Unfortunately, the slaughter of the great majority of affected animals becomes necessary at an early stage because of unmanageable behavior and injury from repeated falling and uncontrollable behavior (Cowell, 1996). The duration of the clinical disease, from the earliest signs to death or slaughter, can range from under two weeks to as long as a year. The average period is about one to two months (Lyall, 1996).
BSE resembles other members of the scrapie family in not having any gross pathological lesions associated with disease. Characteristic histo-
pathological changes are found in the nervous system (Kimberlin, 1993). In common with the other diseases in the scrapie family, BSE has a distinctive non-inflammatory pathology with three main features.
The most important diagnostic lesion is the presence of bilaterally symmetrical neuronal vacuolation, in processes and in soma.
Hypertrophy of astrocytes often accompanies vacuolation.
Cerebral amyloidosis is an inconstant histopathological feature of the scrapie family of diseases.
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