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Trypanosomes are elongated unicellular protozoal organisms with an undulating membrane and anterior flagellum.
The trypanosomes are transmitted by haematophagous insect vectors including the tsetse fly and triatomid kissing bug.
Stercorarian trypanosomes develop in the posterior gut of the insect and infective metatrypanosomes are excreted in the faeces of the insect onto the skin of the host.
They can then penetrate the tissues, gaining access through skin abrasions or mucous membranes. The metatrypanosomes then multiply within the reticulo-endothelial system of the host, later disseminating throughout the organs invading host cells residing within parasitophorous vacuole. These vacuoles acidify and subsequently release trypomastigotes into the cell cytoplasm. These then develop into amastigotes which divide several times eventually transforming back into trypomastigotes that rupture the host cell. From here they may invade other cells or enter the bloodstream where the opportunity may arise to infect the insect vector. The amastigotes may also burst the host cell and invade other cells.
T. cruzi, the trypanosome of most human importance, is a typical Stercorarian trypanosome and utilises the triatomid “kissing bug” as its vector among others. Disease in dogs may also occur.
Salivarian trypanosomes develop in the anterior gut of their vector, the Tsetse fly.
Development occurs in the proboscis and midgut, forming epimastigotes which then invade the hypopharynx and develop into trypomastigotes and then infective metatrypanosomes form.
These are then innoculated into the mammalian host through a bite before a blood meal.
Trypanosomes deplete carbohydrates, proteins, lipids and micronutrients from their hosts.
They cause haemolytic anaemia when present within the bloodstream.
Trypanosomosis affects the lymphoid and haematopoeitic systems of a wide range of hosts.
T. brucei affects all domestic mammals, including small and farm species, and humans. It also causes a specific skin disease in donkeys.
T. vivax infects ruminants, horses and camels causing significant disease.
T. equiperdum causes venereal equine disease dourine. It is the only trypanosome that does not immediately require an insect vector for transmission, being spread through coitus.
T. simiae causes fatal pyrexia in pigs while T. congolense is milder in the same species.
T. congolense can also affect dogs and cats causing acute fever, anaemia and neurological signs.
T. evansi also affects all domestic mammals.
T. cruzi occurs in South America where it is transmitted by a triatomid (kissing) bug and infects armadillos, possums and humans. It is known as Chagas’ Disease. A similar acute disease is thought to be caused by T. cruzi in dogs in the USA.
T. melophagum and T. theileri are non-pathogenic species present in the UK infecting cattle, buffalo and antelope. Stress and concurrent disease are thought to be contributors to the development of clinical disease from T. theileri.
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Datasheet(s) used: Trypanosoma accessed on 6 June 2011
This article has been expert reviewed by Nick Lyons MA VetMB CertCHP MRCVS
Date reviewed: October 29, 2011
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