Schizogonous Stages of Eimeria acervulina Tyzzer, 1929

Abstract

TYZZER¹ found no endogenous stages in the life cycle of Eimeria acervulina in the chicken until the third day after infection when schizonts appeared in the epithelial cells of the duodenal villi, and sexual stages appeared on the fourth day. Moyihan² observed developing forms in the epithelial cells of the crypts of Lieberkühn of the duodenum, but did not specify the stage or the time after infection. Recently, sporozoites have been shown in the glands of Lieberkühn one day after infection^3–6. Doran⁶ gives a detailed description of the migration of the sporozoites, which develop into the first generation schizonts in the glandular epithelium by the second day after infection^4–8. The mean dimensions of the first generation schizonts, which lie above the host cell nucleus, were 4 × 6µ; each one contained four to twelve merozoites⁵. These figures are subject to staining distortion. This newly observed stage in the life cycle of E. acervulina raises the question of whether one or two asexual stages occur after this stage and before the sexual generation, particularly because no morphological differences have so far been observed between any later schizonts developing at different times in the epithelial cells of the villi. Sections of the upper intestines of birds taken 3 days after infection show mature schizonts in the glands and in the crypts of Lieberkühn as well as developing merozoites in the epithelial cells of the villi; on the fourth day after infection there are mature schizonts and immature gametocytes, and on the fifth day gametocytes, oocysts and schizonts are present, which suggests the possibility of a total of three schizogonous stages before the commencement of gametogony and one stage concurrent with the sexual phase.