Two tests have already been carried out on the cow enabling Agriculture Secretary Ann Veneman to call the case a "presumptive positive" and a sample is being flown to England for a third test to absolutely confirm the case.

Bovine spongiform encephalopathy, or BSE, is linked to a similar form of the incurable and fatal brain-wasting disease in humans, called variant Creutzfeldt-Jakob Disease, or vCJD. There have been a small number of cases of vCJD reported worldwide, primarily in the United Kingdom, in people who ate BSE-contaminated meat.
Officials believe that meat from the Washington animal left a processing plant, Veneman said, and an investigation is under way to determine if any had reached store shelves.
http://www.cnn.com/2003/US/12/23/mad.cow/index.html