Onchocerciasis is an infection caused by the parasitic worm Onchocerca volvulus, spread by the bite of an infected Simulium blackfly.
It is also called River Blindness because the fly that transmits infection breeds in rapidly flowing streams and the infection can cause blindness.
Please find more information on this disease in the text below or watch expert interview:
What is the disease?
How dangerous is Onchocerciasis?
Worldwide onchocerciasis is second only to trachoma as an infectious cause of blindness and can cause debilitating and disfiguring skin disease.
Who is at risk?
The people most at risk for acquiring onchocerciasis are those who live near rivers where there are Simulium blackflies which are mostly found in rural agricultural areas in sub-Saharan Africa.
Usually, many bites are needed before being infected.
People who travel for periods of less than three months to areas where the parasite is found have a low chance of becoming infected with O. volvulus.
How many people are affected by Onchocerciasis?
The World Health Organization's (WHO) expert committee on onchocerciasis estimates that at least 25 million people are infected and 123 million people live in areas that put them at risk of infection.
About 300,000 people are blind because of the parasite and another 800,000 have visual impairment.
Where is Onchocerciasis found?
Onchocercal infections mainly occur in tropical areas. More than 99% of infected people live in 31 countries in sub-Saharan Africa: Angola, Benin, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Republic of Congo, Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Ethiopia, Gabon, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Malawi, Mali, Mozambique, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, South Sudan, Sudan, Togo, Uganda, United Republic of Tanzania.
The disease is also transmitted in Yemen in the Middle East, in one focal area in Venezuela and one in Brazil.
How do people get Onchocerciasis?
Onchocerciasis is transmitted to humans through exposure to repeated bites of infected blackflies of the genus Simulium.
What are the signs and symptoms of Onchocerciasis?
Onchocerciasis is an eye and skin disease. Symptoms are caused by the microfilariae, which move around the human body in the subcutaneous tissue and induce intense inflammatory responses when they die.
Some infected persons may be without symptoms.
Those with symptoms will usually have one or more of the three manifestations:
- skin rash, usually itchy
- eye disease
- nodules under the skin
The most serious manifestation consists of lesions in the eye that can lead to visual impairment and blindness.
How is the disease developing?
It can take up to one year for the larvae also called microfilariae to develop into an adult inside the human body and between 10 and 20 months before larvae can be found in the skin.
Each adult female worm, which can live from 10–15 years, can produce millions of new larvae during her lifetime.
As it is the larvae that cause most of the symptoms of onchocerciasis, most people feel well until after the adults start producing larvae.
More in-depth information:
The inflammation caused in the skin, in addition to causing itching, can result in long-term damage to the skin. This can cause changes in the color of the skin that result in a "leopard skin" appearance, and can cause thinning of the skin with loss of elastic tissue that gives the skin a "cigarette-paper" appearance and can contribute to conditions such as "hanging groin."
The inflammation caused by larvae that die in the eye may result initially in reversible lesions on the cornea that without treatment progress to permanent clouding of the cornea, resulting in blindness. There can also be inflammation of the optic nerve resulting in vision loss, particularly peripheral vision, and eventually blindness.
How is Onchocerciasis diagnosed?
Onchocerciasis is diagnosed by skin biopsies called „snips" or blood tests looking for antibodies to the parasite.
Examination of skin snips does not always show the parasites and positive blood tests do not necessarily indicate that someone is still infected with O. volvulus.
How is Onchocerciasis treated?
Infected and non-infected people infected with O. volvulus are treated with ivermectin as mass drug application in order to prevent the long-term skin damage and blindness.
The medicine will be given every six to 12 months for the life span of the adult worms or for as long as the infected person has evidence of skin or eye infection.
Ivermectin kills the larvae and prevents them from causing damage until new larvae are produced as it does not kill the adult worms.
How can I prevent infection?
There is neither a vaccine nor recommended drug available to prevent onchocerciasis.
As blackflies bite during the day the best prevention is to avoid being bitten by infected blackflies, using insecticides that contain N,N-Diethyl-meta-toluamide (DEET), wearing long sleeve shirts and pants, and wearing permethrin treated clothing.
How is Onchocerciasis transmitted?
The disease spreads by the bite of an infectious blackfly. When a blackfly bites a person whith onchocerciasis,
microscopic worm larvae called microfilariae in the infected person's skin enter and infect the blackfly.
The larvae develop over two weeks in the fly to a stage that is infectious to humans.
