What is Onchocerciasis?

NewsGuard 100/100 Score

Onchocerciasis, which is also known as river blindness, is an infectious condition of the skin and eyes that is caused by the parasitic worm Onchocerca volvulus. Onchocerciasis is transmitted by the bite of a blackfly (genus Simulium) that is infected with the parasite, usually in regions with a fast-flowing river or stream.

The vast majority of cases occur in African countries, although the disease does exist in other areas of the world, such as Latin America.

Treating and eliminating onchocerciasis

Onchocerca life cycle

For a human to become infected with onchocerciasis and symptoms to present, a number of steps must occur. Onchocerciasis begins with an infected blackfly (genus Simulium) biting a human host, thus introducing third-stage filarial larvae into the subcutaneous skin tissues of the human. The larvae will develop into adulthood, called filariae, and can reside in nodules in the skin for approximately 15 years.

These nodules contain both male and female filariae and can produce millions of larvae, called microfilariae, which have a lifespan of one to two years. These microfilariae can be found in connective tissues, skin, blood, urine, and sputum.

Onchocerca volvulus. Image Credit: Kateryna Kon / Shutterstuck.com

To repeat the transmission and spread of the infection to other individuals, a blackfly will need to bite a human host and ingest microfilariae. The microfilariae will then migrate from the gut to the thoracic muscles of the blackfly.

From this point, microfilariae will develop into third-stage infective filarial larvae and migrate to the proboscis of the blackfly. The infected blackfly will then repeat the cycle by biting a human host and subsequently introducing third-stage filarial larvae into the subcutaneous skin tissues of the human.


Individuals who have been infected with onchocerciasis do not experience symptoms initially, as the infection requires time to grow and spread. The larvae mature into adults within one year of introduction and live in nodules in the skin for approximately 15 years.

The nodules are usually found near the hips, pelvis, ribs, shoulder blades, and skull. It is these areas that are initially affected by symptoms, such as:

  • Itching of skin
  • Nodules under the skin
  • Rough or coarse skin
  • Hyperpigmentation of skin
  • Eye lesions
  • Vision changes

Without treatment, significant changes to the skin may be noted, including roughness, coarseness, and hyperpigmentation.

After continued severe infection, eye lesions may occur, caused by the death of larvae in the eyes. The resulting small opaque spots on the cornea can lead to the cloudiness of vision or loss of vision. As a result of this, onchocerciasis is the second leading cause of blindness due to an infectious disease, after trachoma.


People infected with onchocerciasis will not show signs of the condition immediately; therefore, diagnosis is often made 3 to 15 months after the initial infection.

Localized dermatitis or subcutaneous nodules may be visible upon physical examination and a biopsy of the affected area can be analyzed for the presence of microfilariae in a laboratory.

If onchocerciasis is suspected, nodules can be removed and analyzed to identify adult worms. For mild infections, a polymerase chain reaction can be used to diagnose the infection, although this method of diagnosis is costly.


Treatment for onchocerciasis involves the eradication of microfilariae, as the current treatments that target adult worms are toxic for humans.

Ivermectin is recommended for patients with the condition, as it is safe and effective. As this agent targets microfilariae, it reduces the reproduction of the worms and the disease does not progress.

However, treatment is required on a long-term basis, as adult female worms can continue to reproduce microfilariae, usually for 10 to 15 years. Standard treatment is once per year, although some patients require more frequent dosing.


Further Reading

Last Updated: Sep 9, 2022

Yolanda Smith

Written by

Yolanda Smith

Yolanda graduated with a Bachelor of Pharmacy at the University of South Australia and has experience working in both Australia and Italy. She is passionate about how medicine, diet and lifestyle affect our health and enjoys helping people understand this. In her spare time she loves to explore the world and learn about new cultures and languages.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Smith, Yolanda. (2022, September 09). What is Onchocerciasis?. News-Medical. Retrieved on May 24, 2024 from https://www.news-medical.net/health/What-is-Onchocerciasis.aspx.

  • MLA

    Smith, Yolanda. "What is Onchocerciasis?". News-Medical. 24 May 2024. <https://www.news-medical.net/health/What-is-Onchocerciasis.aspx>.

  • Chicago

    Smith, Yolanda. "What is Onchocerciasis?". News-Medical. https://www.news-medical.net/health/What-is-Onchocerciasis.aspx. (accessed May 24, 2024).

  • Harvard

    Smith, Yolanda. 2022. What is Onchocerciasis?. News-Medical, viewed 24 May 2024, https://www.news-medical.net/health/What-is-Onchocerciasis.aspx.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.