The use of pathophysiological reactions to assess the efficacy of the immune response to Babesia bovis in cattle.

A group of five splenectomised calves was immunised with a soluble extract prepared from erythrocytes infected with Babesia bovis and then challenged by the intravenous inoculation of virulent B. bovis along with appropriate control animals. All controls died but four of the five immunised animals survived. All survivors showed significantly lower activation of the coagulation and kinin systems and did not develop the hypotensive shock syndrome characteristic of acute B. bovis infection. It was concluded that the concentrations of fibrinogen, kininogen, and bradykinin, and the production of soluble fibrin, cryofibrinogen, and high molecular weight fibrinogen complexes were useful criteria on which to assess the efficacy of the immune response.