POXVIRUS INFECTION IN DOMESTIC CATS - CLINICAL, PATHOHISTOLOGICAL, VIROLOGICAL AND EPIZOOTIOLOGICAL STUDIES

In the present paper two cases of poxvirus infection in domestic cats are reported: first, a 10-week-old male cat showed a localized ulcerated lesion on the left forearm, about 1.5 cm in diameter; five days later the patient was found to have developed multiple smaller lesions all over the body. A tentative diagnosis was based on a scraping of a lesion, in which eosinophilic intracytoplasmic inclusion bodies could be observed in epithelial cells. The diagnosis was confirmed by means of a skin biopsy. Ultrathin sections prepared for electron microscopy contained virions of poxvirus morphology. Another biopsy of one of the skin lesions was homogenized and the supernatant was inoculated onto a monolayer of Vero cells: cytopathic effect was first noticed 24 to 36 hours after inoculation, consisting of plaque formation, syncytia and giant cells. HE-stained preparations showed the inclusion bodies mentioned above. These inclusions stained green with acridine-orange, indicative of a double-stranded nucleic acid. Following high-speed centrifugation of the cell culture supernatant orthopoxvirus particles could be demonstrated using negative staining and electron microscopy. The course of the disease was mild, the lesions resolved over a period of 5 weeks and the cat recovered. The convalescent serum contained high-titred orthopoxvirus antibodies, as evidenced by haemagglutination-inhibition (HI) and virus-neutralisation (VN) tests. Recently a second case of poxvirus infection was demonstrated in a 10-year-old female cat. The animal had developed a single lesion of 1.5 x 1 cm at the right fore paw. The lesion was removed and diagnosis was established histologically. All persons, who came in contact with one of the diseased cats, including a 10-year-old girl, who had not been vaccinated against smallpox, remained healthy. In 200 serum samples of clinically healthy cats the prevalence of antibodies to ortho- and parapoxvirus was investigated. All samples were from animals that had been allowed to roam outside and to hunt rodents. HI antibodies to orthopoxvirus have been found in 4 % of the serum samples, with titres ranging between 16 and 512. The specificity of the results was verified by VN test. These results imply that, at least in Austria, unrecognized or subclinical orthopoxvirusinfection,in cats is more common than previously thought. On the other hand all sera proved negative to parapoxvirus in VN test. While this paper was in press we diagnosed 2 additional cases of poxvirus infections in domestic cats. investigation of biopsy specimens of skin lesions enabled the etiologic viruses to be isolated and identified as orthopoxviruses.