Mechanism of Immunity in Hæmorrhagic Septicæmia

Abstract

HÆMORRHAGIC septicæmia of cattle and buffaloes caused by Pasteurella multocida type I kills many thousands of animals in Asia each year. It is possible to immunize against the disease effectively with improved vaccines, and in addition 5–10 per cent of animals possess a naturally acquired immunity. Both kinds of immune animals have in their sera circulating antibodies which are detectable by the passive mouse protection test. Hitherto, it has been difficult to find whether these protective antibodies operated by a bactericidal or an opsonizing mechanism. Experiments using cultured bacteria, even those from primary plates sown with infected blood, showed no significant differences between known positive and negative sera in the bactericidal test of Muschel and Treffers¹, or in phagocytosis tests in roller tubes using heparinized or citrated blood.