HETEROLOGOUS STRAIN CHALLENGE OF CATTLE IMMUNIZED WITH ANAPLASMA-MARGINALE OUTER MEMBRANES

In this study, we tested the hypothesis that outer membrane immunizati on would induce protection against an antigenically variant strain. Ou ter membranes were isolated from the Virginia strain of Anaplasma marg inale using density gradient centrifugation, combined with saponin adj uvant, and used to immunize Friesian cattle in Zimbabwe. Immunized cat tle developed high antibody titers (80 000-160 000) against outer memb rane polypeptides including MSP-2 and MSP-5 in both the homologous Vir ginia and heterologous Zimbabwe strains. Outer membrane immunized catt le were protected significantly following challenge with 10(4) Zimbabw e strain parasitized erythrocytes, demonstrated by significant differe nces in prepatent period and peak rickettsemia compared with adjuvant immunized control cattle. One outer membrane immunized animal was comp letely protected against infection. However, there were no overall sig nificant differences in severity of anemia between cattle immunized wi th outer membrane and the control group, indicating that a significant reduction in rickettsemia does not necessarily result in less severe anemia.