For the first time ever, 30 cases of cowpox in humans have been linked to contact with pet rats. Four case studies of cutaneous infections in humans were reported in early 2009, and a paper just published reports the finding that the virus was transmitted from domestic rats to humans. Wild rats, however, are the main reservoir of cowpox. While cowpox is endemic in Western Europe, and humans periodically acquire the infection through contact with either wild rats or domestic cats, this paper provides the first evidence for a link between pet rats and the spread of cowpox.
The article in ScienceDaily (http://www.sciencedaily.com/releases/2009/05/090507192933.htm) notes that these cases demonstrate the risks of zoonoses, as well as the effect of changing human behaviors in the emergence of infectious disease outbreaks. In this case, human adoption of a new pet facilitated the conditions for disease transmission.
The infections were found in 30 Europeans, 20 of whom were French. The four case studies presented with black lesions on their skin and were originally diagnosed with rickettsia. However, after samples tested negative for rickettsia, virologists used electron microscopy to confirm suspicions that these were cases of cowpox. Molecular analysis showed that the four cases were caused by the same strain of cowpox.
According to the article, the incubation period of cowpox is 1 week, and the lesions usually heal within 6 weeks. The virus is only seriously dangerous to immuno-compromised people, in whom the it can quickly spread.
The CDC's EID report can be found at http://www.cdc.gov/eid/content/15/5/pdfs/09-0235.pdf.