Characterisation of poxviruses from sporadic human infections.

An orthopoxvirus was isolated from the vesicular rash of a man in Natal who died in coma and who had not been vaccinated. Analysis of the viral DNA showed that it was a vaccinia virus, more closely related to the virus of South African smallpox vaccine than to other vaccinia viruses. DNA analysis also showed that an orthopoxvirus isolated from a sporadic case of severe pustular rash in Nigeria was a vaccinia virus closely related to the smallpox vaccine virus used there. Minor biological differences between the viruses isolated and the corresponding vaccine strains suggested that some natural transmission of the virus had occurred, but the results of DNA analysis implied that they originated from the use of smallpox vaccine. No similar cases have been detected since smallpox vaccination was discontinued.