Hepatozoon
Encyclopedia
Hepatozoon is a genus of Apicomplexa
n protozoa 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
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 life cycle which lacks the salivary transmission between hosts commonly associated with other apicomplexans. While particularly prevalent in amphibian
s and reptile
s, the genus is more well known in veterinary circles for causing a tick
-borne disease called hepatozoonosis in some mammal
s.
of the vertebrate
, where they undergo multiple fission (asexual reproduction) to produce merozoites. The meronts are released into the bloodstream where they form gametocyte
s, the final stage of development within the vertebrate host. The gamonts are large, conspicuous organisms which occupy a significant portion of the erythrocyte, 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 life cycle 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 mosquito
es and snake
s, 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 life cycle.
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 brds.
Apicomplexa
The Apicomplexa are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as flagella or...
n protozoa 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
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
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 life cycle which lacks the salivary transmission between hosts commonly associated with other apicomplexans. While particularly prevalent in amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, the genus is more well known in veterinary circles for causing a tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
-borne disease called hepatozoonosis in some mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s.
Life cycle
Members of the genus Hepatozoon possess particularly complex life cycles 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 sporozoites then migrate to the liverLiver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
of the vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
, where they undergo multiple fission (asexual reproduction) to produce merozoites. The meronts are released into the bloodstream where they form gametocyte
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....
s, the final stage of development within the vertebrate host. The gamonts are large, conspicuous organisms which occupy a significant portion of the erythrocyte, and are easily visible on simple blood films. When the invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
vector feeds on the blood of the infected vertebrate, the gamonts are taken up into the gut once more, where they undergo gametogenesis
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 division of diploid gametocytes into various gametes,...
and the cycle begins once more.
This simplified life cycle 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 mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es and snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, but since snakes do not typically feed on mosquitoes, a third, intermediate host is required, in this case a frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
. 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 life cycle.
Hepatozoonosis, therefore, results when an animal eats an infected tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
- the disease is not spread by tick bites. Species include Hepatozoon muris and Hepatozoon canis, which typically infects mice
MICE
-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...
and dogs, respectively, and Hepatozoon atticorae, which is found in brds.