Cowpox virus, from the genus Orthpoxvirus, is another poxvirus that causes human disease through zoonosis.
Cowpox virus has been found only in Europe and in adjacent parts of the former Soviet Union. Despite its name, the reservoir hosts of cowpox virus are rodents, from which it can occasionally spread to cats, cows, humans, and zoo animals, including large cats and elephants. Transmission to humans has traditionally occurred via contact with the infected teats of milking cows. However, currently, infection is seen more commonly among domestic cats, from which it can be transmitted to humans.
Incubation period is generally 9 to 10 days.
Symptomatology and Outcome
Infection with cowpox virus in humans produces localized, pustular lesions at the site of their introduction into the skin. The lesion is similar to that caused by vaccination, although the inflammatory response is greater. The lesions in humans usually appear on the hands: on the thumbs, the first interdigital cleft, and the forefinger. Fever and myalgia may be present in some cases, but this is rare. Secondary lesions occur only in individuals with immunological deficiencies.
Pathology and Pathogenesis
The pathology of the skin lesions caused by cowpox virus is similar to that of smallpox. However, there is greater epithelial thickening and less rapid cell necrosis. There is also more involvement of the mesodermal tissues. The most significant pathological feature of cowpox is the presence of two types of cytoplasmic inclusion bodies: irregular B-type inclusion bodies, and numerous large, homogenous, acidophilic, A-type inclusion bodies.
Management and Prevention
Human cowpox usually responds to treatment with antivaccina immunoglobulin. However, this should be restricted to the most severe cases. Usually, the lesions regress spontaneously.
Identification and isolation of animals infected with cowpox can help decrease the incidence of human infections. Attention to the newly emerging prevalence of cowpox virus among domestic cats and subsequent, directive action can also help reduce the number of human infections. Proper hand washing, as with most viruses, is also recommended.