The origins of a new Trypanosoma brucei rhodesiense sleeping sickness outbreak in eastern Uganda

Background Sleeping sickness, caused by two trypanosome subspecies, Trypano soma brucei gambiense and Trypanosoma brucei rhodesiense, is a parasitic di sease transmitted by the tsetse fly in sub-Saharan Africa. We report on a r ecent outbreak of T b rhodesiense sleeping sickness outside the established south-east Ugandan focus, in Soroti District where the disease had previou sly been absent. Soroti District has been the subject of large-scale livest ock restocking activities and, because domestic cattle are important reserv oirs of T b rhodesiense, we investigated the role of cattle in the origins of the outbreak. Methods We identified the origins of cattle entering the outbreak area in t he 4 years preceding the outbreak. A matched case-control study was conduct ed to assess whether the distance of villages from the main market involved with restocking was a risk factor for sleeping sickness. We investigated t he spatial clustering of sleeping sickness cases at the start of the outbre ak. Findings Over 50% (1510 of 2796) of cattle traded at the market were report ed to have originated from endemic sleeping sickness areas. The case-contro l study revealed that distance to the cattle market was a highly significan t risk factor for sleeping sickness (p<0.001) and that there was a signific ant clustering of cases (27 of 28) close to the market at the start of the outbreak (p<0.001). As the outbreak progressed, the average distance of cas es moved away from the cattle market (0.014 km per day, 95% CI 0.008-0.020 km per day, p<0.001). Interpretations The results are consistent with the disease being introduce d by cattle infected with T b rhodesiense imported to the market from the e ndemic sleeping sickness focus. The subsequent spread of the disease away f rom the market suggests that sleeping sickness is becoming established in t his new focus. Public health measures directed at controlling the infection in the animal reservoir should be considered to prevent the spread of slee ping sickness.