Immunoprophylaxis with BCG of experimental Echinococcus multilocularis infections

Previous studies have demonstrated that prophylactic treatment with BCG protects cotton rats (Sigmodon hispidus) against experimental infections with Echinococcus multilocularis; this treatment can, however, induce granulomatous reactions. In an attempt to identify a minimum prophylactic dose of BCG which would not induce granulomas, cotton rats were treated intraperitoneally with various doses of BCG (10(1) to 10(7) colony-forming units [CFU]) and then inoculated intraperitoneally with one brood capsule of the parasite. Consistent and complete protection was obtained by the inoculation of as few as 10(3) CFU of BCG. A dose of 10(1) CFU gave no protection whatsoever, and 10(2) CFU gave only partial protection. Doses larger than 10(3) (10(5), 10(7) CFU) also afforded complete protection but gave rise to granulomatous lesions. At the time of the inoculation of the parasite, protection coincided with a general elevation of leukocytes, especially cells of the monocyte/macrophage series. It is proposed that these results support evidence for the macrophage being the principal potential effector cell in hydatid disease.