The tsetse fly (Glossina) is an insect primarily known for its role in disease transmission. These flies are between 0.25 to 0.6 inches (6 to 16 mm) in length, resembling a common housefly but with distinct features. When resting, their wings overlap completely over their back, creating a scissor-like appearance. They also possess a long, needle-like mouthpart called a proboscis that projects forward. Both male and female tsetse flies feed exclusively on blood, obtained by piercing the skin of vertebrate animals.
Global Distribution of Tsetse Flies
Tsetse flies are found exclusively on the African continent, inhabiting much of tropical Africa. Their distribution extends across 34 countries, from approximately 15° north in Senegal to about 28.5° south in South Africa’s KwaZulu-Natal Province. This broad geographical range is not uniform; tsetse flies are confined to specific “fly belts” across sub-Saharan Africa.
The most widespread species include Glossina palpalis and Glossina tachinoides in Western Africa, Glossina fuscipes in Central Africa, and Glossina morsitans and Glossina pallidipes in Eastern and Southern Africa. While comprehensive data exists for many regions, information on tsetse fly presence is limited for countries such as Angola, the Congo, the Democratic Republic of the Congo, and South Sudan. Published data are absent for Burundi, Guinea-Bissau, Liberia, Sierra Leone, and Somalia, though these countries are still considered affected.
Preferred Habitats and Microclimates
Tsetse flies occupy a variety of habitats within sub-Saharan Africa, from dense rainforests to open savannas. Their presence is closely linked to land cover characteristics, influenced by climate and human activities. Temperature and humidity significantly impact tsetse fly populations, with high temperatures and dryness limiting their spread at the edges of their distribution.
Different species groups of tsetse flies exhibit distinct habitat preferences. The fusca group inhabits rainforests or isolated forest patches, including riverine forests within savanna zones. The palpalis group prefers gallery forests, swamps, and watersides with closed canopies. The morsitans group is found in open woodlands and woodland savannas, but can also occur at forest edges, scattered thickets, and open country.
Within these broader habitats, tsetse flies seek out specific microclimates that offer cooler or more humid conditions, especially during harsh seasons or hot times of the day. These microhabitats provide refuge, enabling the flies to survive. Human-modified landscapes, such as farms and plantations, can also serve as suitable habitats for tsetse flies, particularly in the rainforest belt of West Africa.
The Link Between Location and Disease
The geographical distribution of tsetse flies directly correlates with the occurrence of African Trypanosomiasis, known as sleeping sickness in humans and nagana in animals. This parasitic disease is transmitted when an infected tsetse fly, carrying Trypanosoma parasites, bites a human or animal. The parasites are injected through the fly’s saliva during feeding.
The disease is prevalent in rural areas of sub-Saharan Africa where tsetse flies are found. For instance, Trypanosoma brucei rhodesiense, which causes East African sleeping sickness, is found in countries like Malawi, Tanzania, Uganda, and Zambia. Trypanosoma brucei gambiense, responsible for West African sleeping sickness, is found in Angola, the Central African Republic, Chad, the Democratic Republic of Congo, the Republic of Congo, Sudan, and Uganda. The presence of these specific tsetse fly species in particular regions dictates where humans and livestock are at risk of contracting trypanosomiasis.