Bovine Spongiform Encephalopathy

Abstract

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease of cattle caused by foodborne exposure to prions. First described in 1986, this novel disorder was clinically characterized by altered behavior, sensory changes, and locomotor signs. For almost two decades, BSE, now named classical BSE (C-type BSE), has been regarded as the only and exclusive prion disorder of cattle. The introduction of an active surveillance system for BSE in 2001 allowed the identification of two additional atypical forms of BSE, named H-type and L-type BSEs, because of distinct conformations of the pathological prion protein, or PrP^Sc, with higher (H-type) or lower (L-type) electrophoretic mobility of the unglycosylated protease-resistant PrP^Sc fragment. To date, a total of 34 L-type BSE and 27 H-type BSE have been detected worldwide by routine BSE testing in older cattle. The clinical phenotypes of atypical BSE forms are still undefined in field animals, although information has been obtained from intraspecies transmission studies. Transmission studies to mice show that C-type, H-type, and L-type BSE forms display distinct molecular properties, consistent with the occurrence of three different prion strains. Intriguingly, upon serial passages, H-type and L-type BSEs may acquire C-type properties, hence suggesting a possible role in the origin of BSE epidemics. Further, the evidence that atypical BSEs are transmissible to mammals, including nonhuman primates, are issues that raise public health concerns.