The burden of tropical diseases.

More than half the world's population is at risk of the tropical diseases malaria, leprosy, schistosomiasis, lymphatic filariasis, onchocerciasis, Chagas disease, African trypanosomiasis and leishmaniasis, and half a billion people are infected with at least one of these diseases. We present statistic on the population at risk and the infected population, and on the major morbidity and mortality attributable to each of these diseases. During the next decade the prevalence of leprosy, Chagas disease, and onchocerciasis is expected to fall, but for the other tropical diseases the epidemiological situation may remain stagnant or even worsen.