River Blindness or Onchocerciasis is a parasitic disease transmitted by the bite of small black flies (blackflies of the species Simulium damnosum) that breed in rapidly flowing streams and rivers; hence the common name "river blindness." River blindness disease is a major cause of preventable blindness. The World Health Organization estimated 17.7 million are infected, 500,000 are visually impaired, and another 270,000 are blind due to the disease in 37 endemic countries. Approximately 123 million people live in endemic areas worldwide and are therefore at risk of infection; more than 99 percent of those infected reside in Africa, and Nigeria is the most endemic country in the world.
A parasite, by definition is an organism that lives in or on the living tissue of a host organism at the expense of that host. The biological interaction between the host and the parasite is called parasitism. Parasitism (by one definition) is a symbiotic relationship because both the parasite and host benefit. The relationship is said to be strictly parasitic if the host does not benefit from it.
Adult worms live in nodules in a human body where the female worms produce high numbers of first-stage larvae known as microfilariae. They migrate from the nodules to the sub-epidermal layer of the skin where they can be ingested by blackflies. They further develop in the body of the insect from which more people can be infected. Eye lesions in humans are caused by microfilariae. They can be found in all internal tissues of the eye -- except the lens -- where they cause eye inflammation, bleeding, and other complications that ultimately lead to blindness. The microfilariae also affect the lymphatic system. When the lymphatic system is involved the disease is called elephantiasis
Onchocerciasis is a major cause of blindness in many African countries. As a public health problem, the disease is most closely associated with West and Central Africa, but it is also prevalent in Yemen and six countries in Latin America. Onchocerciasis has in the past greatly reduced the economic productivity in infected areas and left vast tracts of arable land abandoned. It is estimated that there are about half a million blind people due to river blindness.
Initially, in coffee-producing countries like Guatemala and Mexico, contracting onchocerciasis was considered an occupational hazard for coffee harvesters because their work often brought them near the fast-flowing streams where the black flies breed. In Ethiopia, almost everyone in an endemic village will harbour the disease, because the black fly lives in most of the region.
Clinical Presentation. Infection with O. volvulus will result in a highly pruritic, papular dermatitis; subcutaneous nodules; lymphadenitis; and ocular lesions, which will most likely progress to visual loss and blindness. Symptoms in travellers are almost always dermatologic and may occur months to years after departure from endemic areas. Immigrants from endemic areas may present with skin and/or ocular disease. Diagnosis is made by finding the microfilariae in superficial skin shavings, adult worms in histologic sections of excised nodules, or characteristic eye lesions. Serologic tests may be done at research facilities.
Prevention and treatment. When it was first discovered that the disease was caused by the microfilariae the treatment of choice was the use of larvicides in streams and river beds to kill the fly larvae. This controlled the black fly populations and consequent reduced the spread of the disease. The process was expensive, environmentally risky, and difficult to implement.
The only medicines available had serious toxicities and could only be administered intravenously.
In the 1980s, the pharmaceutical company Merck & Co., Inc., demonstrated that annual treatment with the orally administered microfilaricidal drug, ivermectin , could not only help relieve the unpleasant symptoms from the skin disease but could also improve vision and prevent blindness. In 1987, Merck announced that it would donate ivermectin, to all who needed it, for as long as needed. What a noble action. The author of this article has no connections with Merck, is not their employee and does not hold any Merck shares.
The anthelmintic agent ivermectin, given in a single oral dose, is also an effective treatment for scabies in otherwise healthy patients and in many patients with HIV infection.
In 1987, The Carter Center became involved in the struggle to control and eliminate onchocerciasis by becoming an advocate for the ivermectin Donation Program launched by Merck. To-day The Carter Center is one of the only nongovernmental organizations combating river blindness in both Africa and the Americas. Since its inception, the Carter Center's River Blindness Program has assisted ministries of health in 11 countries to administer more than 76 million treatments. Writer of this article is not affiliated with the Carter Centre.
The usual standard dose of ivermectin is 150-200 µg/kg orally once or twice per year.
In 1992, the Onchocerciasis Elimination Program in the Americas (OEPA) was launched in 6 countries. Ivermectin distribution has been the main intervention strategy and the programme is now in the process of preparing for certification of the elimination of onchocerciasis in those countries
According to the WHO (2006 report), the onchocerciasis control programme of west Africa has saved 100000 people at immediate risk of contracting the disease and prevented the potential infection of nearly 12 million children. In addition, 1.25 million people have lost their onchocercal infection through the programme.
It is fortunate that free treatment is now available because this disease affects the poorest of the poor living in worlds poorest and economically deprived countries.
Well done, Nurse.