Tsetse fly belongs to genus Glossina of family Glossinidae and is pronounced tse-tse or teet-see or set-see. They are large biting flies found in Africa that suck blood of vertebrates and transmit several protozoan diseases.
Tsetse flies are similar to other large flies but can be distinguished as they fold their wings completely when at rest so that one wing rests directly on top of the other. Adults are yellowish to brownish, with a piercing proboscis and a hatchet-shaped cell in the center of each wing. The arista of the third antennal segment has branched setae. Larvae breathe through a pair of posterior spiracles and in the third instar via a pair of lateral lobes, which contain three air chambers and open through numerous spiracles.
Female tsetse flies are viviparous, which involves the retention of a single egg that develops to the third larval stage before being deposited. The egg within the uterus hatches in 3–4 days, giving rise to the first instar larva that obtains nourishment from secretions of a pair of uterine glands from the mother. The larvae are deposited in soil where they burrow and feed and pupate for 4–5 weeks.
The young adult emerges from the pupa and both sexes suck blood. Males are not fully fertile until several days after emergence, and females are able to mate two to three days after emergence. The first larval offspring is deposited about 9–12 days after the female emerges. Tsetse flies females live up to 14 weeks while males live for around 6 weeks.
Tsetse flies have about thirty four species and sub-species that are placed in a single genus, Glossina. Some species transmit trypanosome species that cause trypanosomiasis or sleeping sickness in humans caused by Trypanosoma brucei gambiense and T. brucei rhodesiense. In animals, they transmit nagana, in cattle, horses, pigs and antelopes which is caused by Trypanosoma brucei brucei, T. congolense and T. simiae and surra in horses and pigs caused by Trypanosoma suis.
Tsetse transmit trypanosomes in two ways:
Mechanical transmission involves direct transmission of trypanosomes taken from an infected host into an uninfected host. The fly feeds on an infected host and acquires trypanosomes in the blood meal and then, if within a short period it feeds on an uninfected host and regurgitates infected blood and saliva into the tissue of uninfected animal, it has transmitted the protozoans.
Biological transmission requires a period of incubation of the trypanosomes within the tsetse stomach where the protozoans reproduce through several generations to become infective stage. Tsetse infected by trypanosomes are thought to remain infected for the remainder of their lives.