Detection of enzootic babesiosis in baboons (Papio cynocephalus) and phylogenetic evidence supporting synonymy of the genera Entopolypoides and Babesia

Blood smear evaluation of two baboons (Papio cynocephalus) experiencing acu te hemolytic crises following experimental stem cell transplantation reveal ed numerous intraerythrocytic organisms typical of the genus Babesia. Both animals had received whole-blood transfusions from ho baboon donors, one of which was subsequently found to display rare trophozoites of Entopolypoide s macaci. An investigation was then undertaken to determine the prevalence of hematozoa in baboons held in our primate colony and to determine the rel ationship, if any, between the involved species. Analysis of thick and thin blood films from 65 healthy baboons (23 originating from our breeding faci lity, 26 originating from an out-of-state breeding facility, and 16 imparte d from,Africa) for hematozoa revealed Fare E. macaci parasites in 31%, with respective prevalences of 39, 35, and 12%. Phylogenetic anal, sis of nucle ar small-subunit rRNA gene sequences amplified from peripheral blood of a b aboon chronically infected with E, macaci demonstrated this parasite to he most closely related to Babesia microti (97.9% sequence similarity); sera f rom infected animals did not react in indirect fluorescent-antibody tests w ith Babesia microti antigen, however, suggesting that they represent differ ent species. These results support an emerging view that the genus Entopoly poides Mayer 1933 is synonymous with that of the genus Babesia Starcovici 1 893 and that the morphological variation noted among intracellular forms is a function of alteration in host immune status. The presence of an underre cognized, but highly enzootic, Babesia sp, in baboons may result in substan tial, unanticipated impact on research programs. The similarity of this par asite to the known human pathogen B. microti may also pose risks to humans undergoing xenotransplantation, mandating effective screening of donor anim als.