Latent Infection of Canine Herpes Virus in Laboratory Beagle Dogs

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The latent infection of canine herpes virus was investigated in laboratory beagles with no clinical abnormalities. In eight of twenty-three male dogs which were purchased from the same breeder at the age of six months, the pathogen was confirmed at the age of one year by immunological, histopathological or electron-microscopical examinations. The infected beagles seemed to be healthy in several clinical examinations including blood- and serum-biochemical analyses. The neutralizing titer of the canine herpes virus antibody test ranged from 64 to 128, compared to the undetectable titer in animals obtained from a different breeder and housed in the same conditions. Histopathological examinations revealed eosinophilic inclusion bodies in the cytoplasm of swollen or damaged epithelium of renal papillary ducts, papilla, and/or pelvis accompanied by chronic pelvic inflammation. The inclusion bodies showed positive reaction against anti-human herpes simplex virus antigen. Electronmicroscopically, these inclusion bodies consisted of numerous intracytoplasmic aggregates of virion. The virion particles were round to hexagonal, the envelope or capsid about 140 nm in diameter and arranged in a fine crystalline array. This evidence strongly suggests that the virions were excreted from the body by urination. Although these animals were housed in our laboratory for about half a year, the other beagles housed in separate cages in the same room were not infected by the virus. The results show the importance of preventative measures against latent canine herpes virus infection and maintenance of laboratory conditions to avoid this problem.