Visceral leishmaniasis in Ethiopia. IV. Prevalence, incidence and relation of infection to disease in an endemic area.

In a population of some 4600 people in southern Ethiopia, in which visceral leishmaniasis is endemic, 142 cases were recorded in an 8-year period to 1990. The cases were very unequally distributed between the six villages studied, with more than 90% in the four which were closest to the uninhabited valley of the Segen River. It was deduced that transmission occurs in the villages at lowest altitude, as well as in the Segen Valley. The youngest children were rarely affected and half as many cases were females as males. In a year-long intensive study, annual incidence of disease was estimated at 6.9/1000 in the whole population. Incorporating the results of previously published immuno-epidemiological studies, the annual incidence of disease in susceptible people was calculated as 1.9% while the rate of immunoconversion was 5.6 times greater. This indicates a high incidence of abortive or cryptic cases, but it remains to be demonstrated whether or not these cases are sources of infection.