River Blindness: Causes and Symptoms

Onchocerciasis, also called river blindness, is a skin and eye infection caused by the parasitic worm Onchocerca volvulus, which spreads through the bites of blackflies that breed near fast-flowing rivers. Many infected people have no symptoms, but others develop intense itching, rashes, lumps under the skin and, over time, vision loss, so anyone with possible exposure and these signs should be checked by a clinician.

In the United States, river blindness is rare. It is almost always seen in people who lived for a long time in, or came from, the places where it spreads. This page explains what the infection is, who is at risk, the symptoms, how it is diagnosed, and what treatment involves. It is general education, not a diagnosis.

What is river blindness?

The CDC describes onchocerciasis as a skin and eye disease caused by a microscopic parasitic worm. The World Health Organization (WHO) explains how it spreads:

1. A blackfly of the genus Simulium bites a person who is already infected and takes up tiny immature worms, called microfilariae, from their skin.
2. Inside the fly, the microfilariae develop into infective larvae.
3. When the fly bites someone else, the larvae enter the skin through the bite.
4. In the new host, the larvae grow into adult worms. The adults live in lumps (nodules) under the skin and release large numbers of new microfilariae, which move through the skin and can reach the eyes.

Most of the harm comes from the microfilariae. WHO notes that the body reacts strongly when they die, and that inflammation is what causes the itching, skin damage and eye damage.

Why is it called river blindness?

The name comes from two facts. WHO explains that the blackflies that spread the infection breed in rapidly flowing rivers, so the people who live or work near those rivers are the ones bitten again and again. Over years, the infection can damage the eyes and lead to visual impairment and, in some people, permanent blindness. River plus blindness gave the disease its common name, while onchocerciasis is its medical name, taken from the worm Onchocerca volvulus.

Who is at risk?

According to the CDC and WHO:

• More than 99% of infected people live in Africa, mostly in rural sub-Saharan Africa, and in Yemen. A small area on the border of Brazil and Venezuela makes up most of the rest.
• It takes repeated bites from infected blackflies to become infected. The CDC notes that, unlike malaria, river blindness rarely occurs in casual travelers.
• Travelers at higher risk are those who stay in affected areas for long periods, such as missionaries, Peace Corps volunteers and field researchers.

River blindness does not spread from person to person by touch, and it is not caught from someone's household. Several countries in the Americas, and Niger in Africa, have been verified by WHO as free of the disease after long elimination programs.

Symptoms of onchocerciasis

The CDC says many people infected with the worms never show symptoms. When symptoms do appear, the most common are:

• Intense itching, which can be severe and persistent
• Itchy skin rashes and other skin changes over time
• Lumps (nodules) under the skin, which form around the adult worms
• Eye problems, ranging from irritation and inflammation to vision loss and, in some people, permanent blindness

WHO adds that early exposure to the infection has been linked with epilepsy in children in affected regions. Symptoms can take a long time to develop, so someone may notice them months or years after leaving the area where they were exposed.

Itching and rashes have many common causes, including eczema, allergies, scabies and other skin conditions. These signs on their own do not mean river blindness. The combination of long stays in an affected region and skin or eye symptoms is what makes a clinician consider it.

How is onchocerciasis diagnosed?

Diagnosis needs a clinician, and usually a specialist in travel or tropical medicine. The CDC lists several ways to confirm it:

• Skin snip. A very thin skin sample is examined under a microscope for microfilariae. The CDC calls this the most common way to diagnose onchocerciasis.
• Nodule removal. A lump under the skin is surgically removed and checked for adult worms.
• Eye examination. An eye specialist looks for signs of damage, or for the microfilariae themselves.
• Blood test. A test can look for antibodies the immune system made in response to the infection.

Your clinician will also ask where you have lived and traveled, and for how long. This matters for another reason: some regions of West and Central Africa also have a different filarial worm, Loa loa, and the ivermectin prescribing information says people with significant exposure to those areas should be assessed for it before treatment (see below).

River blindness treatment

Treatment is with prescription antiparasitic medicine, chosen and supervised by a clinician. The prescribing information for the brand-name ivermectin tablet lists onchocerciasis as one of its two labeled uses; the other is intestinal strongyloidiasis. You can read more about the medicine in what is ivermectin and what is it used for.

What the labeling says about this use:

• Ivermectin acts against the microfilariae in the tissues, not the adult worms. Because the adult worms are not killed, the labeling says repeated follow-up and retreatment are usually required, on a schedule your clinician sets.
• Surgical removal of nodules may be considered as part of care, because it removes the adult worms that produce microfilariae.
• People treated for onchocerciasis may have a Mazzotti reaction in the first few days, which the labeling attributes to the body's response to dying microfilariae. Reported effects include itching, rash and skin swelling, fever, joint pain, and swollen or tender lymph nodes. Eye irritation and inflammation have also been reported. Your clinician will tell you what to watch for and when to call.
• Loa loa warning. Rarely, people with onchocerciasis who are also heavily infected with Loa loa have developed a serious, sometimes fatal brain reaction (encephalopathy) after treatment. That is why the labeling calls for assessment for Loa loa before treatment, and careful follow-up afterward, in anyone with significant exposure to Loa loa areas of West or Central Africa.

