Rapid assessment of the geographical distribution of Mansonella perstans infections in Uganda, by screening schoolchildren for microfilariae.

The geographical distribution of Mansonella perstans infections in Uganda was assessed by day-time examination of school-aged children for microfilariae. Overall, 12,207 children from 76 sites representing the various topographical and ecological zones in the country were examined. Children with M. perstans microfilaraemia were detected at 47 (61.8%) of the study sites, with prevalences ranging from 0.4% to 72.8%. A broad, east-west-oriented belt of high endemicity was identified, stretching across the central part of the country from the southern end of Lake Albert to the north-western shores of Lake Victoria. To the north and south of this belt prevalences generally decreased, although high-prevalence foci were also identified in the far north-western and south-eastern corners of the country. Geostatistical interpolation was used to create a map showing the geographical distribution of M. perstans prevalences in Uganda (by ordinary kriging), and to assess the population exposed to M. perstans transmission. Estimates based on population data from 2002 indicated that 20.4 million people (82.6% of the national population) and 6.8 million people (27.5% of the national population) lived in areas where, respectively, >1% and >10% of the school-aged children had M. perstans microfilaraemias. Since the prevalence of M. perstans microfilaraemia is known to increase with age, the overall population prevalences are likely to be even higher than the prevalences observed in the school-aged children. More attention needs to be paid to the public-health implications of this wide-spread but neglected infection.