Onchocerciasis — commonly called river blindness — is a parasitic infection common in sub-Saharan Africa. It’s the second most common cause of infectious blindness globally.
The World Health Organization (WHO) regards onchocerciasis as one of the neglected tropical diseases — or NTDs. Though they affect more than one billion people all over the world, NTDs haven’t received widespread attention, mainly because most of the affected people are from the world's poorest countries. The WHO has set a goal of eliminating onchocerciasis from 12 such countries by 2030.
Read on to learn what you need to know about river blindness.
What Is River Blindness and What Causes It?
River blindness is caused by Onchocerca volvulus, a parasitic worm that spreads via black flies. Black flies are mainly found around rivers, and they feed on blood, so they bite humans and some animals.
When a black fly carrying Onchocerca larvae bites a person, the larvae enter their skin through the bite wounds. Usually, a black fly will have to bite you many times for the infection to take hold and cause onchocerciasis.
The larvae then grow and multiply inside small bumps on the skin to stay away from your immune system. In the next 12 to 18 months, these larvae mature into adults, migrate throughout the body, and live and reproduce there for over 10 years while feeding on various bodily fluids.
Onchocerciasis happens when Onchocerca larvae reach the eyes. Here the body's inflammatory response kills them. The dead larvae accumulate in the eye’s tissues and cause scarring. Also, the inflammatory response further damages the eyes. All of this eventually leads to visual impairment or even blindness.
The parasite also causes skin damage over time — which include skin discoloration and extreme itching.
What Are Onchocerciasis Symptoms?
People with river blindness may have no symptoms at all in the beginning. Because the symptoms are caused by dead larvae and the body’s immune response to them, they may take at least a year to start showing and worsen over time.
Onchocerciasis symptoms can be divided into skin and eye symptoms. Of them, the skin symptoms may appear many years before the eye symptoms — they include:
- Very itchy skin
- Dermatitis
- Raised bumps on the skin
- Leopard skin — pigment loss similar to vitiligo in some areas (often the shins)
- Lizard skin — dry, scaly skin similar to that seen in ichthyosis)
- Enlarged or hanging skin around the groin — sometimes with swollen lymph nodes
The disease can affect any or all parts of the eyes. The eye symptoms, which may start developing over 10 to 15 years after the black fly bite, include:
- Cataracts
- Ocular lesions — abnormal growths on the eyes
- Redness and irritation
- Light sensitivity
- Visual disturbances
In some extreme case, glaucoma, corneal damage, retinal damage may be seen.
Is River Blindness Permanent and How Does It Impact Life?
River blindness is a treatable infection, but it can cause permanent skin damage and blindness when left untreated for a long time. In some cases, eye surgery, such as glaucoma surgery or cataract surgery, can be needed to restore vision.
In some advanced cases — where the infection has damaged several parts of the eye — there's often no treatment available, and the resulting blindness is permanent.
People with river blindness usually have a poor quality of life. Even after treatment, people with river blindness may have shortened life expectancy because of onchocerciasis‐related epilepsy or compromised immunity. Vision problems can also make it difficult for the affected people to get enough food, leading to them developing malnutrition or starving. About 2% of those affected even consider suicide.
How Is River Blindness Diagnosed?
A doctor will diagnose river blindness with a skin snip — a biopsy in which a small amount of skin is removed using a biopsy punch or scalpel. The skin sample is then put into a saline solution — so that any larvae detach from the skin — and viewed under a microscope.
The doctor will take several biopsies to make sure that larvae are found if you’re infected and recommend antibody tests to confirm the diagnosis. They may also use a slit lamp eye exam to see larvae present in the eye or examine any eye lesions you may have.
How Is River Blindness Treated?
Ivermectin is the most commonly used to treat river blindness. It kills the larvae but not mature worms, so it needs to be taken every six months for the worm’s life span, which is 10 to 15 years. Doxycycline, which can kill adult worms, may be prescribed after ivermectin treatment is completed.
Moxidectin — a new drug approved for onchocerciasis treatment by the U.S. Food and Drug Administration in 2018 — has been found to be more effective than ivermectin in killing the larvae.
Additional medications are currently being studied for potential as a river blindness treatment, including the antibiotic TylAMac and the antiparasitic drug oxfendazole.
Where Am I More Likely to Get River Blindness?
Black flies are the most active where they breed, near fast-moving rivers and streams, so you should exercise caution in these areas.
More than 99% of river blindness cases have been reported in sub-Saharan Africa, where it’s the leading cause of blindness. Other places include Yemen and Latin America.
How Can I Prevent River Blindness?
Currently, there's no medication or vaccine that can prevent river blindness. So, the best way to prevent river blindness is to avoid high infection areas.
If you’re in a place where river blindness is common and want to prevent black fly bites, you should take the following steps:
- Use an effective insect repellant — like DEET
- Expose as little skin as possible — by wearing long sleeves and long pants and by tucking your pants into your boots
- Treat your clothes with permethrin — which is an insect repellent effective on fabric
- Avoid fast-moving rivers and streams during the day — when black flies are most likely to be active