Electron microscope study of the cuticle of male and female Onchocerca volvulus from various geographic areas.

Male and female Onchocerca volvulus from Liberia, Upper Volta, Tanzania and Guatemala were examined by scanning and by transmission electron microscopy. In the cuticle of the female a basal, a median and a cortical layer can be differentiated. The outer limitation of the cuticle is an irregularly folded surface membrane. Excluding the anterior region the entire cuticle of the worm is covered by a coat. A regular fine honey-comb structure of the surface is found in the anterior region of the female. The morphology of the mouth, the amphidial openings, the papillae and the vulva, as well as the anus and the phasmidial openings, are presented. The cuticle of the male is also composed of a basal, a median and a cortical layer. The surface membrane shows a regular honey-comb pattern, which covers the entire worm with the exception of the anterior and posterior ends, but no coat was found. The cephalic region looks like that of the female. Papillae are arranged around the anus and the caudal tip. The variability of these papillae regarding their number and distribution is presented. The type of the two spicules and of the canal of the longer one is illustrated. The comparison of the worms from Liberia, Upper Volta, Tanzania and Guatemala revealed no morphological differences. Groups of males were examined statistically for differences of the distribution of the posterior papillae, but no geographical differences could be proven.