Poxvirus Infection in Zoo-Kept Mammals

Abstract

Between 1960 and 1986 at least 22 outbreaks of pox disease have been observed in elephants (Elephas maximus, Loxodonta africana), rhinoceroses (Ceratotherium simum, Diceros bicornis), okapis (Okapia johnstoni) and other mammals (family Felidae, ordo Edentata) in European zoological gardens. 21 outbreaks lie within a circle with a diameter of 1070 km around a taken center near Magdeburg. Only the Moscow outbreak occurred outside of this circle. Since in some zoological gardens children are allowed to ride on elephants, it had been assumed that the virus had been introduced into the zoo by persons recently vaccinated against smallpox. In 10 cases orthopoxvirus strains were isolated which were similar but not identical in their biological properties. But in contrast to vaccinia virus these virus strains produce small (1 – 2 mm in diameter) lesions with a haemorrhagic center on the chorioallantoic membrane, intracytoplasmic inclusions of type A V +, and characteristic skin lesions in laboratory mice. Since they resemble cowpox virus they were called cowpoxlike virus strains. The coincidental occurrence of some outbreaks and the restriction to a limited region within Europe support the hypothesis that zoo-kept mammals are only indicators of a certain hidden virus cycle. DNA analysis with restriction enzymes revealed a certain heterogeneity of the genome outside the conservative region characteristic for the orthopoxvirus genus. Recent virus isolations from a cat and humans living in close contact with domestic cats in the Netherlands and Germany revealed a close relatedness between these strains and the cowpoxlike virus strains isolated from zoo-kept mammals. These findings support the hypothesis that a small wild-living mammal may be the primary reservoir for cowpox or cowpoxlike viruses.