What is onchocerciasis?

Onchocerciasis is an infection caused by the roundworm Onchocerca volvulus. This condition can cause a rash, itching and sometimes with scarring along with eye symptoms that can result to blindness.

Globally, millions of individuals all over the world have onchocerciasis. In most cases, blindness is evident and a high percentage are visually impaired. Remember that onchocerciasis is the second leading cause of blindness worldwide.

How the condition spreads

Onchocerciasis spreads via the bite of the female blackfly that breed rapidly in flowing streams. The cycle of infection starts once a blackfly bites an infected individual and becomes infected with the immature forms of the worm or microfilariae where they develop into larvae in the fly. Once the fly bites another individual, larvae are passed into the skin.

The larvae move beneath the skin and form nodules where they develop into adult worms in 12-18 months. The adult female worms can live for up to 15 years in these nodules. After mating, the mature female worms lay eggs that develop into microfilariae that leave the worm.

What are the symptoms?


The symptoms of onchocerciasis occur when the microfilariae die. Their death can cause significant itchiness that might be the only symptom. Rashes with redness can also develop.

The symptoms of onchocerciasis occur when the microfilariae die. Their death can cause significant itchiness that might be the only symptom. Rashes with redness can also develop.

Over time, the skin becomes thick, rough and appear wrinkled. There is loss of pigment that manifest as patchy spots. The lymph nodes including in the genital area can become swollen and inflamed. The nodules that contain the adult worms might be seen or felt beneath the skin.

The visual issues can range from minimal blurring to total blindness. The eye might become inflamed or appear reddened. Being exposed to bright light can cause discomfort or pain.

If not treated, the cornea can turn completely opaque and even scar which is the cause for the blindness. The other eye structures including the pupil, iris and retina might also be affected. The optic nerve can become inflamed and degenerate. In addition, blindness can also result to a decreased life span.

How is it diagnosed

In most cases, a skin sample is taken and assessed for microfilariae. An alternative is blood testing but not always available or reliable. The microfilariae might also be seen in the eye using a slit lamp.

The nodules can be removed and analyzed for adult worms, but this is rarely needed.


  • Avoid areas that are infested by flies
  • Wear proper protective clothing
  • Apply insect repellants

Ivermectin that is given once or twice in a year can drastically minimize the number of microfilariae, prevents the development of further disease and controls the infection among those who were repeatedly exposed.

Management of onchocerciasis

The condition is treated using ivermectin in a single dose orally and repeated every 6-12 months until the symptoms are gone. Ivermectin works by killing the microfilariae, reducing their amount in the eyes and skin and cutting down the production of microfilariae by adult worms for several months. Just remember that it does not kill the adult worms, but repeated doses can reduce their fertility.

Oftentimes, the doctor might also provide doxycycline for 4-6 weeks. It eliminates some of the bacteria that thrive within the worm which are essential for their survival. As an outcome, the worms die. As for the side effects, they are usually mild. In the previous years, the nodules are removed surgically but the treatment has been replaced by ivermectin.



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