The vector (tsetse fly)
Trypanosomiasis is transmitted to man and animals by a blood sucking insect, the tsetse fly. Tsetse flies include all the species in the genus Glossina.
While tsetse flies resemble house flies, having a similar size ranging from 8 to 17 mm, two anatomical characteristics make them easily distinguishable while resting. Tsetse flies fold their wings completely so that one wing rests directly on top of the other over their abdomen and they have a long proboscis which extends directly forward and is attached by a distinct bulb to the bottom of their head.
Tsetse are believed to be extremely old insects since fossil tsetse have been identified from the Florissant Fossil Beds in Colorado and some species have also been described in Arabia. Today living tsetses are almost exclusively found on the African continent south of the Sahara. Some 29 to 31 species and sub-species (depending on classification) have been identified, however only 6 of them are recognized as vector of sleeping sickness and incriminated in the transmission of the two pathogenic human parasites.
The first continental wide distribution of tsetse flies was established by Ford and Katondo in the 1970s. More recently maps showing the predicted areas of suitability for tsetse flies have been produced for FAO by the Environmental Research Group Oxford (ERGO Ltd).
Transmission of trypanosomiasis involves four interacting organisms: the human host, the insect vector, the pathogenic parasite and the domestic and wild animal reservoirs. Glossina are efficient vectors and are responsible for linking these organisms and any reduction of their numbers should lead to significantly reduced transmission and hence contribute to HAT elimination and the sustainability of control efforts.