Crystalline inclusions in erythrocytes parasitized with Babesia equi following treatment of ponies with imidocarb.

Four splenectomized Welsh ponies were infected with Babesia equi. Two ponies were treated with imidocarb dipropionate, and two were not treated. By light microscopic examination, 1% to 2% of the parasitized erythrocytes of treated ponies contained crystalline inclusions. The crystals were rectangular, diamond, or burr shaped. They occupied most of the erythrocytic cytoplasm, and, as a result, the remainder of the pale staining cytoplasm was inconspicuous in Wright-Giemsa-stained blood smears. The size and shape of intraerythrocytic inclusions varied when examined by electron microscopy, but in most instances they were either adhered to or were located close to the parasite. The sides of crystals were either smooth or serrated, and corners were either sharp or notched. Fractures or faults were common in large crystals. Parasitized erythrocytes of nontreated ponies and nonparasitized erythrocytes of treated ponies did not contain crystals. Four hemoglobulin types were identified in five noninfected, nontreated Welsh ponies from the same herd.