Onchocerciasis (River Blindness) in Africa: Cause, Prevention and Treatment


By: Elizabeth Obigwe. Datelinehealth Africa Volunteer Freelance Writer, with medical review and editorial support from The DLHA Team


African man blinded by onchocerciasis

Image showing the eyes of an African man blinded by onchocerciasis



  • Onchocerciasis is also called “River blindness” because it is caused by the blackfly which is found close to flowing water.
  • The disease affects both the eyes and skin of patients.
  • Onchocerciasis is a Neglected Tropical Disease and the second infectious cause of blindness after trachoma.
  • More than 99% of people infected with onchocerciasis live in 31 countries in Sub-Saharan Africa.
  • Treatment of onchocerciasis can last up to 10 to 15 years





Although it is commonly called “river blindness”, onchocerciasis affects not only the eyes but also the skin and other organs in the body. 


On the skin, this disease causes obvious irritations and rashes among other symptoms. 


Unlike most eye diseases that affect specific parts of the eye, onchocerciasis affects several tissues in the eye from the external eyelid, through the conjunctiva and cornea (the transparent tissues covering the white and black part of the eyes) to the internal retina (the part of the eye responsible for image formation).



What Is Onchocerciasis?


Onchocerciasis is an infectious disease that affects both the eyes and skin and can lead to blindness and permanent skin damage. It is caused by the filarial worm (Onchocerca volvulus) that is transmitted by repeated bites of infected blackflies (Simulium spp.). 


Its common name “river blindness” is because the blackflies are mainly found around rivers and fast-flowing water. This disease is most common in Africa, especially in places with high poverty levels, low sanitation and poor healthcare facilities.


Onchocerciasis is the second leading infectious cause of blindness in Africa after trachoma. It is also one of the neglected tropical diseases that the WHO hopes to eradicate by 2030.



What Causes Onchocerciasis?

A blackfly on a surface

Fig. 1 showing the blackfly that transmits Onchocerciasis volvulus

This disease is caused by a parasite worm (Onchocerca volvulus). The worm is transmitted to humans by the blackfly which is mostly found during the day around flowing water. 


The female blackflies feed on humans to ingest blood which they need for ovulation. 


If the fly bites an infected person and then goes on to bite a non-infected person, it transfers this parasite from the former to the latter.  And this leads to the spread of the disease. 


These flies may also feed on the blood of animals like cattle and they can also infect them with onchocerciasis or cause fatal allergic reactions.


It is important to note that a single exposure to the vector may not cause onchocerciasis. It takes repeated bites by the blackfly for you to get infected.



What is the life cycle of onchocerciasis like?


Onchocercial larvae develop both in the backfly and in the human host (See fig. 2 for a summary of the O. volvulus life cycle).

Life cycle of O. volvulus


  1. Once the fly bites the skin of an infected host and ingests any O.volvulus that is in the blood pool, the microfilaria (the early stage of the parasite) gets into the stomach of the fly.
  1. Some ingested microfilariae eventually find their way to the flight muscle of the fly and develop into larvae.  
  1. The larvae then travel to the mouth part of the black fly.
  1. From here, the larvae can be transmitted to another human if the fly bites the person. 
  1. The larvae develop in the newly bitten person into mature worms.
  1. The adult female worms produce microfilariae that can be sucked up from blood by the blackfly following a bite and the cycle continues.


The entire development process of the onchocerca larvae within the fly takes between 6 to 9 days.

In its new host, the microfilaria develops into an adult worm within 6 to 12 months. 

Most of these adult female worms live in some sort of protective nest called the nodule which are found under the skin or near muscles and joints. The male worms on the other hand stay close to the female ones and migrate into the nodules to fertilize their female counterparts. 

It takes about 12 to 18 months after initial infection for the larvae to become detectable in the skin. 

In the skin, the larvae have a lifespan of about 12 to 15 months while the adult worm has a lifespan of about 10 to 15 years.



What are the symptoms of onchecerciasis?


Onchocerciasis triggers a number of symptoms in infected persons. But some people may not experience symptoms because the larvae can migrate to different parts of the body without triggering the immune system.


Most symptoms of onchocerciasis occur due to the body’s response to dead or dying larvae.


Onchocerciasis symptoms typically manifest in the eyes and skin.


The Eyes


Both dead and living larvae of the parasite affect the eyes, resulting in a condition called onchocercal eye (ocular) disease. 

