''Hepatozoon'' is a genus of

Apicomplexa The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an ap ...

alveolates which incorporates more than 300 species of obligate intraerythrocytic parasites. Species have been described from all groups of tetrapod vertebrates, as well as a wide range of haematophagous

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s, which serve as both the vectors and definitive hosts of the parasite. By far the most biodiverse and prevalent of all haemogregarines, the genus is distinguished by its unique reciprocal trophic lifecycle which lacks the salivary transmission between hosts commonly associated with other apicomplexans. While particularly prevalent in amphibians and reptiles, the genus is more well known in veterinary circles for causing a tick-borne disease called hepatozoonosis in some mammals.

Lifecycle

Members of the genus ''Hepatozoon'' possess particularly complex lifecycles which vary considerably among species. Sexual reproduction and sporogenic development occur within the haemocoel of the invertebrate host, which is subsequently consumed by the vertebrate host. The

sporozoite Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organis ...

s then migrate to the liver of the vertebrate, where they undergo multiple fission (asexual reproduction) to produce merozoites. The meronts are released into the bloodstream where they form

gametocyte A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called ''spermatocytes'', and female gametocytes are called ''oocytes''. Development T ...

s, the final stage of development within the vertebrate host. The gamonts are large, conspicuous organisms which occupy a significant portion of the

erythrocyte Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood ce ...

, and are easily visible on simple blood films. When the invertebrate vector feeds on the blood of the infected vertebrate, the gamonts are taken up into the gut once more, where they undergo gametogenesis and the cycle begins once more. This simplified lifecycle is, of course, insufficient for species which infect vertebrate and invertebrate hosts which do not directly feed on one another, necessitating an even more complex cycle. For instance, '' Hepatozoon sipedon'' infects mosquitoes and snakes, but since snakes do not typically feed on mosquitoes, a third, intermediate host is required, in this case a frog. The frog ingests the infected mosquito, and the snake acquires the infection by feeding on the now-infected frog. Another mosquito can then feed on the snake, thus continuing the lifecycle. Hepatozoonosis, therefore, results when an animal eats an infected tick - the disease is not spread by tick bites. Species include '' Hepatozoon muris'' and '' Hepatozoon canis'', which typically infects mice and dogs, respectively, and '' Hepatozoon atticorae'', which is found in birds.

References

{{Taxonbar, from1=Q1153950, from2=Q15158354 Apicomplexa genera