More in-depth information:
Humans become infected when blackflies deposit Onchocerca infective larvae into the skin when biting to extract blood. Once inside the human body, the larvae mature into adults in around three months to one year.
Most adult female worms live in fibrous nodules under the skin and sometimes near muscles and joints. Adult male worms are usually found near the female worms.
Nodules form around the worms as part of the interaction between the parasite and its human host. Inside the nodules the worms are relatively safe from the human immune response.
Adult female worms produce thousands of new larvae daily. The larvae become detectable in the skin ten to 20 months after the initial infection. The adult worms can live up to 15 years inside the human body, and their larvae have a lifespan up to two years.
What exactly does the vector do?
Blackflies breed along fast- flowing rivers close to villages whose inhabitants are engaged in agriculture.
An infectious blackfly will drop larvae when biting a person. The larvae then penetrate the skin and infect the person. Because the worms reproduce only in humans but need to complete some of their development inside the blackfly, the intensity of human infection, which means the number of worms in that person, is related to the number of infectious bites sustained.
How can the vector be controlled?
Between 1974 and 2002, disease caused by onchocerciasis was brought under control in West Africa through the work of the Onchocerciasis Control Programme (OCP), using mainly the spraying of insecticides against blackfly larvae by helicopters and airplanes.
- The Expanded Special Project for Elimination of Neglected Tropical Diseases (ESPEN) is a five year project which was launched by the World Health Organization’s (WHO) Regional Office for Africa (AFRO) in May 2016 to provide national NTD programmes with technical and fundraising support to help them accelerate the control and elimination of the five Neglected Tropical Diseases amenable to Preventive Chemotherapy (PC-NTDs) with the greatest burden on the continent, namely Onchocerciasis, Lymphatic Filariasis, Schistosomiasis, Soil Transmitted Helminthes and Trachoma, which collectively affect hundreds of millions of people.
- ESPEN will contribute to ensuring that national NTD programmes have the data, expertise and financial resources they need to accelerate the fight against these diseases by coordinating Partners and providing technical support. ESPEN was established following the closure of the African Programme for Onchocerciasis Control (APOC), which during its 20-year mandate made a major contribution to the reduction in onchocerciasis (river blindness) in Africa. ESPEN will maintain the gains made over the past two decades by integrating this approach across the five PC-NTDs.
What are the difficulties and challenges in fighting Onchocerciasis?
- maintaining and consolidating advances made in disease control
- enhancing access to diagnosis and treatment infected people
- increasing awareness of the disease among both the vulnerable population and all decision-makers who have an impact on the elimination of the disease
What programs exist against Onchocerciasis?
The worldwide burden of onchocerciasis has been considerably reduced as the result of very successful disease control programs led by the World Health Organization (WHO). These programs are based on control of the blackfly population and/or mass administration to affected communities of an oral drug called ivermectin (MectizanTM), that is donated by Merck & Co., Inc.
As a result of these programs, millions of people are at greatly reduced risk of debilitating itching, disfigurement, and blindness caused by onchocerciasis.
WHO headquarters provides administrative, technical and operational research support to three regions where onchocerciasis is transmitted.
The WHO Regional Office for Africa, which had an overall supervisory role for OCP from 1975 to 2002 and APOC from 1995 to 2015, currently supervises ESPEN which coordinates NTD control and elimination activities in that region.
Through the OEPA partnership, WHO collaborates with endemic countries and international partners in the WHO Region of the Americas. Although there is no official program to coordinate activities in the WHO Eastern Mediterranean Region, the two countries in the region collaborate on elimination activities.
More in-depth information:
Between 1974 and 2002, disease caused by onchocerciasis was brought under control in West Africa through the work of the Onchocerciasis Control Programme (OCP), using mainly the spraying of insecticides against blackfly larvae (vector control) by helicopters and airplanes.
This has been supplemented by large-scale distribution of ivermectin since 1989.
The OCP relieved 40 million people from infection, prevented blindness in 600 000 people, and ensured that 18 million children were born free from the threat of the disease and blindness.
In addition, 25 million hectares of abandoned arable land were reclaimed for settlement and agricultural production, capable of feeding 17 million people annually.
The African Programme for Onchocerciasis Control (APOC) was launched in 1995 with the objective of controlling onchocerciasis in the remaining endemic countries in Africa and closed at the end of 2015 after beginning the transition to onchocerciasis elimination.
