Dogs and opossums positive for vaccinia virus during outbreak affecting cattle and humans

During a vaccinia virus (VACV) outbreak in São Paulo State, Brazil, blood samples were collected from cows, humans, other domestic animals, and wild mammals. Samples from 3 dogs and 3 opossums were positive for VACV by PCR. Results of gene sequencing yielded major questions regarding other mammalian species acting as reservoirs of VACV.

Since the first vaccinia virus (VACV) outbreak in Brazil in 1999, researchers have speculated on the origins and possible reservoirs of VACV. Wild and peridomestic rodents are known to be reservoirs of cowpox in Europe, but in Brazil, their involvement as VACV reservoirs is unclear. Although studies have reported experimental transmission of VACV between rodents and cows, this finding was not confirmed during outbreaks in Brazil.

The isolation and characterization of a VACV isolate in a peridomestic rodent has been described on a farm in Minas Gerais State, which raised questions about the role of rodents in VACV maintenance in Brazil. However, a recent serologic study on VACV reservoirs suggested that wild rodents might have a secondary role in VACV maintenance in São Paulo State.

Despite the absence of reports of clinical signs in dogs and other domestic or wild mammals during VACV outbreaks, in this report, we describe 3 dogs (Canis lupus familiaris) and 3 opossums (Didelphis albiventris) without clinical signs that were obtained during from a VACV outbreak. Blood samples from these animals were positive by PCR for VACV.  Emerging Infectious Diseases  Original web page at Emerging Infectious Diseases