In vitro cultivation of Babesia equi: detection of carrier animals and isolation of parasites.

By means of an in vitro culture technique, 75 samples of horse blood were examined for Babesia equi, a causative agent of equine piroplasmosis. At the time of culture initiation, 15 samples were microscopically positive for B. equi, and this was subsequently confirmed by culture diagnosis. Sixty samples showed no parasites in Giemsa-stained thin blood smears. However, after the culturing process, parasites were found in blood smears of 36 of these samples. The sensitivity of the in vitro culture method was such that 2.5 microliters (1/40 of the usual volume used for the above-mentioned samples) of packed erythrocytes obtained from a carrier horse still yielded positive results after cultivation. Cultures were initiated from blood samples stored for up to 120 h at 8 degrees C in vacuum tubes containing EDTA as anticoagulant. These results show that the in vitro culture method is highly sensitive. It can be used to identify B. equi carrier horses, to evaluate the effects of chemotherapeutic intervention, and to isolate field strains of B. equi for further characterization.