Ultrastructural characteristics of Babesia caballi in equine erythrocytes in vitro

Babesia caballi cultured continuously in equine erythrocytes was examined b y transmission electron microscopy. The use of cultured B. caballi permitte d examination of a large number of parasitized cells with various stages of intra erythrocytic development. The piriform merozoites of B. caballi were composed of an outer membrane and an inner double-membrane complex. Numero us micronemes and three rhoptries were found in the pellicle of the merozoi te, and a spherical body was seen in the anterior part of the merozoite whi ch usually lay adjacent to the nucleus and the pellicle. These findings wer e similar to those for merozoites of bovine Babesia parasites such as B. bi gemina. The trophozoites were surrounded by a single membrane, were continu ously changing their body shape with extension and retraction of the pseudo pod. A long pseudopod extended far into the host cell cytoplasm, and was fi nally completely enclosed in a cell, but did not have hemozoin pigment, the breakdown product of hemoglobin digestion.