Development of Babesia gibsoni in the midgut of larval tick, Rhipicephalus sanguineus

Studies were made on the development of Babesia gibsoni in the midgut of the larval tick, Rhipicephalus sanguineus. Six hr after repletion, merozoites of B. gibsoni, freed from erythrocytes, were observed in the midgut contents of the tick. After that, within 24 hr, those merozoites were transformed into the ring-forms which were relatively large, 2-3 μm in diameter. Later, the ring forms developed into the spherical forms which were subelliptical in shape and 4-6 μm in diameter. Within 2-4 days, the elongated forms, 5-8 μm in length, were found. At this time, some of the binucleated fusion form has assumed a form intermediate between the spherical and elongated-forms. About 5-6 days after repletion, large round or elliptic zygotes, 8-10 μm in diameter, were observed in the tick gut.