Pathology and epidemiology of canine distemper in raccoon dogs (Nyctereutes procyonoides).

From September to December 1991, a large number of free-ranging raccoon dogs (Nyctereutes procyonoides) died from a highly contagious disease in the vicinity of Tokyo. Eighteen seriously ill or dead animals were submitted for necropsy. The pathological findings resembled those in a masked palm civet (Paguma larvata) found infected with canine distemper virus (CDV) in the same area in late August 1991. The most striking features were pneumonia and gastroenteritis. Microscopical lesions consisted of cytoplasmic and intranuclear eosinophilic inclusion bodies in various organs and tissues, bronchiolointerstitial pneumonia, non-suppurative demyelinating encephalitis, lymphocytic depletion in various lymphoid tissues and catarrhal or necrotizing gastroenteritis. CDV-specific antigens, demonstrated immunohistochemically in the epithelial tissues, central nervous system and lymphoid tissues, corresponded with the presence of the eosinophilic inclusion bodies in sections of the same lesions stained with haematoxylin and eosin. Ultrastructurally, both cytoplasmic and intranuclear inclusion bodies were observed to be composed of aggregates of viral nucleocapsids. The study provided clear evidence that CDV was the cause of the disease. It is possible that the masked palm civet introduced the infection into the raccoon dog population.