To obtain more information about the interferon gamma test used for diagnosis of paratuberculosis in goats, three categories of herds were tested: non-vaccinated herds without paratuberculosis; herds that had been vaccinated against paratuberculosis but had never shown clinical signs of paratuberculosis nor given positive M. a. paratuberculosis fecal samples and herds that had a history of paratuberculosis, had given positive M. a. paratuberculosis fecal samples and were vaccinated. Heparinized blood was stimulated with purified protein derivate (PPD) from M. a. paratuberculosis for 24 h and plasma was assayed for the presence of interferon gamma. Results were recorded as the difference between OD values of PPD stimulated and control samples. Due to geographical matters, blood samples were set up in the gamma interferon assay the day after they were sampled. In order to test the viability of the blood samples, positive stimulations with SED were set up. Only 1% of the 1200 animals originating from herds free of paratuberculosis gave weak positive responses in the interferon gamma test (delta OD exceeding 0.2). However, about 5% of the animals had positive responses in control samples and had to be re-sampled.Vaccinated animals from herds with paratuberculosis showed significant higher responses than animals from vaccinated herds without paratuberculosis. Some of the vaccinated animals had a response lasting for several years, which demonstrate a long lasting interference with diagnostic testing. In both these groups responses were correlated to age with higher responses in younger animals.Although more information about the early interferon gamma responses of naturally infected goats and the presence of false negative tests in infected animals is needed, we conclude that the low responses of non-infected animals indicate that this test may be useful in monitoring the paratuberculosis status in non-vaccinated goat herds.

Sponsorship

Attendance to this conference was sponsored by the EU-funded co-ordination action SSPE-CT-2004-501903