Its main strategy has been the establishment of sustainable community-directed treatment with ivermectin (CDTI) and vector control with environmentally- safe methods where appropriate.
In APOC’s final year, more than 119 million people were treated with ivermectin, and many countries had greatly decreased the morbidity associated with onchocerciasis. More than 800,000 people in Uganda and 120,000 people in Sudan no longer required ivermectin by the time that APOC closed.
In 2016, more than 129 million people were treated in Africa where the strategy of CDTI was implemented, representing approximately 65.3% coverage of the number of people who require treatment globally.
The Expanded Special Project for the Elimination of Neglected Tropical Diseases in Africa (ESPEN), which has replaced APOC, will initially focus on several priority countries to support their neglected tropical diseases (NTDs) programs, including their onchocerciasis programs, and will create a pool of experts that can provide technical assistance to all member countries. ESPEN, like OCP and APOC, is housed in the WHO Regional Office for Africa.
The Onchocerciasis Elimination Program of the Americas (OEPA) began in 1992 with the objective of eliminating ocular morbidity and interruption of transmission throughout the Americas by 2015 through biannual large- scale treatment with ivermectin. All 13 foci in this region achieved coverage of more than 85% in 2006, and transmission was interrupted in 11 of the 13 foci so far in 2017. Elimination efforts are now focused on the Yanomami people living in Brazil and Venezuela.
On 5 April 2013, the Director-General of WHO issued an official letter confirming that Colombia has achieved elimination of onchocerciasis. Colombia was the first country in the world to be verified and declared free of onchocerciasis by WHO.
This has been followed by Ecuador in September 2014, Mexico in July 2015, and Guatemala in July 2016. More than 500 000 people no longer need ivermectin in the Americas.
The Expanded Special Project for Elimination of Neglected Tropical Diseases (ESPEN) is a five year project which was launched by the World Health Organization’s (WHO) Regional Office for Africa (AFRO) in May 2016 to provide national NTD programmes with technical and fundraising support to help them accelerate the control and elimination of the five Neglected Tropical Diseases amenable to Preventive Chemotherapy (PC-NTDs) with the greatest burden on the continent, namely Onchocerciasis, Lymphatic Filariasis, Schistosomiasis, Soil Transmitted Helminthes and Trachoma, which collectively affect hundreds of millions of people.
ESPEN will contribute to ensuring that national NTD programmes have the data, expertise and financial resources they need to accelerate the fight against these diseases by coordinating Partners and providing technical support. ESPEN was established following the closure of the African Programme for Onchocerciasis Control (APOC), which during its 20-year mandate made a major contribution to the reduction in onchocerciasis (river blindness) in Africa. ESPEN will maintain the gains made over the past two decades by integrating this approach across the five PC-NTDs.
What does Bayer contribute to the fight against Onchocerciasis?
Bayer has signed in 2014 an collaboration agreement with DNDi (Drugs for Neglected Diseases initiative) –– to develop together a new treatment option for river blindness.
Drugs for Neglected Diseases initiative (DNDi) is a collaborative, patients’ needs-driven, non-profit drug research and development (R&D) organization that is developing new treatments for neglected diseases.
DNDi aims to deliver:
- a new oral, short-course macrofilaricide treatment, with potential application to treat onchocerciasis
- The currently available drugs against river blindness are only effective against the parasites' microfilariae, i.e. larvae and young worms. However, the adult worms survive until the end of their natural lifespan and produce more and more new generations of offspring. Thus the drugs have to be given as MDA for up to 15 years.
The compound emodepside, by contrast, is a macrofilaricide which also kills the adult nematodes. The active substance has already proved its worth in veterinary medicine. Bayer's Animal Health Division has been offering the antiparasitic agent since 2005 in various combinations of active ingredients for combating worms in domestic animals.
Emodepside originates from the Japanese pharmaceutical company Astellas and has been developed by Bayer’s Animal Health division for veterinary use. Preclinical studies have shown that the active substance effectively kills the nematodes responsible for river blindness. Astellas has granted Bayer the rights to develop emodepside along these lines.
This could significantly shorten the duration of treatment, which would mean significant progress in the long-term fight against river blindness. A shorter treatment period would reduce the pressure not only on the affected patients, but also on the local healthcare systems. The drug would be suitable not only for mass treatment, but also for individual therapy.
What is the societal burden of Onchocerciasis?
Onchocerciasis is a serious threat to public health and an impediment to socio-economic development in areas with high intensity and high endemicity of the disease. In such places, blindness and serious visual impairment are common, and mortality among the blind may be four times as high as among non-blind persons of the same age in the same community.
