Visceral leishmaniasis in Ethiopia. III. The magnitude and annual incidence of infection, as measured by serology in an endemic area.

A serological study of visceral leishmaniasis was carried out in a cohort of people in an endemic area of Ethiopia. The people were tested three times, at 6-monthly intervals. Seroprevalence at the start was 112 per 1000, and the annual rate of conversion from negative to positive was estimated as 106 per 1000. Both seroprevalence and incidence of seroconversion increased with age, and males showed higher rates than females, with a male:female ratio of seroconversion of 2:1. Accumulation of 6-monthly seroconversion rates was considered to give a better estimate of the annual rate itself, as the half-life of positive serology was only around 3 months.