Onchocerciasis, also known as river blindness, is the world's second leading infectious cause of blindness. It is caused by ''Onchocerca volvulus,'' a nematode that can live for up to fifteen years in the human body though it can also live in other mammals. It is transmitted to humans through the bite of a black fly. The worms spread throughout the body, and when they die, they cause intense itching and a strong immune system response that can destroy nearby tissue, such as the eye.
Treatment may involve the use of the drug ivermectin. For best effect, entire communities are treated at the same time. A single dose may kill first-stage larvae (microfilariae) in infected people and prevents transmission for many months in the remaining population. Other drugs are also available. The removal of the palpable nodules is popular in Guatemala, Ecuador, and Mexico.
What Onchocerciasis may be divided into the following phases or types:
- Erisipela de la costa
- Mal morando
Additionally, the various skin changes associated with onchocerciasis may be described as follows:
Since 1988, ivermectin has been provided free of charge by Merck & Co. through the Mectizan Donation Program (MDP). The MDP works together with ministries of health and non-governmental development organisations such as the World Health Organization to provide free Mectizan to those who need it in endemic areas.
A study of 2501 people in Ghana showed that the prevalence rate doubled between 2000 and 2005 despite treatment, suggesting that the parasite is developing resistance to the drug. A clinical trial of another parasitic agent, moxidectin (manufactured by Wyeth), began on July 1, 2009 (NCT00790998).
99% of onchocerciasis cases occur in Africa. About 18 million people are currently infected with this parasite; approximately 300,000 have been permanently blinded. Onchocerciasis is currently endemic in 30 African countries, Yemen, and isolated regions of South America. Travelers who do not stay long in those areas have little risk of developing the disease as it requires prolonged exposure to the fly bites and parasite introduction.
Onchocerciasis is endemic in 36 countries across Africa, Latin America and Yemen. Over 85 million people live in endemic areas and half of these reside in Nigeria. Another 120 million people are at risk for contracting the disease. Due to the vector’s breeding habit, the disease is more severe along the major rivers in the northern and central areas of the continent, and severity declines in villages farther from rivers.
According to a 2002 WHO report, Onchocerciasis has not caused a single death, but its global burden is 987,000 Disability Adjusted Life Years (DALYs). The severe pruritis alone accounts for 60% of the DALYs. Infection reduces the host’s immunity and resistance to other diseases. This results in an estimated reduction in life expectancy of 13 years.
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Last Updated: Feb 1, 2011