Coccidia

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Coccidia
Eimeria maxima oocysts

Eimeria maxima oocysts

Systematics
without rank: Diaphoreticks
without rank: Sar
without rank: Alveolata
without rank: Apicomplexa
without rank: Conoidasida
without rank: Coccidia
Scientific name
Coccidia
Leuckart , 1879

Coccidia (coccidia or Coccidiasina) are a subset of the Apicomplexa belonging Conoidasina , which usually intracellular parasites in higher animals, opportunistic but also live in humans.

The coccidia predominantly infect the gastrointestinal tract and, depending on the severity of the infestation, cause diarrhea . The diseases caused by coccidia are called coccidiosis . They occur in domestic animals such as dogs, cats and rabbits, but also in ruminants, poultry, fish and reptiles. So-called coccidiostats are administered as therapy. The disease can heal quickly after successful treatment. In special cases, e.g. B. in young animals, it can also be fatal.

Propagation cycle

In a host cell , usually in the gastrointestinal tract , blood , liver or kidney , they carry out asexual reproduction in the form of a schizogony / merogony (splitting) through multiple nuclear divisions and thereby destroy the cell. Each of the so-called merozoites (up to 100 from a parent cell) then infects a new cell and the process is repeated. The form of division depends on the parasite: Toxoplasma gondii divides in a form called endodyogeny , while Eimeria has a schizogony / merogony division pattern. In Sarcocystis , the pattern of division is called endopolygonia .

The number of asexual reproductions is specific for each coccidia species. Following the asexual reproduction phase (schizogony), sex cells ( gametogony ) are formed, namely large plasma-rich macrogametes and small flagellated microgametes, and sexual reproduction takes place . The fertilized female cell (zygote) surrounds itself with a shell (enzystation) and becomes an oocyst . It is excreted with the host's faeces . In the outside world there is reduction division (meiosis), in which mononuclear division products (sporoblasts) form and surround themselves with shells, the so-called spores ( sporogony ). The infectious sporozoites form in the spores with a further division (mitosis). In Sarcocystis , sporulation takes place in the host, the oocyst envelope breaks open before it leaves the intestine and sporocysts are excreted.

Systematics

The Coccidia are divided into two subgroups:

Adeleida (Adeleorina)

Micro- and macrogametocytes lay against each other before the mature sex individuals develop (synzygy). The species Adelea ovata attacks millipedes , Adelina dimidiata lives in centipedes ( Skolopender ); Klossia helicina lives in the kidney tissue of the Roman snail ( Helix pomatia ). Karyolysus species live in lizards and snakes, transmitted by mites.

Eimerida (Eimeriorina)

The Eimerida taxon has the following structure:

Eimerida species are the typical pathogens of coccidiosis (see above) in cattle, sheep, pigs, goats, rats, rabbits , but also in poultry, reptiles, amphibians and fish. Two Isospora species ( Cystoisospora belli ) are known from the human intestine. Leucocytozoon attacks the blood of birds. Eimeria goes through one-host (monoxene) life cycles and differs from Toxoplasma gondii , Sarcocystis and Plasmodium , which go through heteroxene (multi-host) cycles.

Cryptosporidia ( Cryptosporidium ) often infect calves, occasionally humans, and up to 40 other vertebrates.

Caryospora bubonis , a parasite of the Eimeriidae, attacks birds.

Parasites from the Frenkelia taxon, for example Frenkelia microti, infest birds as main hosts and rodents as intermediate hosts.

Toxoplasma gondii also belongs to the Sarcocystidae , so far the only species within the genus Toxoplasma. T. gondii is the causative agent of toxoplasmosis in cats. This infection is not dangerous for people with healthy immune systems. However, there is a risk in people with a weakened immune system (HIV or transplant patients). Another danger arises from the initial infection during pregnancy, in which the unborn child can die or become severely disabled.

Haemosporidia

Haemosporidia was wrongly assigned to the coccidia for a long time, but in the current systematics they belong to the class of Aconoidasida within the Apicomplexa . Haemosporidia is a group of parasites that is important to humans and includes the malaria pathogen Plasmodium malariae . Plasmodia are also the tropica parasite ( Plasmodium falciparum ) and the tertian parasite ( Plasmodium vivax ). Other plasmodia are found in monkeys, bats and other mammals, e.g. B. Theileria parva ( coastal fever of African cattle).

literature

  • Alfred Kaestner: Textbook of Special Zoology ; Vol. I invertebrates. Gustav Fischer, Stuttgart 1965, p. 85 ff.

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