IMMUNIZATION OF SHEEP AGAINST HEARTWATER WITH INACTIVATED COWDRIA-RUMINANTIUM

The immunisation of sheep with inactivated Cowdria ruminantium organis ms (the causative agent of heartwater) emulsified in Freund's adjuvant induced protective immunity against a homologous challenge with virul ent cell culture-derived C ruminantium organisms. This protective immu nity was associated with the development of high titres of C ruminanti um-specific antibodies, a low level of rickettsiosis in brain endothel ium and no mortalities. In contrast, when unimmunised sheep were chall enged, they developed higher levels of rickettsiosis in brain endothel ium, and some of them died. This method of immunisation against heart- water has the potential to replace the infection and treatment method that is in current use.