Chronic splenitis as a possible complicating factor in calves inoculated with an attenuated redwater vaccine

In two consecutive years a total of 3810 calves were inoculated with the Onderstepoort redwater live-blood vaccine, containing attenuated strains of Babesia bigemina and Babesia bovis. Twenty calves died 8-13 days later due to B. bigemina-infection. Necropsies were performed on 19 of these animals. In 11 calves the spleen was distinctly smaller than normal and its morphology was distorted, and showed changes of chronic splenitis. Histological lesions in the spleens of 6 of the 11 calves are described. The potentiating effect of the splenic lesions to reduce the ability to contain the vaccine reaction, is discussed.