Onchocerciasis situation in the Tukuyu focus of southwest Tanzania after ten years of ivermectin mass treatment.

A purposive cross-sectional epidemiological study was conducted in the Tukuyu Onchocerciasis focus in south-western Tanzania in 2004, ten years after launching the ivermectin mass treatment programme, and 23 years after establishing focal parasite prevalence. The objective was to assess contemporary Onchocerciasis clinical and parasitological situation and assess community knowledge about the disease and its control. From historical data, five villages with high parasite prevalence were selected, two each on the Lufilyo and Kiwira Rivers and one on lower Lumbira River. Skin biopsies were taken from the iliac crest on the left and right buttocks, for examination of Onchocerca volvulus microfilariae. Onchocercal skin lesions were checked using natural light, while nodules were palpated from head to ankles and scored. A structured questionnaire was administered to participants. A total of 438 persons (age=16-99 years) were examined. No skin microfilariae (mf) were detected. Onchocercal skin symptoms were found in 170 (38.8%), of which 30 (6.9%) had nodules, 48 (11.0%) chronic onchodermatitis and 92 (21%) itching. One-third (34.5%) had correct knowledge that black flies ("tusunya") are vectors of onchocerciasis. Half of the respondents (n=217) confirmed taking ivermectin for onchocerciasis treatment, and 428 (97.7%) were willing to continue for any duration. It is concluded that the undetectable skin microfilariae in the study sample was partly attributable to the consequences of ongoing ivermectin mass treatment. It is recommended that the control efforts, as well as monitoring and evaluation be sustained to determine its long term impact, and that a more sensitive technique be used to check O. volvulus skin mf prevalence.