Light and transmission electron microscopic characteristics of a novel Hepatozoon spp. in naturally infected cotton rats (Sigmodon hispidus).

A novel species of Hepatozoon was recently reported in cotton rats (Sigmodon hispidus) collected from an area of Oklahoma where American canine hepatozoonosis is endemic. In this study, the various stages of merogony of the parasite were characterized by light and electron microscopy. Meronts occurred within parasitophorous vacuoles in hepatocytes and ranged from mononucleated spherical forms to large, mature forms in vacuoles that contained approximately 50 peripherally arranged merozoites. Developing merozoites had characteristic apicomplexan organelles, including anterior and posterior polar rings, a conoid, microtubules, rhoptries, micronemes, and a trilaminar membrane. As the meronts matured, numerous curvilinear merozoites budded from a residual body. This morphologic characterization extends our understanding of this novel Hepatozoon and adds information about the hepatozoa, apicomplexan parasites that infect numerous species.