Detection and quantification of parapoxvirus DNA by use of a quantitative real-time polymerase chain reaction assay in calves without clinical signs of parapoxvirus infection.

OBJECTIVE: To investigate the presence of parapoxvirus (PPV) in cattle without clinical signs of infection and in farm environments of PPV-infected cattle. ANIMALS: 28 calves without clinical signs of PPV infection on 2 farms and 11 clinically affected calves on 6 farms. PROCEDURES: 164 oral swab samples were collected at regular intervals from 28 calves without clinical signs of PPV infection, and 11 swab samples were collected from 11 clinically affected calves. Viral DNA load was quantified by use of a PPV-specific quantitative real-time PCR (qRT-PCR) assay. RESULTS Of 28 calves without clinical signs of PPV infection, 12 had positive results for PPV DNA by use of the qRT-PCR assay. Viral DNA was detected continuously over a period of 2 to 5 months from 9 of these 12 calves, particularly from calves with dermatomycosis or respiratory tract disease. The PPV DNA loads in 32 oral swab samples from these 12 calves were significantly lower (median, 3.2 copies/mg) than those in samples collected from the 11 clinically affected calves (median, 3.2 × 10(4) copies/mg). Moreover, PPV DNA was detected in the residual feed and drinking water on both farms that housed the calves without clinical signs of PPV infection. CONCLUSIONS AND CLINICAL RELEVANCE: PPV in cattle without clinical signs of infection and in the environments of these cattle may represent sources of PPV transmission to susceptible cattle. IMPACT FOR HUMAN MEDICINE: Humans should wear gloves to prevent zoonotic disease transmission when handling cattle with or without clinical signs of PPV infection.