The morphology of adult Onchocerca volvulus based on electron microscopy.

The fine structures of male and female O. volvulus are described. The sexual dimorphism and the age dependent modifications are mentioned in particular. The cuticle of the male worm consists of more layers than that of the female. The epicuticle of the male is wrinkled, whereas the epicuticle of the female forms protuberances. The outer membrane of the hypodermis is folded to form lamellae, which are associated with a layer of mitochondria. The female worms have only small somatic muscle cells. The intestinal cells are filled with concentric spherules, and the intestinal lumen is reduced. Various types of age dependent alterations of the fine structures are observed. The electron density of the cytoplasm changes. The interspace between basal lamina and cell membrane increases, the number of organelles is reduced and specific structures are decomposed whereas the number of granules, vacuoles and lipid droplets increases with age and the laminae and the cuticle thicken. These age dependent modifications might resemble drug induced alterations.