The effect of onchocerciasis on the eyes is usually ongoing and involves a wide range of symptoms. 

Similarly, visual damage resulting from the condition can affect all parts of the eyes and the tissues within the region. 


The noticeable symptoms of the disease in the eyes include:  


  • Itching
  • Redness
  • Pain
  • Sensitivity to light
  • Diffuse keratitis
  • Blurring of vision

Appearance of eye disease caused by onchocerciasis


  • Corneal scarring
  • Night blindness
  • Intraocular inflammation
  • Glaucoma
  • Visual field loss
  • Blindness


Figure 3: Showing different levels of eye damage caused by onchocerciasis


The Skin


Skin-related symptoms usually manifest long before those of the eyes. 

They also range from mild to severe and affect different parts of the skin. These symptoms include: Skin nodules of onchocerciasis patient

  • Nodules: They appear in different sizes and you can see them and feel them under the skin. These nodules harden as they get older.
  • Itching
  • Skin rash
  • Swelling and inflammation of the skin
  • Sores on the skin
  • Skin discolouration
  • Dry and rough skin
  • Atrophy (thinning of the skin)
  • Papules (small raised bumps)
  • Formation of scales or flakes
  • Skin blistering
  • Skin ulceration
  • Skin thickening and scarring
  • Enlarged groin

The damages done by onchocerciasis are ongoing and may become irreversible - especially damages to the eyes. Hence, early detection and treatment is important. 

If you notice any of the signs and symptoms of the disease, see your doctor immediately. 



What Are the Risk Factors of Onchocerciasis?


People living in rural communities of countries where onchocerciasis is common are at risk of infection, especially those who live close to flowing rivers and streams.


Also, people on long-term visits to these areas such as missionaries, researchers and volunteers are likely to get infected.



How Can I Prevent Onchocerciasis?


The best method for the prevention of onchocerciasis is to avoid being beaten by a blackfly. 


If you live in an area that is not affected by this fly, you are not likely to get the disease. 


But for people living in these areas who have a higher risk of getting infected, some protective measures include:

  1. Always wear clothes that cover up your body well, including your arms and legs
  2. Ensure that your clothes are treated with permethrin insecticide
  3. Apply insect repellent to the exposed area of your body.



How Is Onchocerciasis Diagnosed?


A doctor trained in tropical diseases is best suited to make a diagnosis of onchocerciasis. 


After obtaining information about your complaints and asking several questions about your illness, the doctor will perform a general examination and then do any or all of the following specific tests in order to confirm the diagnosis.


  1. Skin snip test: The doctor takes a small sample of skin from the affected person using a tiny knife or needle. This skin sample is then examined under a microscope to check for the presence of the parasite's larvae (microfilariae).


  1. Serological tests: These tests involve taking a blood sample from the person suspected of having onchocerciasis. The blood is checked for the presence of specific antibodies that the body produces in response to the parasite. These antibodies help indicate whether the person has been exposed to the parasite.


  1. Polymerase chain reaction (PCR) test: This test involves collecting a skin sample or a small amount of blood. The DNA of the parasite is then analyzed using a special technique called PCR. It helps to identify the presence of the parasite's genetic material and confirm the diagnosis.


  1. Visual examination: Doctors may visually inspect the skin and eyes for characteristic signs of onchocerciasis. This includes looking for skin nodules, rashes, depigmentation, or other skin abnormalities. Eye examinations may be conducted to assess visual acuity and signs of ocular damage caused by the infection.


  1. Split lamp examination: This is a diagnostic procedure where a general doctor or specialist eye doctor (ophthalmologist) uses a specialized instrument called a slit lamp to closely examine the front structures of the eye. By focusing a bright light beam and using high magnification, the doctor can identify specific signs and abnormalities related to onchocerciasis-related eye disease. This examination helps assess the impact of the infection on the eye and guide appropriate treatment decisions.



How Is Onchocerciasis Treated?


If you are diagnosed with onchocerciasis, your doctor will prescribe a medication called Ivermectin

Ivermectin tabs.This medicine comes in the form of tablets or pills and you will need to take it once a year or as advised by your healthcare provider. It's important to follow the prescribed onchocerciasis treatment schedule.


Ivermectin works by killing the immature worms (microfilariae) in your body. However, it does not kill the adult worms but stops them from producing more microfilariae. This reduces the number of larvae and helps prevent the worsening of symptoms. 

