The tsetse fly, a bloodsucking insect native to Africa south of the Sahara Desert, plays a significant role in public health. There are two to three dozen known species within the genus Glossina. These flies transmit a serious parasitic disease to both humans and animals.
Identifying Tsetse Flies and Their Habitats
Tsetse flies are robust insects, 6 to 16 millimeters (0.2 to 0.6 inches) long, resembling houseflies. Their coloration varies from yellowish-brown to dark brown, often with a gray thorax and dark markings. A distinguishing characteristic is their unique wing venation, which includes a “hatchet-shaped” cell in the center of their wings.
When at rest, tsetse flies fold their wings completely over their backs, a feature that sets them apart from other flies. They also possess a forward-projecting piercing proboscis, a stiff, needle-like mouthpart used for puncturing skin and feeding on blood. This proboscis is attached by a distinct bulb to the bottom of their head.
The genus Glossina is categorized into three ecological groups based on preferred habitats: the fusca (forest), morsitans (savanna), and palpalis (riverine) groups. Savanna species like Glossina morsitans thrive in drier regions of eastern and southern Africa. Riverine species such as Glossina palpalis are found near rivers and lakes in the humid environments of western and central Africa.
Tsetse flies inhabit dense forests, woodlands, and savannas. Their distribution is influenced by climate, vegetation, and the availability of host animals, including large mammals. While they occur in woodlands, they may venture into open grasslands if attracted by a host.
Transmitting African Sleeping Sickness
Tsetse flies are biological vectors for African Trypanosomiasis, a parasitic disease caused by Trypanosoma protozoans. This disease is known as African Sleeping Sickness in humans and Nagana in domestic animals. The fly transmits the parasite (Trypanosoma brucei) when it takes a blood meal from an infected host and then bites an uninfected one.
After an infected blood meal, trypanosomes multiply in the fly’s midgut for two to three weeks, then migrate to the salivary glands. When the infected fly bites a human, parasites are injected into the bloodstream, causing illness. Both male and female tsetse flies can transmit the infection.
Human African Trypanosomiasis (HAT) presents in two main forms, determined by the infecting parasite’s subspecies. Trypanosoma brucei gambiense causes West African sleeping sickness, accounting for 92% of reported cases and prevalent in 24 countries in West and Central Africa. This form causes a chronic illness, where individuals may be infected for months or years without significant symptoms.
The initial stage of T. b. gambiense infection involves trypanosome multiplication in subcutaneous tissue, blood, and lymph, leading to symptoms like intermittent fever, headache, enlarged lymph nodes, and joint pains. As the disease progresses, parasites cross the blood-brain barrier, entering the central nervous system. This second stage can lead to behavioral changes, confusion, sensory disturbances, poor coordination, and sleep cycle disruption, which gives the disease its name.
The second form, East African sleeping sickness, is caused by Trypanosoma brucei rhodesiense, accounting for 8% of cases and found in 13 countries in Eastern and Southern Africa. This form results in an acute disease, with initial signs and symptoms emerging within weeks or months after infection. If left untreated, both forms of HAT are fatal, with T. b. rhodesiense infections progressing more rapidly, leading to death within weeks to months, while mortality from untreated T. b. gambiense infection averages around three years after inoculation.
Protecting Against Tsetse Fly Bites
Protecting oneself from tsetse fly bites involves personal protective measures, as there is no vaccine or preventative drug for African sleeping sickness. Individuals should wear long-sleeved shirts and long pants made of medium-weight fabric, as tsetse flies can bite through thin materials. Neutral or light-colored clothing is recommended, as tsetse flies are attracted to bright colors, very dark colors, metallic fabrics, and blue.
Using insect repellents containing DEET (20% or greater concentration) can offer protection, though their effectiveness against tsetse flies can vary. Permethrin-treated clothing can also be used, or pre-treated clothing can be purchased. When using both sunscreen and repellent, apply sunscreen first, followed by the insect repellent.
Avoiding dense bush areas, particularly during the hottest parts of the day when flies may rest in shrubs, can reduce exposure. Tsetse flies are also attracted to moving vehicles; inspect vehicles before entering and keep windows wound up when slowing down or stopping in infested areas. If in an area with tsetse flies, tucking trouser legs into socks or boots can help prevent flies from getting under clothing.
Broader control efforts include insecticide-treated traps and lures, often dark blue or black, designed to attract and kill flies. Removing low brush around affected villages can also help manage tsetse populations. While these efforts reduce disease spread, individual precautions remain important for personal protection, especially for those in rural areas or travelers to endemic regions.