Viremia in human Cowpox virus infection

Several poxviruses can infect humans and cause diseases of varying severity. Besides the eradicated Variola virus that induced high mortality rates, numerous further human pathogenic orthopoxviruses are potentially fatal but generally cause less severe infections. While infection-related viremia was described for Variola virus and seems to be rare for Monkeypox virus, it is still debated for Vaccinia virus. So far, viremia in Cowpox virus-infected humans has not been reported.

To estimate the potential risk of Cowpox virus to disseminate and develop severe infections, two Cowpox virus patients were examined for viremia.

Whole blood, serum and fluid from virus-induced lesions were analyzed by serology or quantitative real-time PCR.

Real-time PCR and sequence analysis of the hemagglutinin gene confirmed Cowpox virus in the lesions of both patients. Serology performed on serum obtained at the same time as the lesion specimens demonstrated orthopoxvirus-specific IgG and IgM antibodies, indicating a recent orthopoxvirus infection. In addition, Cowpox virus DNA was detectable in whole blood, but not in serum, as late as week 4 post-infection.

In contrast to observations following vaccination with Vaccinia virus, DNAemia in patients with localized symptoms of a Cowpox virus infection does not seem to be a rare event. However, its relevance for Cowpox virus pathogenicity has to be elucidated.