PATHOGENS

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.