The burden of Onchocerca volvulus in Sudan.

Onchocerciasis has been reported in Sudan since 1908 and now prevails in three endemic regions known as the southern, northern and eastern foci. The southern focus is the largest, with nodule and blindness rates exceeding 80% and 12%, respectively, in certain villages. Onchocercal infection in this region causes only a mild skin reaction although microfilarial loads in the skin are high. In contrast, those with onchocerciasis in the northern focus, located between the fourth and fifth Nile cataracts, present with limited but severe skin reactions, low nodule rates (16%), low microfilarial loads in the skin and no ocular involvement. The characteristics of patients from the eastern focus, close to the border with Ethiopian border are similar to those in the north, although most onchocercal skin disease in this area comprises the severe localized pruritus known as sowda.