African trypanosomiasis

Lore & Background

African trypanosomiasis is caused by the protozoan Trypanosoma brucei, transmitted by the bite of an infected tsetse fly. Humans are infected by two subspecies: T. brucei gambiense, which causes over 92% of cases and is primarily transmitted between humans, and T. brucei rhodesiense, which is zoonotic with animals such as cattle serving as reservoirs. The disease occurs in two stages: the hemolymphatic stage, where parasites replicate in blood and lymph causing fever, headache, itchiness, and joint pains about one to three weeks after the bite; and the neurological stage, which begins weeks to months later when the parasite crosses the blood–brain barrier, leading to confusion, poor coordination, numbness, and trouble sleeping. The neurological stage gives the disease its common name of sleeping sickness due to sleep-wake disturbances.

Reader's Guide

African trypanosomiasis, or sleeping sickness, is caused by the protozoan *Trypanosoma brucei*, transmitted through the bite of an infected tsetse fly. Two subspecies affect humans: *T. b. gambiense*, responsible for over 92% of cases and spread mainly between people, and *T. b. rhodesiense*, a zoonotic form with animal reservoirs like cattle. The disease progresses in two stages. In the first, or hemolymphatic stage, parasites replicate in blood and lymph, causing intermittent fever, headache, joint pains, and swollen lymph nodes, often in the neck. Weeks to months later, the parasite crosses the blood–brain barrier, initiating the neurological stage with confusion, poor coordination, numbness, and sleep disturbances. Without treatment, the infection is almost always fatal. Diagnosis involves detecting the parasite in blood or lymph fluid; a lumbar puncture distinguishes the stages. *T. b. gambiense* causes a chronic infection taking months to years to develop symptoms, while *T. b. rhodesiense* progresses within weeks. Prevention focuses on avoiding tsetse bites through repellents and protective clothing, alongside vector control like insecticides and releasing sterilized flies. Screening at-risk populations with blood tests helps prevent severe disease. Treatment is easier early: pentamidine or suramin for the first stage, and eflornithine or nifurtimox-eflornithine combination for the neurological stage. Fexinidazole, an oral drug, treats either stage of *T. b. gambiense*. Melarsoprol works for both types but is reserved for *T. b. rhodesiense* due to severe side effects. The disease is endemic in sub-Saharan Africa, with over 80% of cases in the Democratic Republic of the Congo. Three major historical outbreaks occurred: 1896–1906 in Uganda and the Congo Basin, and two in 1920 and 1970 across several African countries. It is classified as a neglected tropical disease. In animals, the infection is called nagana.

Did You Know?

• Human African trypanosomiasis is also known as sleeping sickness.
• T. brucei gambiense causes over 92% of cases and is primarily transmitted between humans.
• Without treatment, African trypanosomiasis almost always results in death.
• More than 80% of cases are in the Democratic Republic of the Congo.

The Two-Stage Progression

The disease unfolds in two distinct phases. Initially, the parasite replicates within the bloodstream and lymphatic system, producing what is called the hemolymphatic stage. During this period—roughly one to three weeks after the tsetse fly bite for the rhodesiense form, and a longer, less precisely defined window for gambiense—patients experience intermittent fevers lasting a day to a week, separated by quiet stretches of days or even months. Severe headaches, joint aches, persistent itching, progressive weakness, and noticeable weight loss accompany these febrile episodes. As the infection advances, the parasite breaches the blood–brain barrier and invades the central nervous system, marking the meningoencephalitic or neurological stage. At this point, confusion, impaired coordination, numbness, and disrupted sleep patterns emerge. Critically, neurological symptoms can overlap with the earlier hemolymphatic phase, making it difficult to separate the two stages based on clinical signs alone. Without intervention, the disease is almost invariably fatal.

Clinical Hallmarks & Diagnostic Challenges

Several distinctive features help clinicians recognize the infection. A trypanosomal ulcer may appear at the bite site within two days, most commonly with rhodesiense infections and occasionally in gambiense cases, particularly among individuals from non-endemic regions. Lymph node swelling is another prominent sign; posterior cervical nodes at the base of the skull or along the back of the neck—known as Winterbottom's sign—are especially characteristic of gambiense disease, though axillary, inguinal, and epitrochlear nodes can also enlarge to striking sizes. Diagnosis typically relies on identifying the parasite in a blood smear or aspirated lymph node fluid, while a lumbar puncture helps determine whether the infection has crossed into the neurological stage. Complicating matters, the nonspecific early symptoms can be mistaken for malaria, which may co-occur. Travelers from non-endemic areas sometimes present atypically with fever, diarrhea, jaundice, and minimal lymphadenopathy, leading to delayed or missed diagnoses.

The Treatment Arsenal

Therapeutic options depend heavily on which subspecies is involved and how far the disease has progressed. For first-stage gambiense or rhodesiense infections, pentamidine or suramin remain the standard choices. Once the parasite has entered the central nervous system, eflornithine alone or in combination with nifurtimox is preferred. Fexinidazole, a newer oral agent, can treat either stage of gambiense disease, offering a significant practical advantage over injectable regimens. Melarsoprol, effective against both subspecies, carries severe side effects and is therefore generally reserved for rhodesiense cases. The overarching principle is that early detection—before neurological symptoms appear—makes treatment substantially easier and safer. Screening at-risk populations with blood tests for gambiense infection serves as a critical preventive strategy, catching the parasite during its chronic, slow-progressing phase before irreversible brain damage sets in.

Epidemiology & the Long Arc of Control

African trypanosomiasis persists across 36 sub-Saharan countries, with approximately 70 million people living in at-risk areas. The Democratic Republic of the Congo accounts for more than 80% of all cases. Vector control strategies, including insecticide spraying and the release of sterilized tsetse flies, have played a central role in reducing transmission. The disease is officially classified as a neglected tropical disease. Beyond humans, cattle and other livestock can harbor the parasite, a condition known as nagana or animal trypanosomiasis, which compounds the economic and agricultural impact in endemic regions.