Protection of mice against haemoprotozoan Babesia microti with Brucella abortus strain 19.

When Brucella abortus strain 19 is given intraperitoneally to mice it protects them against subsequent infection with large doses of Babesia microti. The protection obtained was more effective when B. abortus was given intraperitoneally than when it was injected subcutaneously. This non-specific protection seems to be best explained by the stimulation of macrophages so as to release a mediator which limits the intracellular replication of the parasites.