Experimental Bovine Spongiform Encephalopathy: Detection of PrPSc in the Small Intestine Relative to Exposure Dose and Age.

Summary: European regulations for the control of bovine spongiform encephalopathy (BSE) decree destruction of the intestines from slaughtered cattle, therefore producers have been obliged to import beef casings from countries with a negligible BSE risk. This study applies immunohistochemical and biochemical approaches to investigate the occurrence and distribution of disease-associated prion protein (PrP^Sc) in the duodenum, jejunum and ileum of cattle orally exposed to a 1g or 100g dose of a titrated BSE brainstem homogenate. Samples were derived from animals at various times post exposure. Lymphoid follicles were counted and the frequency of affected follicles recorded. No PrP^Sc was detected in the duodenum or jejunum of animals exposed to a 1g dose or in the duodenum of animals receiving a 100g dose. PrP^Sc was detected in the lymphoid tissue of the ileum of 1/98 (1.0%) animals receiving the 1g dose and in the jejunum and ileum of 8/58 (13.8%) and 45/99 (45.5%), respectively, of animals receiving the 100g dose. The frequency of PrP^Sc- positive follicles was less than 1.5% per case and biochemical tests appeared less sensitive than immunohistochemistry. The probability of detecting lymphoid follicles in the ileum declined with age and for the 100g exposure the proportion of positive follicles increased, while the proportion of positive animals decreased with age. Detection of PrP^Sc in intestinal neural tissue was rare. The results suggest that the jejunum and duodenum of BSE-infected cattle contain considerably less BSE infectivity than the ileum, irrespective of exposure dose. In animals receiving the low exposure dose, as in most natural cases of BSE, the rarity of PrP^Sc detection compared with high-dose exposure, suggests a very low BSE risk from food products containing the jejunum and duodenum of cattle slaughtered for human consumption. [ABSTRACT FROM AUTHOR]