Onchocerciasis is a tropical disease transmitted by the Simulium species of the black flies. The black flies breed along fast-flowing streams, hence the name ‘river’ blindness. 
The disease ranks among the leading infectious causes of blindness in endemic areas. It is most common in remote villages, especially in West and Central Africa. It affects the skin, eyes and other body organs.

Also Known As

African river blindness

Causes and Risk Factors

Onchocerciasis is caused by a parasite known as Onchocerca volvulus (filarial worm). The parasite is transmitted to human beings via the black flies. The flies pass the worm's larvae to the human host as they feed on the blood meal. Once in the body, the larvae take about a year to mature to adult worms. 
Adult worms migrate to other parts of the body. They live in nodules under the skin or in the eyes. The females then fertilize and produce offspring (microfilariae). The microfilariae are usually underdeveloped and microscopic, and live in the blood. They are picked up by a black fly as it feeds. In the body of the fly, the microfilariae develop into mature larvae over close to two weeks. The larvae then make their way into the proboscis of the fly and are passed onto the next host. The cycle then continues.
Persons most at risk of the disease are those who live in the tropical areas where there is a prevalence of the black flies. Contracting onchocerciasis is not dependent on age or gender.

Signs & Symptoms

It takes repeated infections for individuals to experience the adverse effects of the disease. After the infection, symptoms don’t appear until 1 to 2 years later. They occur due to the inflammatory responses in the body which are most severe after the larvae die. The skin manifestations of the disease can appear as the first symptoms. These include:

  • Development of skin nodules (onchocercoma)
  • Itching (pruritus)
  • Papular rash
  • Scarring
  • Sagginess
  • Patchy depigmentation

Ocular manifestations of the disease may include eye lesions, redness, altered vision, and eventually, permanent blindness.


The diagnosis involves tests such as:
Skin snip biopsy – This is usually the most common test. It involves taking a small skin specimen and placing it in normal saline for 24 hours. The saline helps to draw out the larvae. Staining is also done to make it easier to detect the parasite through a microscope. The Onchocerca volvulus does not have a sheath or nuclei in the tail. Although it is used often, the biopsy test does not detect the parasite in the early stages of infection.
Slit-lamp test – The test uses a special kind of microscope (slit lamp) to view the back of the eye. It is useful in checking for the presence of larvae in the eye. It also examines the level of damage caused.
Examining nodules – The nodules on the skin can be surgically removed. They are assessed inside for presence of adult worms.
Antibody tests – The antibodies fight off infections in the body. The antibody test detects whether the body has tried to attack an onchocerciasis infection or not.


Treatment is focused on fighting the infection. It may also involve reverting complications that arise.

Medical Treatment

Ivermectin is prescribed as the first line of treatment for onchocerciasis. The drug works by killing the larvae and also sterilizing the female adults. Usually, a single dose is given every 6-12 months for about 10 years or so. The downside to the medication is that it does not eliminate the adult worms. 
Doxycycline is an antibiotic that has emerged in onchocerciasis treatment. The drug kills the bacteria (wolbachia) needed by the adult worms for survival. It may, however, need to be used in combination with ivermectin.

Surgical Treatment

Surgery may be necessary when complications are involved. Cataract extraction, for instance, may be performed where a cataract develops. A trabeculectomy may also be performed in case of glaucoma.

Prognosis/Long-term outlook

The prognosis is favourable where there’s early detection. Delayed treatment can lead to complications in the body. Corneal manifestations can include lesions which can lead to sclerosing keratitis and eventual blindness.
When the larvae invades the iris and ciliary body, it can result in iridocyclitis. Severe cases can result in glaucoma and cataract development. Those receiving treatment should go for eye check-ups as frequently as every 3 to 6 months for progress monitoring.


The strategies that can be used to prevent the infection include:
Personal protection – This includes avoiding infested areas, or using repellents and wearing appropriate clothing when in such places.
Controlling the vector – Spraying with insecticides helps control the flies and reduces the transmission of the parasite.
Mass treatment programs – In communities where the disease is prevalent, everyone can be treated with ivermectin to fight any light infections as well as to stall the life cycle of the disease.