African trypanosomiasis, also called sleeping sickness is a disease caused by a parasitic pathogen, the protozoan haemoflagellate, known by the genus name Trypanosome. The protozoan cause of sleeping sickness was established in 1902-3 by Aldo Castellani and David Bruce in the course of studying a major Ugandan epidemic. Classical human sleeping sickness is restricted to those parts of sub-Saharan Africa where the insect vector the so-called tsetse fly, which transmits the trypanosome, is prevalent, i.e. western, eastern and central Africa. Twentieth-century knowledge, therefore, declares the aetiology of sleeping sickness to be specific to certain locations but to have no relation to particular kinds of (African) bodies. (Trypanosomiasis. Encyclopedia article; The Columbia Encyclopedia, Sixth Edition, 2004)
The single-celled trypanosomes that cause sleeping sickness spend their time cycling between humans and tsetse flies. They linger in the gut of the fly, absorbing amino acids and other molecules that the fly gets by biting mammals. After about ten days the trypanosomes move into the fly's salivary glands.
To prepare for their new home, the parasites cloak themselves in a coat made of millions of copies of a single sugary molecule. Our immune cells fashion antibodies that correspond to this molecule's shape, and the antibodies enable the immune system to kill the parasite in huge numbers. But some individual trypanosomes take evasive action. They shut down the genes they use to build their coat and turn on a new set in their place. They can then build a new surface molecule, one similar enough to the old one to do the job but which no longer matches the antibodies. Now invisible, the parasite thrives while the immune system starts a new eradication campaign from scratch. But trypanosomes have hundreds of coat-coding genes that they hold in reserve, and they can easily continue to slip away from the body's attack........