Because adult worms live for as long as 10 to 15 years, you will have to be on treatment for that long to ensure complete eradication of the parasite from your system. Regular treatment helps control the infection and prevent further complications. 


Alternatively, your healthcare provider may treat you by combining Ivermectin with another drug called Doxycycline. Doctors say that treatment with doxycycline can kill adult worms by killing the bacteria (Wolbachia) on which they depend for survival.


Before a patient starts receiving any treatment, it should be confirmed that the person is not infected with Loa loa which is another parasitic filarial worm found in some areas where O. volvulus is found. Treating a person who has Loa loa with the medication for onchocerciasis can result in adverse side effects.  


African countries endemic to Loa loa are:

  • Cameroon
  • Central African Republic
  • Congo
  • Democratic Republic of the Congo
  • Nigeria and
  • South Sudan.


It's crucial to complete the full course of treatment as prescribed by your doctor, even if you start feeling better. This helps ensure the effectiveness of the medication and reduces the risk of complications.

Regular treatment and preventive measures can help control and manage onchocerciasis effectively. Preventive measures are important to help prevent new infections.



What are the public health issues in the control of Onchocerciasis?


According to the World Health Organization, more than 99% of infected people live in 31 countries in Sub-Saharan Africa (See list in Table 1). 


Two countries in Latin America  (the Yanomani area in Brazil and Venezuela) and Yemen also have cases of this disease. 


Also, globally, about 21 million people are estimated to be infected with onchocerciasis.


  1. Angola
  2. Benin
  3. Burkina Faso
  4. Burundi
  5. Cameroon
  6. Central African Republic
  7. Chad
  8. Republic of Congo
  9. Côte d’Ivoire
  10. Democratic Republic of the Congo
  11. Equatorial Guinea
  12. Ethiopia
  13. Gabon
  14. Ghana
  15. Guinea
  1. Guinea-Bissau
  2. Kenya
  3. Liberia
  4. Malawi
  5. Mali
  6. Mozambique
  7. Niger
  8. Nigeria
  9. Rwanda
  10. Senegal
  11. Sierra Leone
  12. South Sudan
  13. Sudan
  14. Togo
  15. Uganda
  16. United Republic of Tanzania

Table 1: List of sub-Saharan African counties where onchocerciasis (river blindness) is common.


WHO recorded that in 2017, at least 220 million people globally required preventive chemotherapy against Onchocerciasis, 14.6 million of the infected people already had a skin disease and 1.15 million had vision loss. 


Given these high numbers, a lot of work still needs to be done towards education and the eradication of this disease from Africa. 


Research carried out in the southwestern part of Nigeria revealed that proper information dissemination is needed as a core part of any elimination program and onchocerciasis public health control.





In spite of the large number of people living with and at risk of onchocerciasis, the WHO has put great effort into the elimination of the disease. 


Programs like Onchocerciasis Control Programme (OCP) and African Programme for Onchocerciasis Control (APOC) have helped to relieve millions of people from infection and saved a million others from blindness. It is through programmes like this that countries like Colombia, Ecuador, Mexico, and Guatemala which were once endemic regions became free. 


Unfortunately, onchocerciasis has become a Neglected Tropical Disease (NTD) and so adequate attention has not been given to the condition in endemic African regions. 


Even though the prevalence of onchocerciasis has reduced greatly in many African countries like Ghana, there are still significant cases in several countries of the region. 


Hopefully, with the new roadmap set by the WHO for controlling NTDs, the endemic African countries will achieve their goal of eradicating the disease.




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3. Onchocerciasis (river blindness). World Health Organization. Available from: https://www.who.int/news-room/fact-sheets/detail/onchocerciasis  Accessed May 23, 2023.

4. Onchocerciasis (river blindness). World Health Organization; https://www.who.int/health-topics/onchocerciasis#tab=tab_3. Accessed May 23, 2023. 

5. Marie C, William A. Petri J. Onchocerciasis (river blindness) - infectious diseases. MSD Manuals; 2023. https://www.msdmanuals.com/professional/infectious-diseases/nematodes-roundworms/onchocerciasis-river-blindness. Accessed May 23, 2023. 

6. Brattig NW, Cheke RA, Garms R. Onchocerciasis (river blindness) – more than a century of research and control. Acta Tropica. 2021;218:105677. doi:10.1016/j.actatropica.2020.105677. http://www.sciencedirect.com/science/article/pii/S0001706X20309918



Learn more about some Neglected Tropical Diseases in Africa below.




Published: June 2, 2023

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