Onchocerciasis, or river blindness, is an infection caused by a roundworm, Onchocerca volvulus. It is responsible for intense itching, a rash, sometimes with the formation of scars, swelling of the glands, visual disturbances or even complete blindness. This infection is transmitted by the bite of a female black fly, which breeds in streams. If onchocerciasis causes symptoms, treatment is a single dose of ivermectin, repeated every 6 to 12 months until symptoms resolve.

Onchocerciasis is a parasitic disease affecting the eyes and skin caused by a heartworm, a worm scientifically named Onchocerca volvulus. It is transmitted to humans through the bites of an infected small black fly called a blackfly.

Onchocerciasis is also called “river blindness” because these flies breed in rough waterways and the disease increases the risk of blindness in people living nearby.

Around 18 million people have onchocerciasis worldwide. Almost 270 of them are blind and 000 have visual impairments. Onchocerciasis is the second leading cause of infectious blindness worldwide.

Almost 90% of onchocerciasis cases occur in sub-Saharan Africa. It is also found in Yemen, southern Mexico, Guatemala, Ecuador, Colombia, Venezuela and Brazil along the Amazon.

The cycle of infection begins when a blackfly bites an infected person and becomes infected with immature forms of the worm called microfilariae. These develop as larvae in the fly. When the fly bites another person, the larvae pass into that person’s skin. The larva moves under the skin and forms nodules, where it transforms into an adult worm within 12 to 18 months. Adult females of these worms can live in these nodules for up to 15 years. After mating, mature females produce eggs, which turn into microfilariae which are expelled by the worm. A worm can produce 1 microfilariae per day. Thousands of microfilariae migrate through the tissues of the skin and eyes and it is these that are responsible for the disease.

Usually, for the infection to develop and cause symptoms, the person must have been bitten many, many times. For this reason, the infection is unlikely to appear in people who travel to areas where the disease is prevalent.

The death of microfilariae is very toxic to the skin and eyes. She provokes :

• persistent and unbearable itching;
• rashes with redness;
• over time, the skin may thicken, become rough, and wrinkle;
• loss of elasticity of the skin;
• depigmentation by forming uneven spots;
• inflammation and enlargement of the lymph nodes, including those in the genital area;
• inflammation in the eyes that turn red;
• onset of pain upon exposure to bright light;
• eye damage causing visual disturbances.

Without treatment, the cornea becomes completely opaque and scars can form. There may be damage to other structures of the eye, including the iris, pupil, and retina. Inflammation can develop in the optic nerve, causing it to degenerate.

After many years of exposure, these disorders can lead to irreversible blindness and unsightly skin lesions sometimes called “leopard skin” or “lizard”. In severe cases, people can develop long folds of skin that hang over the lower part of the abdomen (“hanging lower abdomen”) and upper thighs. In some communities in West Africa, around 50% of men over 40 have gone blind from the disease.

The following measures can help reduce the risk of blackfly bites and therefore the risk of onchocerciasis:

• avoid areas infested by flies;
• wear protective clothing;
• use insect repellents or even insecticides that are safe and harmless to the environment.

Onchocerciasis is treated with ivermectin (Mectizan®) which is a medicine to:

• paralyze and kill microfilariae, thereby reducing their number in the skin and eyes;
• relieve intense itching on the skin;
• stop the progression to blindness;
• reduce the production of microfilariae by adult worms for several months, thereby reducing transmission.

As part of the treatment for onchocerciasis, a single dose of ivermectin is taken orally every 6 to 12 months until symptoms resolve.

Onchocerciasis can also be treated with doxycycline given for 6 weeks. This antibiotic kills bacteria that live in worms and are essential for their survival. As a result, many adult female worms die, and others produce fewer, if any, microfilariae.