Ewe-lamb transmission of ovine Johne's Disease.

Abstract

Knowledge of the likelihood of intrauterine or transmammary transmission of M. a. paratuberculosis infection in sheep is important in the design of control programs. Little has been published on this aspect of ovine Johne's disease, although studies in cattle have found up to 25% of foetuses from clinically affected cows to be infected. In this study 151 ewes from heavily infected flocks and their late term foetuses were examined using all available antemortem and necropsy tests. Five of six ewes with clinical OJD had infected foetuses. One of 54 subclinically affected ewes and none of 16 apparently uninfected ewes had infected foetuses. Only two ewes (both clinical cases which also had infected foetuses) had detectable M. a. paratuberculosis in their milk or mammary glands. Thus, although intrauterine or transmammary transmission may occur frequently in clinically affected sheep, it is infrequent in subclinically infected ewes or in ewes not detectably infected (even if from a heavily infected flock), suggesting that this mode of transmission is unlikely to significantly affect existing OJD control programs.