As a result of debilitation and blindness, the infected person is unable to maintain for long any type of productive activity.
Additionally, to avoid infection and its consequences many young men migrate to urban areas, reducing the productivity of the community and disrupting family life.
Employees cassified as having a severe Onchocercal Skin Disease (OSD) earned 15 % less in daily wages than those not infected.
People with Onchocercal Skin Disease are stigmatized in their communities. OSD limits the range of social involvement and can affect sexual life of affected individuals. With reference to women and children, young females with OSD suffer stigmatization more than young men. This affects their age of marriage and the kind of partners they marry, limiting them to already married men, divorced men, elderly men, childless men, etc.
Severe itching that often accompanies OSD may reduce the period lactating mothers breastfeed their babies.
Children, particularly females, from households headed by individuals with onchocerciasis, especially blindness and OSD are more at risk of being school dropouts. Academic performance of school children with visual impairment is adversely affected.
What are the economic effects of the elimination of Onchocerciasis?
The treatment goal for onchocerciasis has shifted from control to elimination in Africa. For investment decisions, national and global policymakers need evidence on benefits, costs and risks of elimination initiatives.
The elimination of onchocerciasis in Africa would avert 4.3 million–5.6 million disability-adjusted life years over 2013–2045 when compared with staying in the control mode, and also reduce the required number of community volunteers by 45–53% and community health workers by 56–60%.
The elimination of onchocerciasis in Africa when compared with the control mode is predicted to save outpatient service costs by $37.2 million–$39.9 million and out-of-pocket payments by $25.5 million–$26.9 million over 2013–2045, and generate economic benefits up to $5.9 billion–$6.4 billion in terms of income gains.
The elimination of onchocerciasis in Africa would lead to substantial health and economic benefits, reducing the needs for health workforce and outpatient services. To realize these benefits, the support and collaboration of community, national and global policymakers would be needed to sustain the elimination strategies.
How did the history of the disease proceed?
- In 1874 the microfilarial parasite that causes the disease was first identified by Irish naval surgeon John O’Neill, who was seeking to identify the cause of a common skin disease along the west coast of Africa, known as “craw-craw”.
- In 1890 the German zoologist, Rudolf Leuckart examined specimens of the same filarial worm sent from Africa by a German missionary doctor and named the organism Filaria volvulus.
- In 1915 Rodolfo Robles and Rafael Pacheco in Guatemala first mentioned the ocular form of the disease in the Americas. The disease, commonly called the “filarial blinding disease”, and later referred to as “Robles disease”, was common among coffee plantation workers. Manifestations included subcutaneous nodules, anterior eye lesions, and dermatitis.
- In 1919 Robles sent specimens to Émile Brumpt, a French parasitologist, who named it O. caecutiens, indicating the parasite caused blindness (Latin “caecus” meaning blind).
- By the early 1920s, it was generally agreed that the filaria in Africa and Central America were morphologically indistinguishable and the same as that described by O’Neill 50 years earlier.
Robles hypothesized that the vector of the disease was the day-biting black fly, Simulium. Scottish physician Donald Blacklock of the Liverpool School of Tropical Medicine confirmed this mode of transmission in studies in Sierra Leone. Blacklock’s experiments included the re-infection of Simulium flies exposed to portions of the skin of infected subjects on which nodules were present, which led to elucidation of the life cycle of the Onchocerca parasite.
In 1930 the Belgian ophthalmologist Jean Hissette discovered that the organism was the cause of a “river blindness” in the Belgian Congo. Some of the patients reported seeing tangled threads or worms in their vision, which were microfilariae moving freely in the aqueous humor of the anterior chamber of the eye.
Blacklock and Strong had thought the African worm did not affect the eyes, but Hissette reported that 50% of patients with onchocerciasis near the Sankuru river in the Belgian Congo had eye disease and 20% were blind.
- In 1945 ophthalmologist Harold Ridley, who also made extensive observations on onchocerciasis patients in north west Ghana, published his findings followed by Hisette, who had isolated the microfilariae from an enucleated eye and described the typical chorioretinal scarring, later called the “Hissette-Ridley fundus”.
Ridley first postulated that the disease was brought by the slave trade. The international scientific community was initially skeptical, but Hisette’s findings were confirmed by the Harvard African Expedition of 1934, led by Richard P. Strong, an American physician of tropical medicine.