Life histories, ultrastructure, molecular biology and phylogenetic relationships of Hepatozoon species, Phylum Apicomplexa, suborder adeleorina

grantor: University of TorontoThe life histories, morphology, ultrastructure, host-specificity and molecular biological characteristics of 'Hepatozoon' species infecting snakes from Ontario, Canada were investigated in order to elucidate typical life cycle patterns of these apicomplexan parasites, to determine which criteria are useful in describing species of 'Hepatozoon', and to formulate a phylogenetic hypothesis for species of this genus and related haemogregarines. The life cycle of a new species of haemogregarine, ' Hepatozoon' sipedon, the gamonts of which are intraerythrocytic parasites of Natricine snakes in Ontario, was observed to involve three hosts. Sporogonic development and the formation of large multisporocystic oocysts occurred in the haemocoel of mosquitoes of the genera 'Culex' and ' Culiseta' after these insects fed on infected snakes. Mature cysts containing two cystozoites, were observed in the liver of species belonging to three families of frogs and toads following the ingestion of infected mosquitoes. Two rounds of merogony occurred in various internal organs after snakes were fed frogs containing cysts of the parasite. Merozoites released after the second round of merogony entered erythrocytes and matured into gamonts. Electron microscopy revealed that both sporozoites and cystozoites contained lipid inclusions, amylopectin vesicles and a crystalloid body and that macromeronts and micromeronts were ultrastructurally similar except for the type and number of inclusions contained within immature meronts and merozoites. Host-specificity experiments showed that 'H. sipedon' and four morphologically similar forms from various regions of Ontario displayed a relatively high host- specificity for their mosquito hosts and a low host-specificity for their vertebrate hosts. Riboprinting and nucleotide sequence analysis of the first internal transcribed spacer (ITS-1), located between the 18S and the 5.8S ribosomal RNA genes, revealed that seven isolates of 'H. sipedon ' and similar forms from three different species of snakes in three distant localities were a single panmictic polymorphic species. A phylogenetic analysis of 'Hepatozoon' species and other haemogregarines, based on morphological, ultrastructural and developmental characters revealed that the genus 'Hepatozoon' is paraphyletic and that 'Hepatozoon' species have evolved with their arthropod definitive hosts. As well, guidelines for the preparation of 'Hepatozoon ' species descriptions, based on the evaluation of which criteria are necessary for defining species, and a systematic revision of the genera ' Hepatozoon' and 'Haemogregarina' were proposed.Ph.D