Infective larvae of Onchocerca volvulus
The third larval stage (L 3), infective larvae, are transmitted to humans by black fly bites. The disease caused by O. volvulus is called “onchocerciasis” or “river blindness. ”
Microfilaria of Onchocerca volvulus, from skin snip from a patient seen in Guatemala. Wet preparation. Some important characteristics of the microfilariae of this species are shown here: no sheath present; the tail is tapered and is sharply angled at the end.
A. Subcutaneous microfilariae of O. volvulus are demonstrated. Blindness may result from migration of larvae into the eye.
Onchocerciasis, or river blindness, is the result of infestation with the threadworm, Onchocerca volvulus, and is one of the leading causes of blindness in the developing world. After the entry of microfilaria into the skin via the bite of the simulium fly (black fly), subcutaneous nodules and an intense pruritic rash may develop. The adult worm lives tissues and discharges in cutaneous fibrous large numbers of microfilaria.
Onchocerca nodule on the trunk of a male from Sierra Leone. Several males and females of O. volvulus live in one nodule. Females produce hundreds of embryos daily. The embryos free themselves from shells and penetrate the ectodermal tissue, and many may remain trapped in the eye, where they eventually die.