By Adaobi Rhema Oguejiofor
Over the years, onchocerciasis, also known as river blindness, a parasitic disease transmitted by infected black flies has remained a major public health concern in Nigeria, significantly impacting communities, particularly in rural areas. According to the United States Agency for International Development (USAID) Act to End Neglected Tropical Diseases (NTDs) program, Nigeria is home to the largest population at risk for river blindness globally, with over 100 million people in 32 states and the Federal Capital Territory affected. This finding makes the nation the global epicentre of the disease. Despite this, Nigeria has made remarkable progress in the worldwide effort to tackle and eliminate the river blindness disease.
Onchocerciasis, caused by the onchocerca volvulus worm transmitted to humans through the bites of infected black flies, causes severe visual impairment and can lead to actual blindness. It remains one of the leading causes of preventable blindness in the world, primarily affecting rural populations in sub-Saharan Africa, with small numbers of cases in Latin America and Yemen.
The Disease and Its Transmission
Onchocerciasis is transmitted through the bite of infected blackflies (Simulium species), which breed in fast-flowing rivers and streams. The blackfly vector ingests microfilariae (immature worms) when it bites an infected person. Inside the fly, the micro-filariae develop into infective larvae that are then transmitted to another human during subsequent bites. When the blackfly bites a person it injects larvae into the skin, which matures into adult worms, forming nodules under the skin. These adult worms can live for up to 15 years in the human body, during which the female worms can release millions of microfilariae migrating into the bloodstream, skin, and eyes, causing intense itching, and severe damage, including blindness.
The World Health Organization (WHO) revealed that the most devastating consequence of onchocerciasis is on the eyes. When microfilariae migrate to the eyes, they can trigger an immune response, leading to the ocular tissues’ inflammation and damage. Over time, this can result in vision impairment and eventually blindness. It is estimated that onchocerciasis is the second leading infectious cause of blindness worldwide, after trachoma. It is responsible for more than 99% of cases of blindness caused by parasitic infection. However, the disease’s impact is not only physical but also social and economic, as individuals with river blindness may face both stigmatisation and limited opportunities due to their disability.
Symptoms and Health Consequences
The symptoms of onchocerciasis differ depending on the stage of the infection and the organs involved:
– Skin Symptoms:
The most common symptom of the disease on the skin is intense itching, which can lead to skin damage over time. This skin damage comes in the form of skin thickening and discolouration known as “leopard skin”. The skin can become wrinkled, rough, and infected, causing disfigurement. Chronic inflammation can also cause atrophy, resulting in lizard skin-like changes.
– Eye Symptoms:
When it comes to the eyes, the migration of microfilariae to the eyes can cause inflammation and lesions, ultimately leading to blindness if untreated. River blindness is one of the most debilitating forms of blindness. This is because it often affects individuals in their productive years, severely limiting their quality of life.
– Nodules:
Adult worms form subcutaneous nodules that can be felt under the skin. These are generally not painful but are visible and can be very disturbing.
In the long run, river blindness can have significant impacts on its victims like impairing their ability to work and perform daily activities. This, in turn, leads to loss of income and increased dependence on others, perpetuating cycles of poverty in affected communities. The stigma associated with the visible manifestations of the disease also contributes to social exclusion. Also, early exposure to onchocerciasis in childhood has been associated with epilepsy, known as onchocerciasis-associated epilepsy.
Efforts have been ongoing to eliminate the disease and its impact on communities. Thanks to large-scale public health interventions, including the mass distribution of ivermectin and increased community awareness, Nigeria has emerged as a global leader in the fight to eliminate the disease. These efforts have not only helped reduce the prevalence of river blindness but have also contributed to the country’s broader goal of eliminating neglected tropical diseases (NTDs) by 2030.
However, challenges remain, and continued investment, collaboration, and innovation are essential to completely eradicate this debilitating disease. In 2023, the Federal Government of Nigeria disclosed that it successfully achieved the criteria necessary to stop the treatment for river blindness in Imo, Abia, Enugu, and Anambra states, representing more than 18.9 million people.
The Federal Government explained that the states joined 10 others that had achieved intermittent transmission of river blindness, enabling Nigeria to stop treatment for more than 28 million people, more than any other country in the world. The chairperson of Nigeria’s Onchocerciasis Elimination Committee, Professor Bright Nwoke expressed how pleased that the nation, once again, served as a beacon of inspiration not only for river blindness elimination globally but also for all the countries around the world working to eliminate neglected tropical disease.
Prevention
The best way to prevent onchocerciasis is to avoid bites from blackflies. However, one can protect themselves by:
– Using the Environmental Protection Agency (EPA)-registered insect repellents containing N, N-diethyl-m-toluamide (DEET) or another EPA-registered active ingredient.
– Wear loose-fitting, long-sleeved shirts and trousers, especially during the day because that is when blackflies bite.
– People can be protected by keeping windows and doors closed or covered with screens to keep biting insects out.
Treatment
Although there is no vaccine or drug to prevent onchocerciasis infection, there are anti-parasitic drugs like ivermectin that can kill the immature worms (microfilariae). These drugs will help prevent symptoms of the disease from further developing. However, the medication will not kill adult worms or prevent them from reproducing. As a result, a person will need to take the medication every 6 months for 10 to 15 years, which is the potential lifespan of the parasite.
According to Medical News Today, there is also an off-label medication like doxycycline that has the ability to kill adult worms. Prescribing a drug off-label means using it in a way that differs from its approved use. This antibiotic essentially starves the worms to death by killing the bacteria they feed on.
There is a global campaign to eliminate onchocerciasis transmission in endemic areas. The campaign focuses on controlling blackflies and giving medicine that kills the microscopic worms to entire affected communities. Successful campaigns to eliminate onchocerciasis have taken place in some countries, including countries in the Western part of the world.
Concerns have also been raised about the long-term sustainability of ivermectin treatment, particularly as drug resistance in blackflies and parasites may develop over time. Continued research into vaccines and new therapeutic strategies is therefore critical to achieving the goal of global eradication.
The World Health Organization has set an ambitious goal of eliminating onchocerciasis as a public health problem by 2030. To achieve this, comprehensive strategies must continue, focusing on expanding access to treatment, improving surveillance systems, and increasing community awareness. The partnership between governments, international organisations, and local communities will be crucial in overcoming the remaining barriers.
As progress continues, the long-term vision for onchocerciasis is not just control but complete eradication, eliminating the disease’s devastating impact on the lives of millions and restoring sight to those who have lost it.