Léger proposed this taxon in 1911. The first species identified was Dactylosoma ranarum by Lankester in a frog in Europe. It was initially called Undulina ranarum, but this was changed in 1882 to Drepanidium ranarum. This species was subsequently moved to the genus Dactylosoma. Canine hepatozoonosis was first described in India in 1905 by James. The organism was named Leukocytozoon canis. The vector was identified in 1907 by Christopher to be the brown dog tick. The genus Hepatozoon was created by Miller in 1908 for a parasite of the white rat that underwent merogony in the liver and sporogony in the miteLaelap echidinus. Ledger initially placed this genus in the family Haemogregarinidae, but Wenyon subsequently removed it and placed it in the newly created taxon Hepatozoidae in 1926.
Life cycle
All species in this suborder use the syzygymethod of gamete formation. This involves the association of often motile gamonts prior to the formation of functional gametes and fertilization. Their life cycles tend to be complex, involving at least one asexual cycles of merogony followed by gametogony, syngamy and sporogony. In many species of the group, the meronts and merozoites have morphologically distinct types: one type of meront produces large merozoites which initiate a further round of merogonic replication; a second produces smaller merozoites which are the progenitors of the gamonts. Microgamonts produce usually only one to four microgametes. Other characteristic features include the absence of endodyogony and the enclosure of sporozoites in a sporocyst. In haemogregarines with heteroxenous species, conjugation of gamonts and subsequent sporogony usually occurs within an invertebrate, which also serves as the vector. Merogonial division usually takes place in the parenchymatous organs of the vertebrate host. This is followed by the formation of infective gametocytes in the erythrocytes. In the genus Hepatozoon, gametocytes are also formed in the leukocytes. The haemogregarines use two modes of transmission:
Inoculation — the infectious sporozoites enter the vertebrate host during blood-feeding of the vector
Haemogregarines — heteroxenous coccidians cycling between blood-sucking invertebrates and various vertebrates — Dactylosomatidae, Haemogregarinidae, Hepatozoidae and Karyolysidae
One exception to this classification is known: Klossiella is a monoxenous coccidium of mammals and reptiles. The taxonomy is this group may be incorrect as the Hepatozoidae appear to be paraphyletic. The genus Hemolivia appears to lie within the genus Hepatozoon. The genus Hepatozoon appears to have two subgenera with one in the carnivorous mammals and the other in lower vertebrates and rodents.
