Fig. 2.

Transgenic mouse bioassay of scrapie. Shown are the outcomes following intracerebral inoculation of Tg338 (a) or TgElk (b) mice with scrapie prions derived from sheep S3178 and goats G3538, G3558, G3953 and G30-75. Closed circles, mice culled at the onset of clinical disease and PrP^res detected in the brain; open circles, preclinical mice (culled due to intercurrent health issues or during the endpoint period with no clinical signs but PrP^res detected in the brain); open squares, mice with no detectable PrP^res in the brain at the time of cull. Censored data are included. Though variable in survival time, nearly all Tg338 mice inoculated with sheep brain homogenate harbouring classical scrapie prions developed clinical disease, whereas none of the TgElk mice similarly inoculated developed clinical disease.