Two reports described human cowpox outbreaks with presumptive rodent pet sources. Cowpox is a Eurasian orthopoxvirus from the family Poxviridae and is related to the smallpox virus. Rodents are the probable reservoirs for infection. Humans are infected by scratches, bites, and direct contact with rodents or with companion animal pets (particularly cats) that have hunted rodents. Humans clinically demonstrate pox lesions at points of organism entry. These reports describe recent clusters of cowpox cases in Germany and France. Infection probably originated from pet-store rats acquired from breeders in Bavaria and the Czech Republic. Infections were isolated to a single litter in the German study and a single pet store in the French study. Several rats were clinically ill with cutaneous or respiratory signs, whereas others had no clinical signs. Humans sustained a variety of cutaneous lesions, painful lymphadenopathies, and lymphangitis characteristic of poxvirus infection. Case descriptions from the German study suggested that persons who had previously received vaccinia virus vaccinations had attenuated clinical courses. Viruses were isolated from lesional tissues. Viral DNA was extracted, polymerase chain reactions were completed, and samples were sequenced. Phylogenetic trees demonstrated that samples from both outbreaks clustered with reference cowpox sequences.

COMMENTARY: Immunocompetent people infected with cowpox may demonstrate self-limiting cutaneous disease. However, those with immunosuppressive or other disease may sustain severe disseminated infections. Veterinarians must be aware of the potential risk of rodent pets as potential poxvirus reservoirs. Immunosuppressed individuals in particular should avoid owning rodent pets. Current human populations are largely susceptible to poxvirus infection because of waning vaccinia virus immunity and poxvirus outbreaks present significant public health and bioterrorism concerns.

Cowpox virus transmission from pet rats to humans, Germany. Campe H, Zimmermann P, Glos K, et al. EMERG INFECT DIS 15:777-780, 2009.

Cowpox virus transmission from pet rats to humans, France. Ninove L, Domart Y, Vervel C, et al. EMERG INFECT DIS 15:781-784, 2009.