The life history, ultrastructure, and experimental transmission of Hepatozoon catesbianae n. comb., an apicomplexan parasite of the bullfrog, Rana catesbeiana and the mosquito, Culex territans in Algonquin Park, Ontario.

Gametogenesis and sporogonic development of a haemogregarine parasite of bullfrogs (Rana catesbeiana) was observed in cells of the Malpighian tubules of laboratory-reared Culex territans that had fed on naturally infected bullfrogs. Mature oocysts, which varied considerably in size, were multisporocystic with ellipsoidal sporocysts that contained 4 sporozoites. Sporogonic development was completed in about 20 days. Mature meronts were observed in the liver and merozoites in erythrocytes of laboratory-reared bullfrogs that had been fed sporocysts 19 days previously. Similar attempts to infect laboratory-reared green and northern leopard frogs experimentally were unsuccessful, suggesting rather narrow specificity for this parasite in ranids. Gametogenesis and sporogonic stages of this parasite were ultrastructurally similar to those described for Hepatozoon species. The parasite appears to be transmitted directly between bullfrogs and mosquitoes in the study area where Cx. territans feeds avidly on bullfrogs, which in turn were observed to naturally ingest these mosquitoes. Based on data presented in this study and the earlier description by Stebbins in 1903, the haemogregarine parasite of bullfrogs was designated as a new combination, Hepatozoon catesbianae.