Trypanosomiasis is a protozoan parasitic disease of vertebrate animals and man, with a high mortality rate among domestic animals. Trypanosomiases are single cell parasites which are transmitted from the faeces of infected animals to flies which reinfect animals and man. Flies may also become reinfected from the blood of infected animals. The disease in wild animals is usually benign, as they develop a certain immunity, although this is rarely complete. Domestic animals, especially those raised for meat and milk-production are highly susceptible. Those severely affected are cattle, camels and pigs.
There are many species of trypanosomiasis which exist in all continents. The highest incidence of trypanosomiasis (gambiense and rhodesiense in man; vivax, congolense and simiae in animals) is in Africa, where it is transmitted particularly by the tsetse fly. There are four main varieties of infection: 'nagana' and 'surra' which particularly affect domestic animals; 'dourine' which affects equidae; 'sleeping sickness' which affect man. 'Nagana', 'sleeping sickness' and 'dourine' are the most important African varieties. There are 50 million people at risk and it is estimated that there are about 25,000 new infections in man per year.