This progressive neurologic disease of mink is rare, but mortality may reach 60%–90% of the ranch population. The incubation period is 8–12 mo. Mink usually bite compulsively, are incoordinated and somnolent, scatter feces in the pen, and flip their tails up over their backs (like squirrels). Histologic lesions of the brain are spongiform changes of the gray matter, astrocytosis, and neuronal vacuolation. The demonstration of disease-specific prion protein in nervous tissues aids in the diagnosis. Although the means of transmission is unknown, “downer” cattle are suspected to be the source of the agent. There are no vaccines or treatment.