Some observations on onchocerciasis including sowda in the Yemen Arab Republic

A pilot study on onchocerciasis and sowda was carried out in the south-western region of the Yemen Arab Republic. Of 61 persons examined in eight villages 35 (= 57%) were found positive for microfilariae by the skin-snip method, 13 had typical manifestations of sowda, 17 had other onchocercal-suggestive skin lesions and five had subcutaneous nodules. A single larva of Simulium damnosum s.I. was collected in Wadi Barakani. Numerous larvae and pupae of S. ruficorne and S. hargreavesi were taken in fast-flowing streams in four localities. The examination of microfilariae and adult worms by scanning electron microscopy as well as the histochemical staining of microfilariae for the demonstration of acid phosphatase activity confirmed that the concerned filaria belongs to the species Onchocerca volvulus. No morphological differences could be detected between the smaller number of the examined worms from the Yemen and the extensive parasite material from Liberia, West Africa.