WHO uses ivermectin in community-wide treatment programs in affected countries. That is a public-health strategy for whole populations, and it is different from how an individual patient in the United States is assessed and treated. How much medicine, and how often, is always the prescriber's decision. We do not publish doses or schedules, and you should follow the directions on your own prescription label. General side effects and who should avoid ivermectin are covered in ivermectin side effects and who should not take these medications.

When to see a clinician in person

For suspected river blindness, an in-person visit is usually the right first step, because diagnosis relies on skin snips, an eye exam or nodule removal. See a clinician promptly, and ask about a travel or tropical medicine specialist, if you:

• Lived in or spent long periods in sub-Saharan Africa, Yemen or the Brazil–Venezuela border area, and have ongoing itching, rashes or lumps under the skin
• Notice any change in your vision, eye pain or eye redness
• Have spent significant time in West or Central Africa, where Loa loa also occurs

Seek urgent care for sudden vision changes, confusion, severe headache or any serious reaction after treatment.

Can I get ivermectin for river blindness online?

An online consultation cannot do a skin snip or an eye exam, so it is not a substitute for a specialist's diagnosis. If you already have a confirmed diagnosis and your own clinician's plan, a licensed provider can review your history through Get It Prescribed and decide whether ivermectin is appropriate. You complete a written health assessment and pay a one-time $50 consultation fee; the ivermectin tablet costs $3.00 per tablet, and the prescriber decides the quantity. The service is available in all 50 states and the District of Columbia, and some states require a live phone or video visit. The steps are laid out in ivermectin prescription online. How it works walks through each step.

A prescription is never guaranteed. The ivermectin dispensed through Get It Prescribed is a compounded preparation made by a licensed compounding pharmacy for an individual patient. Compounded preparations are not FDA-approved, and the FDA does not review them for safety, effectiveness or quality. They are not generics of, or substitutes for, the brand-name product.

An online review is not the right route if you have eye symptoms, have spent significant time in Loa loa areas of West or Central Africa without being assessed for it, are pregnant or breastfeeding, or feel seriously ill. See a clinician in person.

Related questions

Why is onchocerciasis called river blindness?

Because the blackflies that spread it breed in fast-flowing rivers, so people who live or work near those rivers are bitten again and again, and over years the infection can damage the eyes and cause vision loss or blindness. Onchocerciasis is the medical name, from the worm Onchocerca volvulus.

What is river blindness?

River blindness is the common name for onchocerciasis, an infection with the parasitic worm Onchocerca volvulus. It spreads through repeated bites from infected blackflies that breed near fast-flowing rivers, mostly in rural sub-Saharan Africa and Yemen. It affects the skin and eyes and, without care, can lead to vision loss.

What are the symptoms of onchocerciasis?

Many people have none. When symptoms appear, the most common are intense itching, itchy rashes, lumps under the skin and eye problems that can progress to vision loss. Symptoms can show up months or years after exposure. Because itching and rashes have many causes, a clinician needs tests to confirm it.

How is onchocerciasis treated?

With prescription antiparasitic medicine chosen by a clinician. Onchocerciasis is one of the two labeled uses for oral ivermectin. The labeling notes that ivermectin acts on the immature worms rather than the adult worms, so follow-up and retreatment are usually needed, and people with exposure to Loa loa areas should be assessed before treatment.

Can you get river blindness in the United States?

River blindness does not spread in the United States, and the CDC says it rarely affects casual travelers because it takes repeated blackfly bites. Cases seen in the US are almost always in people who lived in, or spent long periods in, affected parts of Africa, Yemen or South America.

How is river blindness diagnosed?

Most often with a skin snip, a very thin skin sample checked under a microscope for immature worms. A clinician may also remove a skin nodule to look for adult worms, examine the eyes, or order a blood antibody test. A travel or tropical medicine specialist usually leads the workup.

Sources

• CDC: About Onchocerciasis — symptoms, who is at risk, how it spreads, prevention and diagnosis.
• WHO: Onchocerciasis fact sheet — how blackflies transmit the parasite, where it occurs, clinical signs and elimination programs.
• MedlinePlus: Ivermectin — consumer drug information from the National Library of Medicine.
• DailyMed: ivermectin tablet prescribing information — labeled uses, the Mazzotti reaction and the Loa loa warning for onchocerciasis.
• FDA: Compounding and the FDA — Questions and Answers — what compounded preparations are and how they are regulated.