Experimental scrapie in white Swiss mice.

In order to confirm the clinical and histological diagnosis of scrapie and to determine the infectivity titer of the scrapie agent in the brain of a naturally infected Suffolk sheep, 123 white Swiss mice were inoculated intracerebrally. From about 13 to 20 months post-inoculation, 28 mice died, and 95 that were sick were killed. In the terminal stages of disease, the mice developed weakness, gradual emaciation, posterior ataxia, and occasionally alopecia. The average infection (83%) of mice affected with scrapie occurred in groups 1 to 4 inoculated with dilution 10(-1) to 10(-4) of scrapie sheep brain. Sixty-seven (54.5%) of the mice developed spongiform lesions and vacuolar degeneration of neurons. Similarities of scrapie with other subacute spongiform encephalopathies in animals and humans are discussed.