Sleeping sickness, formally known as Human African Trypanosomiasis (HAT), is a serious parasitic disease. It is caused by protozoan parasites from the genus Trypanosoma and transmitted to humans through the bite of an infected tsetse fly. HAT is found exclusively in specific regions of sub-Saharan Africa, where the tsetse fly vector is present. Without proper treatment, this condition is generally fatal.
How Sleeping Sickness Spreads
Sleeping sickness primarily spreads through the bite of an infected tsetse fly (genus Glossina). These flies acquire Trypanosoma brucei parasites from infected humans or animals. Once inside the fly, the parasites multiply and develop into a form that can be transmitted to a new host when the fly takes another blood meal.
There are two main forms of human African trypanosomiasis, each caused by a different subspecies of the parasite. West African sleeping sickness is caused by Trypanosoma brucei gambiense, which accounts for the vast majority of reported cases, around 92%. This form is prevalent in 24 countries across West and Central Africa and typically causes a chronic illness that progresses slowly, often over months or even years. Humans are the primary reservoir for T. b. gambiense, though animals can also carry it.
East African sleeping sickness, caused by Trypanosoma brucei rhodesiense, represents a smaller percentage of cases, about 8%. This more acute form is found in 13 countries in Eastern and Southern Africa. Symptoms emerge more rapidly, sometimes within weeks or a few months after infection, and the disease progresses quickly. Wild game animals, such as cattle, serve as the main reservoir for T. b. rhodesiense, making it primarily a zoonotic disease.
Recognizing the Signs
Sleeping sickness symptoms unfold in two distinct stages. The first stage, known as the hemolymphatic stage, begins after the parasite multiplies in the blood and lymph. Initial symptoms can include a transient chancre, a red sore that appears at the site of the tsetse fly bite within two to three days. This stage also commonly presents with general flu-like symptoms such as fever, headaches, and joint pain.
Swollen lymph nodes, especially in the neck, a condition often referred to as Winterbottom’s sign, are another characteristic manifestation of the first stage. Intermittent fever, muscle aches, and itching can also occur. During this phase, the parasites are circulating in the bloodstream and lymphatic system.
The second stage, or neurological stage, begins when the parasites cross the blood-brain barrier and invade the central nervous system. This invasion leads to more severe and characteristic symptoms, including profound sleep disturbances, such as excessive daytime sleepiness and nocturnal insomnia, which gives the disease its common name. Individuals may also experience confusion, poor coordination, and sensory disturbances. Other neurological signs can involve abnormal movements, tremors, difficulty walking, speech problems, and psychiatric changes.
Identifying and Treating the Disease
Diagnosing sleeping sickness involves identifying the Trypanosoma parasite in biological samples. Microscopic examination of blood smears, fluid aspirated from swollen lymph nodes, or cerebrospinal fluid (CSF) can reveal the presence of the parasites. The choice of sample depends on the suspected stage of the disease and the specific parasite subspecies involved. Early detection is important because treatment outcomes are better when the disease is caught in its initial stage.
Determining the disease stage is a crucial step before initiating treatment. This involves assessing whether the parasites have crossed the blood-brain barrier and entered the central nervous system. Lumbar puncture to collect cerebrospinal fluid is often performed to check for the presence of parasites or elevated white blood cell counts, which indicate neurological involvement. The specific drug regimen chosen depends entirely on this staging.
Treatment for the first stage, before neurological involvement, typically involves less toxic medications that are effective against the circulating parasites. For Trypanosoma brucei gambiense infections in the first stage, fexinidazole or pentamidine are commonly used. For Trypanosoma brucei rhodesiense infections in the first stage, suramin is the preferred treatment. These drugs aim to clear the parasites from the bloodstream and lymphatic system, preventing progression to the more severe neurological stage.
When the disease has progressed to the second stage and the central nervous system is affected, more potent drugs are required to cross the blood-brain barrier. Medications like melarsoprol, eflornithine, or nifurtimox-eflornithine combination therapy (NECT) are utilized for second-stage Trypanosoma brucei gambiense infections. Melarsoprol is a highly effective but toxic drug, while eflornithine and NECT offer safer alternatives. The specific choice of medication is based on the parasite subspecies, the stage of the disease, and drug availability.
Stopping the Spread
Controlling the spread of sleeping sickness involves a multi-pronged approach that targets the tsetse fly vector, protects individuals, and identifies infected people early. Vector control methods are a cornerstone of prevention. This includes deploying insecticide-treated targets and traps, which attract and kill tsetse flies, thereby reducing their populations in endemic areas. Additionally, targeted spraying of insecticides can help to suppress fly populations in specific high-risk zones.
Personal protective measures are also important for individuals living in or traveling to endemic regions. Wearing long-sleeved clothing and trousers can reduce exposed skin, making it harder for tsetse flies to bite. Using insect repellents containing DEET on exposed skin can also offer a layer of protection. Avoiding dense bush areas during the hottest parts of the day, when tsetse flies are most active, can further minimize exposure.
Surveillance programs are another key component of stopping the spread. These programs involve active screening of populations in areas where the disease is present. By systematically testing people for the presence of the parasite, infected individuals can be identified and treated early, even before symptoms become severe. This early diagnosis and treatment not only saves lives but also reduces the reservoir of infection, thereby limiting further transmission to tsetse flies and other people.