Introduction.

Paratuberculosis is common among goats in Norway, and the disease is controlled by vaccination. There is some concern that cheese manufactured from raw goats' milk might lead to transmission of M. paratuberculosis to humans. The aims of the present study were to determine if M. paratuberculosis could be detected in goats' milk in Norway and to elucidate the possible role of a live vaccine for the presence in milk.

Material and methods.

Milk samples from 340 goats were examined for M. paratuberculosis by culture and immunomagnetic separation combined with IS900 PCR (IMS-PCR). PCR products from positive samples were sequenced, and BLAST queries against public databases were performed.

Results.

Viable M. paratuberculosis were not detected by culture in any of the 340 milk samples, but 24 samples tested positive by IMS-PCR. The percentage of IMS-PCR positive milk samples from herds where paratuberculosis had previously been reported was lower (3,3%) than from herds where the infection had never been diagnosed (9.5%). Herds with a known paratuberculosis problem might have a herd management that prevent spread of the infection, while the infection is free to spread in herds with an unknown paratuberculosis status. Vaccination of goats with a live paratuberculosis vaccine did not seem to interfere with shedding in milk, since M. paratuberculosis was detected in almost the same percentage of milk samples from vaccinated and unvaccinated goats. There were a significantly higher proportion of positive samples among those collected in May (13,8%) than among those collected during February to April (2,9%). PCR products from five milk samples showed homologies of 97 to 100% with the IS900 sequence from M. paratuberculosis. This is important as IS900-like elements detected by PCR have been found in mycobacteria other than M. paratuberculosis, so detection by IS900 PCR alone might lead to false positive results.