Experimental infection of cattle with the agents of transmissible mink encephalopathy and scrapie

Cattle are susceptible to experimental infection with the Stetsonville isolate of the transmissible mink encephalopathy (TME) agent. To determine if they are susceptible to other TME isolates, two groups of calves were inoculated intracerebrally with homogenate of mink brain containing the Hayward isolate or the Blackfoot isolate. For comparison, a third group was inoculated with a brain homogenate from a steer infected with the Stetsonville isolate in its primary cattle passage and a fourth group was inoculated with a pool of brain homogenate from three cattle experimentally infected with a sheep and goat scrapie agent in its primary cattle passage. Clinical signs of neurological disease appeared in each steer of every group between 15 and 25 months after inoculation. An encephalopathy characterized by severe spongiform change and pronounced astrocytosis occurred in the three groups inoculated with the TME agent. In contrast, the neurohistological changes in the steers inoculated with the cattle-passaged scrapie agent were slight and subtle. Analysis of the octapeptide repeat region of the bovine protease-resistant protein (PrP) gene showed that variations in incubation period, clinical signs, and neurohistological changes were unrelated to the homozygous or heterozygous condition of six or six/five octapeptide repeats.