Ultrastructural observations on the developmental stages of Lankesterella minima (Apicomplexa) in experimentally infected Rana catesbeiana tadpoles.

During May to August 1988, the prevalence of Lankesterella minima in bullfrog tadpoles and adults in the vicinity of Lake Sasajewun, Algonquin Park, Ontario, was 54.8% and 29.4%, respectively. The parasite was transmitted to laboratory-reared tadpoles through the bite of experimentally infected, laboratory-reared leeches (Batracobdella picta). Intraerythrocytic sporozoites were observed in the experimentally infected tadpoles 36 days postexposure (PE) to leech bites. Sporogonic stages in these tadpoles were examined by light and electron microscopy. Oocysts developed in vascular endothelial cells of several organs. Multinucleate oocysts at 29 days PE lay in a parasitophorous vacuole and contained several large inclusions. Mature oocysts, observed 32 days PE, contained about 70 sporozoites that exhibited typical apicomplexan features. In the posterior region of the sporozoites, 12 helically arranged chains of electron-lucent intrapellicular extended anteriorly from a dense terminal ring.