Endemic kala-azar in Eastern Sudan: A longitudinal study on the incidence of clinical and subclinical infection and post kala-azar dermal leishmaniasis

Between April 1991 and April 1993, a longitudinal study was performed in the village of Um-Salala (1,430 inhabitants) in the endemic area of kala- azar (visceral leishmaniasis) in eastern Sudan. During the two years, a total of 92 kala-azar cases were diagnosed (male:female ratio = 1.8:1, mean age 6.6 years). The annual incidence rates were 38.4/1,000 and 38.5/1,000 person- years, respectively. The ratio of clinical to sub-clinical cases was 1.6:1 in the first year and 2.4:1 in the second year. Post-kala-azar dermal leishmaniasis occurred in 48 (56%) of 85 kala-azar cases that were followed- up for at least six months. Kala-azar occurred only in previously leishmanin- negative individuals. The majority of the population had a positive leishmanin skin test result, probably due to previous exposure to Leishmania major causing cutaneous leishmaniasis in their homeland in western Sudan from which they had migrated in the 1980s. It was thus postulated that previous cutaneous leishmaniasis might protect against kala-azar but this could not be proved.