Trypanosomosis is a protozoal infection, which can occur in dogs and to a lesser extend in cats in many parts of the world. The disease is caused by protozoa of the genus Trypanosoma, which are mainly transmitted by tabanids, stable flies, tsetse flies or triatomines, depending on the species involved. Several other domestic and wild animals are also susceptible for clinical infections with trypanosomes. Furthermore some of the pathogens possess a zoonotic potential causing among others sleeping sickness in man. In ruminants and horses, the developing disease can be of massive economic importance and is restricting successful cattle farming in large parts of Africa. In dogs, the disease can be chronic or acute with a variety of symptoms and a potential lethal outcome. Some of the trypanosomes infecting dogs also possess an important zoonotic potential – with the presence of dogs as well as cats contributing significantly to increased domestic transmission (here for Trypanosoma cruzi) (Gürtler et al., 1993), causing Chagas disease in the Americas.


Trypanosoma parasites are flagellate protozoa belonging to the family Trypanosomatidae, which includes blood and tissue parasites of vertebrates, usually transmitted by blood-feeding vectors. Six trypanosome species are known to infect dogs: Trypanosoma brucei (brucei), Trypanosoma caninum (unknown pathogenicity), Trypanosoma congolense, Trypanosoma cruzi, Trypanosoma evansi and Trypanosoma rangeli (non-pathogenic). In cats, T. brucei (brucei)T. congolense and T. evansi have been reported as pathogens with possible clinical signs, whereas infection with T. cruzi is reported frequently, but without the clinical situation as described in dogs.

Trypanosomes are characterised by a longitudinal, fusiform appearance, a flagellum which arouses from the basal body moving forwards, an undulating membrane and a kinetoplast, lying behind the basal body.

The developmental cycle of trypanosomes is typically heteroxenous (that is, part of the cycle occurs in a vertebrate and part in an invertebrate host), although the cycle of one species (T. caninum) is still unknown.

A cyclic development takes place in the insect host. Trypomastigote forms are taken up by the insect during feeding on the vertebrate host. Depending on the species, the trypanosomes multiply within the insect host in different locations. At the end of the development, metacyclic forms are produced, which are then transmitted to a new host. Based on the mode of transmission, trypanosomes can be divided into the group of Stercoraria, when the pathogen is passed on through insect faeces, and of Salivaria, when transmitted via the saliva. In some species, a mechanical transmission may also occur.




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