Diagnosis of transmissible spongiform encephalopathies in ruminants

Abstract

The diagnosis of transmissible spongiform encephalopathies (TSE) in ruminants relies on the detection of PrPres, the proteinase K (PK)-resistant pathological isoform of the prion protein. The latter can be detected in situ by immuno-histochemical methods, or by immunological methods following extraction from tissues and PK treatment (Western-blot, Enzyme Linked ImmunoSorbent Assay). Although considerable progress has been made in recent years in routine TSE diagnosis, it remains a post-mortem detection that is only possible in brain tissues from adult animals in which sufficient amounts of PrPres have accumulated. Tonsil biopsies allow an ante-mortem diagnosis only in animals whose lymphoid tissues contain PrPres, i.e. sheep of susceptible genotypes and goats. Other methods are currently being explored : these are aimed at detecting in the blood either PrPres or a marker specifically expressed during the incubation period. In addition, a search is currently under way for tests that could distinguish strains of TSE, or specifically recognise the bovine spongiform encephalopathy strain. Such improvements should represent a considerable progress towards a better understanding of TSE transmission and epidemiology, which in turn may help in defining new prevention strategies.