''Hepatozoon'' is a genus of

Apicomplexa The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. Th ...

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

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

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 organism is ...

s then migrate to the liver of the vertebrate, where they undergo multiple fission (asexual reproduction) to produce merozoites. The

meront 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 organism is ...

s are released into the bloodstream where they form gametocytes, 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), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

, 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 Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic di ...

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