Immunisation of sheep against heartwater with inactivated Cowdria ruminantium.

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