Transmissible congenital demyelinating encephalopathy of lambs.

Twenty-two fetal lambs were inoculated in utero with tissue suspension prepared from lambs born with weakness, incoordination and clonic tremor. Clinically, affected newborn lambs had clonic tremor, were generally weak and had abnormally pigmented hairy fleece. The inoculation resulted in a disseminated encephalomyelitis with secondary teratologic changes in a significant number of fetuses. The mononuclear inflammatory changes were most obvious 14 days after inoculation, after which there was rapid resolution. Changes seen at birth were chronic astrocytosis with neuron loss in the spinal cord and cerebellar dysplasia. Single radioimmunodiffusion studies showed consistently low IgG in infected fetuses and high IgG in lambs at birth.