The tsetse fly, belonging to the genus Glossina, is an insect native to sub-Saharan Africa. These flies are narrow-bodied, ranging from 6 to 16 millimeters in length, and vary in color from yellowish-brown to dark brown with a gray thorax that may have dark markings. When at rest, their wings are held flat over their back, folded one over the other, a distinct characteristic that helps identify them. Both male and female tsetse flies feed exclusively on blood, making their bites significant for humans and animals.
Characteristics of the Bite
A tsetse fly bite can be painful. Immediately after the bite, a red, itchy welt or hive may appear at the site, which can be larger and more painful than a typical mosquito bite. Within about a week, a painful sore called a chancre may develop at the bite location. This chancre is an indurated, red nodule that can ulcerate. The localized reaction can also include swelling or blistering.
Risk of Disease Transmission
The primary concern associated with a tsetse fly bite is its role as a vector for Human African Trypanosomiasis (HAT), commonly known as sleeping sickness. This parasitic disease is caused by protozoan parasites of the genus Trypanosoma, specifically Trypanosoma brucei. The parasite is transmitted to humans when an infected tsetse fly takes a blood meal.
Not every bite from a tsetse fly will transmit the disease. Only a small percentage of flies in endemic areas are infected with the parasite. The risk of infection increases with more frequent bites. There are two main forms of HAT: West African sleeping sickness, caused by Trypanosoma brucei gambiense, and East African sleeping sickness, caused by Trypanosoma brucei rhodesiense.
Symptoms of African Trypanosomiasis
African Trypanosomiasis progresses through two distinct stages, with symptoms varying depending on the infecting Trypanosoma brucei subspecies. The first stage, known as the hemolymphatic stage, involves the parasite multiplying in the blood, lymph, and subcutaneous tissues. Early symptoms of this stage, which may appear within 1 to 4 weeks of infection, include intermittent fever, headaches, muscle and joint pain, and a transient rash.
During the hemolymphatic stage, generalized lymphadenopathy, or swollen lymph nodes, is common. A characteristic sign, particularly with Trypanosoma brucei gambiense infections, is Winterbottom’s sign, which involves enlarged, non-tender lymph nodes in the posterior cervical triangle, located at the back of the neck. Other symptoms can include malaise, pruritus, and facial swelling or organ enlargement like splenomegaly.
The second stage, the neurological stage, begins when the parasite crosses the blood-brain barrier and infects the central nervous system. This progression leads to severe symptoms. Sleep disturbances are a hallmark, manifesting as daytime sleepiness followed by nighttime insomnia. Other neurological symptoms include confusion, personality changes, irritability, tremors, and impaired speech.
Motor disturbances, such as ataxia (lack of muscle coordination), can also occur. If left untreated, the disease will continue to progress, leading to stupor, coma, and ultimately, death. The progression is slower with Trypanosoma brucei gambiense infection, taking months to years for central nervous system involvement, while Trypanosoma brucei rhodesiense infection progresses more acutely, with CNS invasion occurring within weeks to months.
Prevention and What to Do After a Bite
To minimize the risk of tsetse fly bites, preventive measures can be employed. Wearing long-sleeved shirts and long trousers made of medium-weight, thick fabric is advisable, as tsetse flies can bite through thin materials. Neutral-colored clothing, such as khaki, olive, beige, white, gray, or cream, is recommended, as these flies are attracted to bright, dark, and contrasting colors, especially blue and black.
Avoiding dense bush areas and woodlands is helpful, as tsetse flies rest in these environments. Inspecting vehicles for flies before entering and keeping car windows closed can prevent them from getting inside, as they are attracted to moving objects and the dust created by vehicles. While insect repellents containing DEET or permethrin-treated clothing may offer some protection against other insects, their effectiveness against tsetse flies can be limited.
If a tsetse fly bite occurs, cleaning the bite area is an immediate step. If you have been in an endemic area and subsequently develop any symptoms consistent with African Trypanosomiasis, it is important to seek prompt medical attention. Early diagnosis and treatment are important for a favorable outcome.