This possibly explains the massive buildup in numbers of positive cattle in England over 6 years and the persistent low level infection still seen after years of prohibiting the feeding of mammalian protein sources. There has not been a direct correlation between any of the TSE diseases of animals and that of man. Scientists have been concerned about a variant form of CJD that has become more prevalent since the mad cow crisis. A strong correlation to eating beef has not been established. No tests are presently available for use on a living animal.
Research is ongoing in Europe for such tests.
Microscopic examination of brain tissue is the most common method now in use. The feeding of rendered animal products of US origin to ruminants has been tightly regulated since 1997. Renderers and feed mills are under federal inspection for compliance. Importation of animals or animal by-products has been tightly controlled since 1986. Suspicious neurological cases are examined for evidence of BSE at slaughter.