Léger proposed this taxon in 1911. The first species identified was Dactylosoma ranarum by Lankester (1871) 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 (Rhipicephalus sanguineus). The genus Hepatozoon was created by Miller in 1908 for a parasite of the white rat (Rattus norvegicus) 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.
All species in this suborder use the syzygy method 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 (and often several) 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 endodyogeny and the enclosure of sporozoites in a sporocyst.
In haemogregarines with heteroxenous species, conjugation of gamonts and subsequent sporogony usually occurs within an invertebrate (definitive host), 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 (Dactylosoma, Haemogregarina)
Ingestion — the parasite is transmitted by the ingestion of the infected invertebrate host by the vertebrate host. The mode of transmission may even involve a paratenic host. The next definitive host in the life cycle is infected exclusively through blood feeding. Examples include the genera Karyolysus, Hemolivia and Hepatozoon.
The taxonomy is this group may be incorrect as the Hepatozoidae appear to be paraphyletic.[2] The genus Hemolivia appears to lie within the genus Hepatozoon.[3] The genus Hepatozoon appears to have two subgenera with one in the carnivorous mammals and the other in lower vertebrates and rodents.[4]
Karyolysus infects lizards (Lacerta) and possibly scincids. Haemogregarina infects turtles and leeches. Species of the genus Desseria infect fish and lack erythrocytic merogony. The genera in the subfamily Ithaniinae share a number of morphological features and infect the digestive tract of insects.
DNA studies suggest Hemolivia may lie within the Hepatozoon clade.[3] If this can be confirmed, the taxonomy of this group will need revision. A study of the 18s rRNA gene suggests that there may be some overlap between Karyolysus and Hepatozoon.[6]
Karadjian, Chavatte and Landau revised the Adeleidae in 2015,[7] performed a molecular analysis and proposed a new classification in four 'types' based on their biology, as follows:
^Mathew JS, Van Den Bussche RA, Ewing SA, Malayer JR, Latha BR, Panciera RJ (April 2000). "Phylogenetic relationships of Hepatozoon (Apicomplexa: Adeleorina) based on molecular, morphologic, and life-cycle characters". J. Parasitol. 86 (2): 366–72. doi:10.1645/0022-3395(2000)086[0366:PROHAA]2.0.CO;2. PMID10780559. S2CID24122100.
^ abBarta JR, Ogedengbe JD, Martin DS, Smith TG (2012). "Phylogenetic position of the adeleorinid coccidia (Myzozoa, Apicomplexa, Coccidia, Eucoccidiorida, Adeleorina) inferred using 18S rDNA sequences". J. Eukaryot. Microbiol. 59 (2): 171–80. doi:10.1111/j.1550-7408.2011.00607.x. PMID22313415. S2CID205760200.
^Criado-Fornelio A, Ruas JL, Casado N, et al. (February 2006). "New molecular data on mammalian Hepatozoon species (Apicomplexa: Adeleorina) from Brazil and Spain". J. Parasitol. 92 (1): 93–9. doi:10.1645/GE-464R.1. PMID16629322. S2CID6713713.
