Trypanosomes infecting man and animals


African trypanosomes

The genus Trypanosoma is large and diverse. It includes several species that infect wild and domesticated animals in Africa, particularly hoofed animals, and humans. The African trypanosomes T. rhodesiense, T. gambiense, T. brucei, T. congolense, T. vivax and T. suis are all transmitted via tsetese flies (Glossina spp.). The species that cause human African trypanosomiasis ("sleeping sickness") also infect wild animals and can be transmitted from these animals to humans (zoonotic infections). As their name implies, most African trypanosomes are restricted to Africa, although a few species such as T. evansi and T. vivax, have been imported into South America. After a bloodmeal the bloodform trypanosomes, called trypomastigotes, transform and develop in the insect's midgut, first as procyclic insect stages. After some time they move to the proventriculus, where they transform to epimastigotes and from where they infect the salivary glands. Once in the salivary glands they transform to metacyclic trypomastigotes, which are infectious to the mammalian host. Once in the mammal they develop as long slender trypomastigotes, first in the area of the bite that becomes an ulcering chancre, from where they move towards the lymphe glands and the bloodstream, where they divide every 5-7 hours. In general this phase of the disease leads to recurrent attacks of fever and to the wasting (cachexia, loss of weight) of man and animal. From there the trypanosomes cross the blood-brain barrier to invade the central nervous system and this leads to the typical symptoms of sleeping sickness, i.e. a disturbed day and night rithm, change in personal character and coma. When not treated the course of the disease will be a fatal one resulting in death.


American trypanosomes

A few species of Trypanosoma are also found in the New World. T. cruzi, causing Chagas' disease in latin America is only distantly related to the African trypanosomes. It is an intracellular parasite that is transmitted via blood-sucking bugs (Triatoma). Chagas' disease is found throughout much of central and northern South America, Central America, and Mexico. T. cruzi is found in a number of animals other than humans, including dogs, cats and rodents, and the infection can be transmitted from these animals to humans.


Trypanosomes, their hosts and the diseasees they cause

 Host

 Parasite

 Disease

 Vector

 Man

T.rhodesiense
T.gambiense
T.cruzi

 Sleeping sickness

Chagas' disease

 Tsetse flies

Triatoma

 Cattle

T.rhodesiense
T.brucei
T .congolense
T.vivax
T.suis
(pigs only)

 Nagana

 Tsetse flies

 Equines

 T.equinum
T.equiperdum

 
Dourin (horses)

 None

 Camels

 T.evansi

 

Surra (camels)

 Tabanids

The trypanosomes of equines (T. equinum and T. equiperdum ) and of camels (T. evansi ) are not transmitted by tsetse but by direct blood contact during copulation (horses) or by biting insects such as horse flyes (tabanids). The latter serve as a natural syringe transmitting the trypanosomes from one host to the other while probing several animals, one after another, for blood. Here there is no need for the development of other life-cycle stages of the parasite in the insect. As a result the disease of camels and equines is also found outside the tsetse belt such as in the Sahara desert and even in Europe and the US. Interestingly, these trypanosomes have lost the capacity to activate mitochondrial activity, required for development in the fly midgut as a procyclic insect stage.


In addition to Africa, T. vivax is also found in the Americas, where it is transmitted by biting insects. Especially in large parts of South America, notably in the vast planes of the Brazilian Pantanal, T. vivax is causing disease in cattle herds.


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Last updated: 8 October 1997.

created by :Fred Opperdoes