Cowpox virus in a 12-year-old boy: rapid identification by an orthopoxvirus-specific polymerase chain reaction.

Although smallpox was eradicated 20 years ago, other members of the genus Orthopoxvirus (OPV), such as cowpox virus (CPXV) or monkeypox virus, are still a threat to humans. Because human CPXV infection is rare, it is seldom suspected on clinical grounds only. We report a boy who presented with two necrotic ulcers with surrounding erythema. Infection with OPV was suspected, as antibiotic treatment had not produced improvement and smears were negative for anthrax. An OPV was isolated and an OPV-specific polymerase chain reaction combined with a subsequent restriction enzyme fragment length polymorphism assay confirmed infection by CPXV. Although the patient's cat had had no skin lesions, OPV-specific antibodies were found at a titre of 1 : 8 in a plaque reduction assay, suggesting that the cat had transmitted the virus to the boy.