1. Epidemiological observations

Abstract A brief account is given of the geographical features of the Turkana area and of the events which led to the discovery that this part of Kenya had the highest incidence of clinically recognized hydatid disease in man anywhere in the world. Observations were made on the distribution of the disease following an aerial survey designed to determine the distribution of the people. It was found that the highest incidence of 198 surgical cases per 100,000 people per annum was in the north-western area bordering on the Sudan, Ethiopia and Uganda and this area was selected for the pilot control programme. By the development and assessment of better serodiagnostic methods combined with the use of a mobile ultrasound machine it has been shown that the true prevalence of hydatid disease in Turkana is between 5 and 10%. Studies on the parasite and its transmission have revealed that the species in Turkana is Echinococcus granulosus and that dogs and jackals are the main definitive hosts. Although goats, sheep, cattle and camels are all infected with hydatid cysts, dogs and jackals are also thought to be infected by scavenging on human corpses. In contrast to Masailand where wild carnivores and wild herbivores are infected, there is no wild life cycle in Turkana. The unusually high prevalence in man is thought to be due to the close intimacy of the Turkana with their dogs and to customs relating to the handling of dog faeces. Advances in immuno-differentiation and the use of DNA probes for distinguishing Echinococcus from taeniid eggs are likely to provide new tools for the diagnosis of infection in dogs and jackals and for studying the dispersal of eggs in the environment.