Pilot study : tracer weaner trial for ovine Johne's Disease : National Ovine Johne’s Disease Control and Evaluation Program.

Abstract

Eradication of ovine Johne’s disease requires destocking sheep and spelling land until Mycobacterium avium subsp. paratuberculoisis has died out. There is no simple way to assess the residual level of contamination or the risk this poses to livestock. Consequently small groups of Merino weaners were orally dosed with M. avium subsp. paratuberculosis. Within 7-14 weeks the organism could be cultured from various locations in the gastrointestinal tract and associated lymph nodes. In addition, the results of a skin test were positive in 66% of weaners in which the organism had established an infection and were negative in uninfected sheep. The results of tests for gamma interferon were positive in some infected weaners but also in some of the controls. An ELISA test was not useful at this early stage of infection. Overall, the results suggest that weaner sheep could be used as sentinels in an infected environment, but this requires validation in a controlled field trial. Furthermore, the results suggest that the infectious dose of M. avium subsp. paratuberculosis may be higher than previously thought.