Encephalitis following vaccination against distemper and infectious hepatitis in the dog. An optical and ultrastructural study.

A 4-month-old, male, healthy dog developed CNS-symptoms 10 days after the second vaccination with live, attenuated distemper and canine hepatitis virus. The animal was euthanized after 2 weeks of illness. Light and electron microscopic examination of the CNS showed a partly necrotizing encephalomyelitis with numberous intranuclear and intracytoplasmic inclusion bodies, and the presence of probable pseudomyxovirus nucleocapsids and of crystalloid and tubuloreticular aggregates. Although there was conformity of inclusion bodies and probable viral structures as revealed by electron microscopy, the latter showed a much wider distribution. In addition, viral structures of a different type were found in polymorphonuclear leukocytes and vascular endothelial cells. Several morphological criteria led to the supposition that they are Picornaviruses, or possibly Arenaviruses. It is thought that their role in the disease process was at best an indirect one.