Ultrastructural Observations on Renal Schizogony of Leucocytozoon dubreuili in the American Robin

Abstract

The schizogonic development of L. dubreuili in the kidney proximal tubule cells of the American robin, Turdus migratorius, was studied by EM. Renal schizogony is initiated by the entry of certain hepatic merozoites into cells of the proximal tubules. Development of the schizont consists of a coordinated sequence of events including extensive mitotic nuclear division, multiplication of mitochondria, increase in endoplasmic reticulum and ribosomes, differentiation of membranes, microtubules, micronemes and rhoptries, and cytoplasmic segmentation (cytomere formation). Merzoites form by budding around numerous centers in the schizont and, when mature, are bounded by a single plasma membrane subtended by microtubules. Each merozoite contains a large nucleus, a mitochondrion and a well developed apical complex consisting of 3 polar rings, paired rhoptries and numerous micronemes. An atypical nuclear division observed in some maturing schizonts was characterized by the multiple fission of a nucleus within a persistent outer nuclear membrane and the absence of mitotic spindle apparatus. Alterations in infected renal cells consisted of disorganization and loss of cytoplasmic organelles and the accumulation of lipofuscin-like inclusions.