African People with River Blindness (Onchocerciasis)
River Blindness

The Visible But Still Unseen Disease

African woman with River Blindness
Credit: Neil Brandvold/DNDi

Onchocerciasis is an infection caused by the parasitic roundworm Onchocerca volvulus, spread by the bite of an infected blackfly of the genus Simulium. This neglected tropical disease is also called River Blindness because the vector that transmits infection breeds in rapidly flowing streams and the infection can cause blindness. Symptoms range from disfiguring skin damage to complete loss of vision. WHO estimates there are at least 20.9 million people infected with onchocerciasis. The majority of these cases (99%) are people living in tropical conditions in 31 African countries, but the disease also occurs in Latin America and Yemen.



Three African women with River Blindness
Credit: Neil Brandvold/DNDi

< In addition to the 20.9 million people infected with onchocerciasis, 23 million people live in areas that put them at risk of infection. Such areas are remote villages located on fertile land, adjacent to streams and rivers. This type of environment provides ideal breeding conditions for the blackflies which transmit the parasite responsible for the disease.


As its alternate name suggests, River Blindness is a disease that can cause eye inflammations, which ultimately result in lesions. Initially, and with sufficient treatment, these lesions are reversible. But without such treatment, the lesions lead to a clouded cornea and ultimately, blindness. Compared to healthy persons of the same age living in the same community, those made blind from this disease have a four times higher mortality rate. >

african man with river blindness
Credit: Neil Brandvold/DNDi

Skin problems caused by microfilariae
Credit: Neil Brandvold/DNDi
After a human is bitten by an infected blackfly, the parasite’s larvae migrate through the human host’s subcutaneous tissue. The larvae develop into the adult stage, and female worms give birth to microfilariae, the infective stage for the Simulium fly vector. When these microfilariae die, they can cause intense inflammation and severe skin problems. In 2017, 14.6 million people globally were afflicted with related skin damage because of the infection. Other effects of onchocerciasis are changes in skin color and loss of the skin’s elastic tissue, leading to severe "leathering" and thickening of skin. The disease can also contribute to debilitating skin conditions such as “hanging groin.” 


“Available treatment for River Blindness given via mass
medicinal administration reduces the number 
of larvae in the patient’s body. This prevents the long-term skin
damages and blindness.  However, the adult worms survive
and reproduce further after only a few months.
This requires that treatment is given every six to twelve months
for the entire life span of the adult worm.
And this can be up to twelve years.“

Dr. Maria-Luisa Rodriguez
Global Program Head with Pharmaceuticals at Bayer


 Doctor looking for river blindness symptoms
Credit: Neil Brandvold/DNDi
Diagnosing onchocerciasis can be difficult. Not all infected persons show symptoms because the parasite requires up to one year to become an adult and reproduce. And because it is the worms’ larvae that cause most symptoms, most infected people are asymptomatic, feeling well until after the adult worms start producing larvae. The adult worms can live up to 15 years in the human body, and female worms produce thousands of microfilariae daily. Skin biopsies and blood tests are used to diagnose the disease. Biopsies, however, are not always reliable. Currently, there is no vaccine or adulticidal treatment available. Therefore, microfilaricidal treatments need to be performed over the whole lifespan of the adult worms.

River Blindness can cause a lot of different symptoms
Credit: Neil Brandvold/DNDi
^ In addition to physical symptoms, the disease affects several areas of infected persons' social and economic lives. The huge burden caused by symptoms, such as itching skin and blindness, hinder many people from working. Not only are the entire families of sufferers at risk of poverty – whole communities are affected if too many people are infected and stop producing food or doing other economic activities. Consequently, onchocerciasis, which predominantly affects poor people in remote areas, can be directly linked to poverty. The damage from this disease also needs to be considered in terms of emotional pain, since infected people fear stigmatization. 

"The cooperation of Bayer with DNDi
on the development of emodepside for
the benefit of human health is another
great example of One Health.
Emodepside is an anthelmintic that
is already authorized for the treatment
of cats and dogs with worm infection.
The burden of the disease River Blindness
is enormous and we now hope that humans
can benefit from this innovation
  originating from veterinary medicine.”

Dr. Daniel Kulke
Parasitologist with Animal Health at Bayer



girl by river
Credit: Neil Brandvold/DNDi

< The disease’s stigmatization especially affects girls and young women. Their risk of leaving school increases if someone leading their household is infected. Infected women are limited in their choice of partners. The severe itching caused by the disease may also reduce the period that nursing mothers can breastfeed. For anyone affected, the itching can lead to insomnia. According to one sufferer in Uganda, suicide is sometimes seen as preferable to living with this disease.



Onchocerciasis is also a vast economic burden. The treatment goal for onchocerciasis has shifted from control to elimination in Africa. The elimination of this disease would reduce the need for health workers and outpatient services, and it would save up to 1.25 million USD annually for affected nations. This would result in substantial health and economic benefits for currently affected African countries. >

Credit: Neil Brandvold/DNDi


“A new treatment option for River Blindness
is urgently needed. 
Our compound emodepside
could be a novel option to treat this disease.
Together with DNDi (Drugs for Neglected Diseases initiative),
our focus is to develop a new oral,
short-course macrofilaricide treatment.“

Dr. Joerg Moeller
Global Head of R&D with Pharmaceuticals at Bayer



[1] WHO, Onchocerciasis

[2] NCBI, Chapter 15, Onchocerciasis

[3] CNN health

Related Content

People & Perspectives
“It’s a Silent Epidemic”
Read more
Read more
Prevention & Cures
Improving Information and Finding Cures
Read more
Prevention & Cures
On a Journey to Bandundu
Read more