ARS | Publication request: Identification and Characterization of U.S. Bse Cases

Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract
Publication Acceptance Date: August 1, 2006
Publication Date: October 12, 2006
Citation: Hall, S.M., Richt, J., Davis, A., Kluge, J., Simmons, M., Stack, M., Spencer, Y. 2006. Identification and characterization of U.S. BSE cases [abstract]. American Association of Veterinary Laboratory Diagnosticians. p. 56.

Technical Abstract: Bovine Spongiform Encephalopathy (BSE) surveillance has been ongoing in the USA since the early 1990's and initial testing was done at the USDA, National Veterinary Services Laboratories (NVSL) utilizing routine histopathology exclusively. In 1995, the immunohistochemistry (IHC) test was incorporated into surveillance testing in addition to routine histopathology. By 1999 virtually all BSE screening was performed by IHC and by 2001 the NVSL had switched to an automated IHC procedure. In 2002 and 2003 the NVSL tested about 20,000 high risk animals each year by IHC. In December, 2003 an animal was identified by IHC as positive for BSE (Case 1); this animal was determined to be imported from Canada. After this animal was identified, in June 2004 the USDA began its enhanced surveillance program as a shared effort between selected state veterinary diagnostic laboratories and NVSL, as part of the National Animal Health Laboratory Network. The plan called for testing as many targeted high risk animals as possible in a 12-18 month period. From June 1, 2004 through March 21, 2006, over 650,000 animals have been tested (Bio-Rad ELISA). Of those tested, two animals (Cases 2 and 3) have been identified as positive for BSE. While all three cases were strongly positive by Bio-Rad ELISA, Cases 2 and 3 have common features which are distinct from Case 1. Definitive spongiform changes in the obex, strong immunohistochemical reactions, and Western blot patterns similar to European BSE cases were observed in Case 1. In contrast, Cases 2 and 3 did not contain definitive histological lesions of BSE and the IHC staining was less intense than Case 1. In addition, Cases 2 (approximately 12 years) and Case 3 (approximately ten years) were older animals while Case 1 was 6.5 years old. Western blot analysis, PrP**Sc from Case 1 showed molecular features similar to typical BSE isolates, whereas PrP**Sc from Cases 2 and 3 revealed an unusual molecular PrP**Sc pattern: molecular mass of the unglycosylated and monoglycosylated isoform was higher than that of typical BSE isolates. Case 1 contained more PrP**Sc per brain tissue mg equivalent compared with Cases 2 and 3 using antibody 6H4. In Western Blot analysis, Case 2 and Case 3 were strongly positive with antibody P4, while Case 1 was negative or weakly positive with P4.