Oncocercoza

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.

Onchocerca microfilariae A. Subcutaneous microfilariae of O Onchocerca microfilariae 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 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.

Onchocerciasis The patient shows atrophic dermatitis, connective tissue loss, glossy wrinkled skin, and multiple small nodules plus excoriations due to scratching. There is an intense pruritic reaction to the migrating larvae over a long period of time.

Depigmentation of skin (leopard skin) on an onchocercal patient Depigmentation of skin (leopard skin) on an onchocercal patient. The skin loses its elasticity and has a scaly appearance. The dead filarial bodies cause itching.

Onchocerciasis. A. Two boys in Central America show skin nodules (onchocercoma) typical of infection with Onchocerca volvulus. The nodules contain adult onchocerca, usually surrounded by a fibrous reaction. B. Excision of a subcutaneous nodule is shown.

Blindness due to onchocerciasis Blindness due to onchocerciasis. Microfilaria migrate into the conjunctiva and cornea, resulting in blindness.

This man is completely blind in the right eye and has blurry vision in the left eye. River blindness is a progressive chronic disease. The eye damage is irreversible even after removal of adult worms and microfilariae from the tissues.