Bovine Spongiform Encephalopathy: Investigation of Phenotypic Variation among Passive Surveillance Cases M. J. Stack * , S. J. Moore * , A. Davis † , P. R. Webb * , J. M. Bradshaw ‡ , Y. H. Lee x , M. Chaplin * , R. Focosi-Snyman * , L. Thurston * , Y. I. Spencer * , S. A. C. Hawkins * , M. E. Arnold * , M. M. Simmons * and G. A. H. Wells * *Veterinary Laboratories Agency, Woodham Lane, Addlestone, Surrey KT15 3NB, UK, † Dorevitch and Gippsland Vetnostics, 267 Moreland Road, Coburg, Victoria 3058, Australia, ‡ Veterinary Laboratories Agency, Langford House, Langford, Bristol BS40 5DX, UK and x Foreign Animal Disease Division, National Veterinary Research and Quarantine Service, Republic of Korea Summary Bovine spongiform encephalopathy (BSE) is a prion disease of domesticated cattle, first identified in Great Britain (GB) in 1986. The disease has been characterized by histopathological, immunohistochemical, bio- chemical and biological properties, which have shown a consistent disease phenotype among cases obtained by passive surveillance. With the advent of active surveillance in 2001, immunological tests for detection of the prion protein revealed some cases with different biochemical characteristics and, in certain instances, dif- ferences in pathology that have indicated variant phenotypes and the possibility of agent strain variation. This study examines a case set of 523 bovine brains derived from archived material identified through passive sur- veillance in GB. All cases conformed to the phenotype of classical BSE (BSE-C) by histopathological, immu- nohistochemical and biochemical approaches. The analyses consolidated an understanding of BSE-C and, by western blotting, confirmed differentiation from the known atypical BSE cases which exhibit higher or lower molecular masses than BSE-C (BSE-H and BSE-L respectively). Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved. Keywords: bovine spongiform encephalopathy; immunohistochemistry; phenotype variation; western blotting Introduction Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disor- ders affecting a wide range of mammalian hosts and include kuru and CreutzfeldteJakob disease (CJD) in man, scrapie in sheep and goats and bovine spongi- form encephalopathy (BSE) in cattle (H€ ornlimann et al., 2006). BSE was first described in 1986 in Great Britain (GB) (Wells et al., 1987), emerged as a feed- borne epidemic and, a decade later, was causally linked to the occurrence of a new form of human prion disease, new variant CJD (vCJD) (Collinge et al., 1996; Lasm ezas et al., 1996; Will et al., 1996; Bruce et al., 1997; Hill et al., 1997). Due to the novel and uncertain nature of the causal agent of TSEs, the characterization of these disorders has been based on phenotypic features. In the early years of the BSE epidemic, the case definition of BSE was reliant on histopathological characterization and diagnosis was based principally on detection of vacuolation in the brain stem of clini- cally suspect cattle (Wells et al., 1989). This was sup- plemented with the examination of brain tissue by electron microscopy for disease-associated scrapie-as- sociated fibrils (SAFs) comprised of a disease-associ- ated protein, characterized as PrP or prion protein (Hope et al., 1988; Scott and Stack 1994; Stack et al., 1996). Biological characterization of a small number of individual isolates by transmission from affected brain to mice indicated that the cases were attributable to a single strain of agent that differed Correspondence to: M. J. Stack (e-mail: m.j.stack@vla.defra.gsi.gov.uk). 0021-9975/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jcpa.2010.10.007 J. Comp. Path. 2011, Vol. 144, 277e288 Available online at www.sciencedirect.com www.elsevier.com/locate/jcpa