My current research investigates the interaction between the Maedi-Visna virus of sheep and Mycobacterium avium subs. paratuberculosis. Both of these diseases have a major impact on sheep and goat production, and both modulate host immune responses. These pathogens are widespread within Ontario sheep and goat herds, so many animals likely harbour more than one infection. The impact however, of co-infection on host immunity, health, and production remains unknown.