Filaria – river blindness
Symptoms, transmission, and current treatments for filarial diseases
What are filarial diseases?
Filarial diseases are caused by parasitic worms that are transmitted by the bite of blood-feeding insects. This debilitating group of diseases includes river blindness and lymphatic filariasis (commonly known as elephantiasis).
What is river blindness?
Onchocerciasis, commonly known as river blindness, is a filarial disease caused by the parasitic nematode worm Onchocerca volvulus. People are infected by worms transmitted by the bite of blood-sucking blackflies, which breed in fast-flowing rivers.
River blindness is not usually fatal, but it inflicts hardship and misery on millions of people. In the human body, the adult worms produce embryonic larvae (microfilariae) that migrate to the skin, eyes and other organs. The worms can cause severe itching, disfiguring skin conditions, and blindness or impaired vision.
Efforts to eliminate river blindness are hampered in some areas by another parasitic infection known as Loiasis, or ‘African eye worm’. Individuals with a very high amount of Loa loa larvae (microfilariae) in the blood are at risk of life-threatening complications if they receive ivermectin, a drug for river blindness.
What is the impact of river blindness?
- 217.5 million people at risk
- 19 million people infected with river blindness
- 1.15 million people with vision loss
- 99% of people infected live in 31 African countries, predominantly in West and Central Africa
- 14.6 million people suffer from filarial skin diseases
What are current treatments for river blindness?
Current treatment for river blindness is based on repeated mass drug administration (MDA) of ivermectin to everyone living in an affected area. These efforts are directed by the country’s national control programmes and supported by international organisations, such as the World Health Organization (WHO), ESPEN, and the Task Force for Global Health. The drugs kill juvenile worms and temporarily sterilize adult worms. The adult worms remain alive in the body, eventually producing new offspring, often before the next MDA takes place. As a result, MDA must be repeated for many years.
Ivermectin is safe and has been used widely, however it:
- Requires many years of repeatedly taking the drug to reduce disease burden and eventually achieve elimination
- Cannot be used in areas where people also are burdened with high levels of juvenile Loa loa worms, because it can result in safety issues that can be fatal
- Only partly improves or prevents river blindness symptoms such as itching, dermatitis, and blindness because people continue to be affected by the adult worms living in their bodies
What new treatments for river blindness are needed?
WHO has targeted the elimination of river blindness in Latin America, in some African countries, and in Yemen by 2020. Countries are making steady progress, but it is likely that many elimination programmes will need to continue after 2025.
There is an unmet medical need for a drug that can kill the adult worms for use in the elimination effort and ideally in people who are also infected with Loa loa.
What river blindness treatments are we working on?
We aim to deliver a safe, effective, affordable, and field-adapted drug that can kill adult filarial worms (a ‘macrofilaricide’) and be used for prevention or individual treatment.
Find out about our work developing treatments for river blindness.
How do you get river blindness?
- Insect bites: river blindness is transmitted through the bite of a blackfly infected with Onchocerca volvulus worms
What are the symptoms of river blindness?
River blindness is not particularly life-threatening, but it causes long-term suffering and chronic illness:
- visual impairment and blindness
- severe itching
- nodules under the skin (around adult worms)
How is river blindness diagnosed?
- River blindness is diagnosed by identifying juvenile worms in skin snips.
- In patients with nodules in the skin, the nodule can be surgically removed and examined for adult worms.
- Infections in the eye can be diagnosed with a slit-lamp examination of the front part of the eye where the larvae or the lesions they cause are visible.
Antibody tests are available but cannot tell the difference between past and current infections, so they are not as useful in areas where river blindness is commonly found.
Accurate diagnosis of Loa loa coinfection is important when considering treatment with ivermectin, since rapid killing of large numbers of juvenile loa loa worms can cause serious side effects.
Last updated: April 2021
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