Phenotype-genotype studies in kuru: implications for new variant Creutzfeldt-Jakob disease

Variant Creutzfeldt-Jakob disease: immunocytochemical studies and image analysis

Variant Creutzfeldt-Jakob disease (vCJD) is a recently identified human prion disease that appears to arise from exposure to the bovine spongiform encephalopathy agent. The clinical features and neuropathology of vCJD are distinctive, particularly the patterns of PrP(sc) accumulation in the brain. PrP immunocytochemistry has also demonstrated the accumulation of PrP(sc) in tissues outside the central nervous system, including sensory ganglia and lymphoid tissues. These observations have allowed the use of tonsillar biopsy as an investigation to aid the diagnosis of vCJD, since accumulation of PrP(sc) in lymphoid tissues does not occur in other forms of human prion disease. The patterns of PrP(sc) accumulation in vCJD can be studied by image analysis techniques, using both quantitative and qualitative approaches. Preliminary results of textural analysis are presented, which indicate that this approach can be used to discriminate and study the unique features of PrP(sc) accumulation in the brain in vCJD. This technique has major potential as a research tool in human prion diseases, particularly for the characterisation of disease phenotype in large series of cases.

Creutzfeldt-Jakob disease, new variant creutzfeldt-jakob disease, and bovine spongiform encephalopathy

Creutzfeldt-Jakob disease (CJD) is a subacute spongiform encephalopathy (SSE) that is manifested by a variety of neurologic signs that usually include dementia, myoclonus, and an abnormal electroencephalogram (EEG). In 1996, a new variant of CJD (nvCJD) with a somewhat distinctive clinical presentation and neuropathology was reported in adolescents and young adults, a cohort of patients not normally affected with CJD. The appearance of nvCJD coincided temporally and geographically with the emergence of an SSE in cattle known as bovine spongiform encephalopathy (BSE), or mad cow disease. This article discusses the clinical syndrome, pathology, and pathogenesis of classical CJD, nvCJD, and other human SSEs, as well as the link between BSE and nvCJD.

Oral transmission and early lymphoid tropism of chronic wasting disease PrPres in mule deer fawns (Odocoileus hemionus)

Mule deer fawns (Odocoileus hemionus) were inoculated orally with a brain homogenate prepared from mule deer with naturally occurring chronic wasting disease (CWD), a prion-induced transmissible spongiform encephalopathy. Fawns were necropsied and examined for PrPres, the abnormal prion protein isoform, at 10, 42, 53, 77, 78 and 80 days post-inoculation (p.i.) using an immunohistochemistry assay modified to enhance sensitivity. PrPres was detected in alimentary-tract-associated lymphoid tissues (one or more of the following: retropharyngeal lymph node, tonsil, Peyer's patch and ileocaecal lymph node) as early as 42 days p.i. and in all fawns examined thereafter (53 to 80 days p.i.). No PrPres staining was detected in lymphoid tissue of three control fawns receiving a control brain inoculum, nor was PrPres detectable in neural tissue of any fawn. PrPres-specific staining was markedly enhanced by sequential tissue treatment with formic acid, proteinase K and hydrated autoclaving prior to immunohistochemical staining with monoclonal antibody F89/160.1.5. These results indicate that CWD PrPres can be detected in lymphoid tissues draining the alimentary tract within a few weeks after oral exposure to infectious prions and may reflect the initial pathway of CWD infection in deer. The rapid infection of deer fawns following exposure by the most plausible natural route is consistent with the efficient horizontal transmission of CWD in nature and enables accelerated studies of transmission and pathogenesis in the native species.

Epidemiological determinants of the pattern and magnitude of the vCJD epidemic in Great Britain

Understanding the epidemiology and aetiology of new-variant Creutzfeldt-Jakob (vCJD) disease in humans has become increasingly important given the scientific evidence linking it to bovine spongiform encephalopathy (BSE) in cattle and hence the wide exposure of the population of Great Britain (GB) to potentially infectious tissue. The recent analysis undertaken to determine the risk to the population from dorsal route ganglia illustrated the danger in presenting point estimates rather than ranges of scenarios in the face of uncertainty. We present a mathematical template that relates the past pattern of the BSE epidemic in cattle to the future course of any vCJD epidemic in humans, and use extensive scenario analysis to explore the wide range of possible outcomes given the uncertainty in epidemiological determinants. We demonstrate that the average number of humans infected by one infectious bovine and the incubation period distribution are the two epidemiological factors that have the greatest impact on epidemic size and duration. Using the time-series of the BSE epidemic and the cases seen to date, we show that the minimum length of the incubation period is approximately nine years, and that at least 20% of the cases diagnosed to date were exposed prior to 1986. We also demonstrate that the current age distribution of vCJD cases can only arise if younger people were either exposed to a greater extent, more susceptible to infection, or have shorter incubation periods. Extensive scenario analyses show that given the information currently available, the very high degree of uncertainty in the future size of the epidemic will remain for the next 3-5 years. Furthermore, we demonstrate that this uncertainty is unlikely to be reduced by mass screening for late-stage infection.