Development of Gametocytes and Second Asexual Generation Stages of Eimeria auburnensis in Calves

Abstract

Thirty calves were used to study the endogenous stages of Eimeria auburnensis, and 6 additional calves were employed to investigate the patent and prepatent periods. Second-generation schizonts and gametocytes occurred in a subepithelial location in cells of mesodermal origin in the distal portion of the villi. Trophozoites and immature schizonts of the second generation were found in calves killed 10 and 12 days after inoculation. Mature second-generation schizonts, observed in 12-, 14-, and 15-day infections, had 4 to 11 merozoites. A number of host cells harbored gametocytes in addition to the mature second-generation schizonts. Gametocytes were first seen on the 14th day after inoculation. Macrogametes had large nuclei and nucleoli, and many had a basophilic body near the nucleolus. Cytoplasmic granules first appeared at 16 days after inoculation; the oocyst wall began to form at 17 days after inoculation, and at 18 and 19 days many fully formed oocysts were seen. Only the youngest macrogametes, seen at 14 days after inoculation, were Feulgen-positive; all others were Feulgen-negative. PAS-positive granules were seen in increasing numbers in macrogametes beginning on the 15th day after inoculation. In oocysts the entire cytoplasm appeared strongly PAS-positive. Microgametocytes were first distinguishable in 14-day infections. During early development the nuclei were randomly arranged, but in more advanced microgametocytes, the nuclei were arranged at the periphery of internal compartments, whose interior had lightly stained residual material. Microgametes formed in rows at the surface of the compartments; later they were arranged in whorls. Mature microgametocytes were seen in abundance in 18and 19-day infections. Microgametocytes were PAS-positive in areas corresponding to the location of microgametes. Basophilic crescent-shaped bodies were observed in the parasitophorous vacuoles of host cells parasitized by macrogametes and microgametocytes. These were PAS-negative and Feulgen-negative; their significance is unknown. In 6 calves, the mean prepatent period for E. auburnensis was 17.5 days and the patent period averaged 3.3 days. The sexual stages of Eimeria auburnensis have been briefly described (Hammond, Clark, and Miner, 1961; Davis and Bowman, 1962). Recently an account of the development of the first-generation schizonts of this species was given (Chobotar, Hammond, and Miner, 1969). In the present paper we report the occurrence of a previously undescribed second generation of schizonts and present additional information concerning the development of the