[Prions: where do we stand 20 years after the appearance of bovine spongiform encephalopathy?]

Mathematical Models for Estimating the Risks of Bovine Spongiform Encephalopathy (BSE)

When the bovine spongiform encephalopathy (BSE) epidemic first emerged in the United Kingdom in the mid 1980s, the etiology of animal prion diseases was largely unknown. Risk management efforts to control the disease were also subject to uncertainties regarding the extent of BSE infections and future course of the epidemic. As understanding of BSE increased, mathematical models were developed to estimate risk of BSE infection and to predict reductions in risk in response to BSE control measures. Risk models of BSE-transmission dynamics determined disease persistence in cattle herds and relative infectivity of cattle prior to onset of clinical disease. These BSE models helped in understanding key epidemiological features of BSE transmission and dynamics, such as incubation period distribution and age-dependent infection susceptibility to infection with the BSE agent. This review summarizes different mathematical models and methods that have been used to estimate risk of BSE, and discusses how such risk projection models have informed risk assessment and management of BSE. This review also provides some general insights on how mathematical models of the type discussed here may be used to estimate risks of emerging zoonotic diseases when biological data on transmission of the etiological agent are limited.

[Prion diseases: what is the role of dendritic cells in the pathogenesis of transmissible prion diseases?]

Prion diseases are caused by the transconformation of a normal cellular protein, PrPc, into an infectious isoform, PrPsc, which ultimately triggers neuronal death. They are always fatal and, after transmission, they feature long incubation periods, during which prions accumulate in lymphoid tissues, infect nerves and progress to the central nervous system. In lymphoid organs, prions replicate and accumulate in follicular dendritic cells. Suppressing these cells slows down the neuro-invasion but does not totally abrogate it. This review examines the current knowledge in the roles of hematopoietic dendritic cells at different steps of the pathogenesis of prion diseases. Dendritic cells endocytose inoculated prions, permit their crossing of the intestinal epithelium and then migrate and transport them to lymphoid organs. They can carry prions to sites of neuroinvasion, and establish contacts with axons in peripheral lymph nodes or even after passage of the blood-brain barrier. However, results in the literature on the role of dendritic cells differ according to the host or the prion strain.

[Food safety and animal diseases. The French Food Safety Agency, from mad cow disease to bird flu]

Why has the French food safety agency been particularly mobilized on zoonoses like bovine spongiform encephalopathy ("mad cow disease") or highly pathogenic avian influenza ("bird flu") ? Because sanitary crisis make explicit an ambivalent relationship between humans and animals (animals being perceived alternatively as providers of goods and as bearers of threats), and to the circulation of life in general (the contaminated blood crises being due to the rapprochement of blood giving and blood receiving). The sociology of risks needs therefore to reintegrate the idea of an intention of the risk bearer (risk with enemy), and the sociology of alimentation needs to reintegrate the analysis of the conditions of production. Mad cow disease is the paradigmatic food safety crisis because it brings together the poles of production and consumption, of animals and humans. It therefore belongs to anthropology.