Sleeping sickness works by hijacking the brain's internal clock
A tsetse fly bite can deliver a single-celled parasite that eventually slips past the blood-brain barrier. Once inside, it scrambles the genes that keep the body's daily rhythm, flipping sleep to daytime and wakefulness to night. Without treatment the disease is almost always fatal, yet deaths have fallen roughly tenfold since 1990.
The culprit is Trypanosoma brucei, in two human-infecting forms. The gambiense type passes mainly between people and causes over 92 per cent of cases, typically as a slow infection lasting months or years; the rhodesiense type lives in animal reservoirs such as cattle and strikes within weeks. In livestock the disease is known as nagana. Farmers, fishers and hunters in rural sub-Saharan Africa face the highest exposure.
Illness unfolds in two phases. First the parasites multiply in blood and lymph, bringing intermittent fever, severe headaches, itching and swollen glands; enlarged lymph nodes along the back of the neck, called Winterbottom's sign, are especially typical of the gambiense form. Later, after roughly 21 to 60 days for rhodesiense or 300 to 500 days for gambiense, the parasite invades the central nervous system. Because symptoms of the two stages overlap, doctors rely on a lumbar puncture to check spinal fluid, since the right drug depends on whether the brain is involved. Early symptoms are vague enough to be confused with malaria.
The disease's name comes from what happens next. Patients develop fragmented, inverted sleep, dozing through the day and lying awake at night, alongside confusion, tremor and sometimes psychiatric symptoms. Research indicates the parasite disrupts rhythmic expression of clock genes in the suprachiasmatic nucleus, the brain's master timekeeper, with inflammation adding to the damage. Notably, sleep patterns can return to normal after treatment, suggesting the clock is hijacked rather than destroyed. In infected mice, the ability to sustain REM sleep was reduced.
About 70 million people in 36 countries are considered at risk, with more than 80 per cent of cases in the Democratic Republic of the Congo. Deaths dropped from 34,000 in 1990 to around 3,500 in 2015, and only 583 confirmed cases were recorded in 2024. Insect repellents, insecticide spraying, releases of sterilised flies and blood screening have driven the decline, and fexinidazole now offers an oral treatment for either stage of the gambiense form.
Source: African trypanosomiasis
