Studies on immunity in heartwater

Abstract

1. It has been confirmed that the immunity in sheep following recovery from infection comprises a short period of premunition, followed by a period of gradually decreasing sterile immunity. 2. Infection during the period of sterile immunity again initiates the cycle premunition, sterile immunity. 3. Circulating virus is detectable in the peripheral circulation of immune sheep following reinfection, whether a demonstrable reaction is produced or not. 4. Up to a period of four years after recovery - the limit of the experiment - the residual immunity is sufficient to protect against fatal infection in sheep under laboratory conditions. 5. The significance of these findings and their relation to the problem of the control of heartwater are discussed.