Life cycles, morphological characteristics, and host specificity of Hepatozoon species infecting eastern garter snakes from Ontario

The life cycles of species of Hepatozoon that occur naturally in eastern garter snakes, Thamnophis sirtalis sirtalis, were studied in the mosquito Culex pipiens in various amphibians, including northern leopard frogs, bullfrogs, gray treefrogs, American toads, and blue-spotted salamanders, and in natricine snakes, including northern water snakes and northern brown snakes. Morphological features of the oocysts of two forms of Hepatozoon from various widely separated regions of Ontario differed with respect to the number of sporozoites per sporocyst and the diameter and shape of the oocyst. However, morphological and morphometric differences were not apparent in the cystic or merogonic stages in the vertebrate hosts. Cystic stages of these haemogregarines were found in the liver of all four species of anurans, but not in salamanders. These forms were transmitted experimentally to garter, water, and brown snakes, with gamonts appearing in erythrocytes 45 days after the snakes were fed infected anurans. A comparison of these forms of Hepatozoon with previously named species of ophidian haemogregarines from North America indicates that there are at least two, and likely more, species of Hepatozoon in Ontario.