To the Editor: Mycobacteriumulcerans disease, commonly calledBuruli ulcer, is an emerging infectiousdisease in West Africa (1,2). Severalforms of Buruli ulcer exist; large,chronic ulcerations or induratedplaques of the skin are the most fre-quent manifestations of the disease(1), and bone is sometimes involved(3). Little is known about the focalepidemiology of Buruli ulcer; inci-dence, prevalence, and other data areusually reported at the national or dis-trict level (4). These data convey theimportance of the disease but do notshow the wide variations that occur atthe village level within a givendistrict. In 2002, we investigatedthe disease in an arrondissement(Gnizounmè) in an area in whichBuruli ulcer is endemic, the communeof Lalo in Benin. Prevalence rates ofBuruli ulcer varied from 0.58 to 32.62per 1,000 inhabitants of villages in thesame arrondissement. For GnizounmèArrondissement, the overall preva-lence was 10.70 per 1,000 inhabitants.These results confirmed that distribu-tion of Buruli ulcer must be deter-mined at geopolitical divisions lowerthan district or national levels, as isfrequently assumed to be the case.An inverse relationship existsbetween the prevalence of Buruliulcer and distance from the CouffoRiver, which drains the arrondisse-ment of Gnizounmè. A comparison ofthe relevant data for Assogbahoué andTandji villages shows that the numberof patients per 1,000 inhabitantsincreases gradually from 0.58 to32.62 as the distance from the riverdecreases from 10 to 1 km.Recently, aquatic insects havebeen considered potential vectors ofM. ulcerans (5,6). These aquaticinsects can fly many kilometers fromtheir source (7). This finding may par-tially explain how patients who livefarther distances from their source ofwater become infected, but not asoften as those who live closer. Somewater bugs obtained from water col-lection points along the Couffo Riverin the village of Tandji were found tobe positive for M. ulcerans by usingPCR with specific insertion sequence2404 as a target (8).
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