Tsetse Flies

Tsetse flies are large, physically-tough biting flies that are common across Sub-Saharan Africa between the Sahara and the Kalahari deserts. They feed on the blood of vertebrate hosts and are vectors of the protozoan parasites trypanosomes which cause sleeping sickness in humans and nagana disease in cattle.

Tsetse flies belong to the genus Glossina in the family Glossinidae. The Glossina genus is split into three groups of species based on a combination of distributional, behavioural, molecular and morphological characteristics; these are savannah (Sub-genus Morsitans), riverine (Sub-genus Palpalis) and forest flies (sub-genus Fusca).

Adult flies are relatively large (0.5 to 1.5 cm) with a wide abdomen which is shorter than the wings. The wings are completely folded when resting so that one wing rests on top of the other over their abdomen. They also have a long and distinct proboscis which extends directly forward from the head, attached by a bulb at the bottom. Tsetse can take a blood meal equivalent to its own body weight. Tsetse flies can act as both mechanical and biological vectors of trypanosomes, acquiring and transmitting the protozoan parasites from an infected vertebrate host. These parasites, of the genus Trypanosoma, are approximately the size of a red blood cell and enter the sub-cutaneous tissue after a tsetse bite. The protozoa then move to the lymphatic system where they can progress to the bloodstream, cross into the central nervous system, invade the brain and lead to death if left untreated.

Much study has been carried out on tsetse flies and their control and due to the relatively low reproductive rate, and specific and well understood host-seeking cues, insecticide treated traps have been developed as highly effective control tools. Where necessary (e.g. over large inaccessible areas) the application of ULV insecticide may also be necessary.

> WHO – Human African Trypanosomiasis and control of Tsetse flies