (TSEs) or prion diseases. Recent data on the genetics and pathogenesis of TSEs contribute to a better understanding of the documented kuru phenomena, and vice versa, observations made during the kuru epidemic are immensely helpful in understanding the epidemic of variant Creutzfeldt-Jakob disease that is currently developing in Europe. The major goal of this review is to identify and illustrate these points.