Observations and reflections on the immature stages of Onchocerca volvulus in the human host.

Knowledge of the morphology, migrations and development rates of the L3, L4 and prepubertal L5 stages of Onchocerca volvulus in the vertebrate host is an essential prerequisite to work vaccine development of chemoprophylaxis. After a brief review of the scanty literature available on this subject a description is given of two immature worms, one male and one female, found in an O. volvulus nodule from Guatemala. The male, which measured 12 mm x 40 micron(s), had fine regular transverse cuticular annulations, two prominent spicules, and an undifferentiated testis. The female, which measured 20 mm x 40 micron(s), had not yet developed cuticular ridges but showed a vulva, gut, and two rudimentary genital tracts. It is thought that these worms may have been six to 12 weeks old. The likely course of the early development of O. volvulus in the vertebrate host is discussed, based on analogy with O. lienalis in cattle; and some of the factors to be taken into account when pursuing the search for O. volvulus immatures are described.