500 million years ago single-celled parasites called trypanosomes began their lives on Earth. 300 million years later, the tsetse fly evolved in what is now Africa and became the parasite’s main host. Humans and our ancestors, appearing around 5 million years ago, are new comers to this system.
Image of trypanosomes through a microscope
Pregnant female tsetse fly
Credit: Geoffrey M. Attardo
When a human is bit by an infected tsetse fly, the parasites multiply, causing headaches, fever, weakness, joint pains, swollen lymph nodes, and stiffness. The parasites spread into the brain and central nervous system where they cause sleep disorders, sensory disturbances, abnormal mobility, psychiatric disorders, seizures, coma, and death.
Trypanosomiasis was spread throughout and outside Africa through trade, human migration, colonization, imperialism, and the slave trade. People moved to new environments. Taxes required people to grow crops on new lands populated by tsetse flies. Forced labor and new transportation, like railways, increased the risk of moving trypanosomiasis from one area to another.
Map of tsetse fly range with contemporary national borders
Outside of the tsetse fly’s natural range, the disease was not able to sustainably spread very far. But, fluctuations in temperature, drought, famine, and flood allow tsetse flies and trypanosomes to move and settle into areas they have never been in before.
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Tsetse flies and trypanosomes are still around today. There are around 300,000 confirmed case of African trypanosomiasis each year.
Health workers screening for African trypanosomiasis in the Democratic Republic of the Congo