Course of infection by Babesia sp. BQ1 (Lintan) and B. divergens in sheep depends on the production of IFNgamma and IL10.

Ovine babesiosis is an important disease in China and responsible for economic losses. Several Babesia strains are involved, but Babesia sp. BQ1 (Lintan) and Babesia sp. BQ1 (Ningxian) are particularly prevalent in the Guansu region. Babesia divergens, in contrast, can experimentally infect spleen-intact sheep, but does not induce clinical signs. The immune response of spleen-intact sheep to Babesia sp. BQ1 (Lintan) and to B. divergens was therefore compared to identify the immune mechanisms involved in pathogenicity. The greater pathogenicity of Babesia sp. BQ1 (Lintan) than that of B. divergens was confirmed: sheep infected with Babesia sp. BQ1 (Lintan), but not with B. divergens, developed hyperthermia and showed patent parasitaemia in Giemsa-stained blood smears from the ear vein. Furthermore, more parasites were also detected in the blood from the jugular vein of Babesia sp. BQ1 (Lintan)-infected sheep. Pathogenicity of Babesia spp. involved cellular responses, but not humoral responses. Interferon-gamma was produced only by specifically activated PBMC from B. divergens-infected sheep and interleukin-10 only by specifically activated PBMC from Babesia sp. BQ1 (Lintan)-infected sheep. The role of these cytokines in the course of infection by Babesia spp. is discussed.