Did you mean: onchocerciasis, river blindness (disease), Onchocerciasis (in medicine)
Dictionary:
on·cho·cer·ci·a·sis (ŏng'kō-sər-kī'ə-sĭs)  |
A disease caused by infestation with filarial worms of the genus Onchocerca, especially a disease of humans caused by O. volvulus and characterized by nodular swellings on the skin and lesions of the eyes. Transmitted by black flies, the disease occurs in tropical regions of Africa and Central America. Also called river blindness.
[New Latin : Onchocerca, genus name (Greek onkos, barb + Greek kerkos, tail) + –IASIS.]
| 5min Related Video: ONCHOCERCIASIS |
| Encyclopedia of Public Health: Onchocerciasis |
Onchocerciasis, or river blindness, is a filarial infection caused by the parasitic nematode, Onchocerca volvulus, carried by black flies of the genus Simulium. It is estimated that 17.7 million people are infected with O. volvulus, with 95 percent of those infected found in Africa. The infection is also found in areas of Central and South America and in the Arabian peninsula. Onchocerciasis is a significant cause of blindness in endemic countries. Of those people currently infected, approximately 270,000 are blind and a further 500,000 have severe visual impairment.
Simulium spp. are biting flies that are active during the day, breeding in fast flowing, well-oxygenated waters. Infection prevalence is highest in areas adjacent to such rivers, hence the term "river blindness." Transmission occurs when an infected fly takes a blood meal from a human and injects O. volvulus larvae (called microfilariae) into the host. The microfilariae develop into adult worms over the next one to two years. When mature, the adult worms produce new microfilariae that migrate throughout the skin of the host. A female adult worm may live for as long as ten years and will produce 1,300 to 1,900 microfilariae per day. These new microfilariae can be taken up by a biting fly, and thus the cycle of infection is completed.
Adult worms seldom cause any symptoms except as subcutaneous nodules around bony prominences. As microfilariae migrate throughout the body the following symptoms occur: severe itching, rashes, depigmentation of the skin, especially of the lower limbs ("leopard skin"); and destruction of skin elasticity, resulting in loose, hanging folds ("hanging groin"). The most devastating effect of onchocerciasis results when micrifilariae enter the eye, leading to visual impairment and eventually to blindness. These clinical manifestations are predominantly due to the body's inflammatory response to dead or dying microfilariae and vary depending on the number of worms.
Diagnosis is made by microscopic examination of skin snips for microfilariae. Adult worms may be found in subcutaneous nodules. There are several immunodiagnostic tests that have been developed for antigen detection with varying sensitivities and specificities. A small dose of diethylcarbamazine (DEC) when given to a patient (the "Mazzotti test") results in death of microfilariae and intense itching. This reaction is an indirect, sensitive method for diagnosing very light infections.
Treatment is with a single dose of ivermectin. As this drug kills only microfilariae, and not adult worms, treatment must be repeated every six to twelve months until the adult worms die of old age. Although DEC is also an effective treatment, it tends to induce more severe side effects than does ivermectin. Visible nodules can be removed to decrease the number of adult worms.
In 1974, the World Health Organization established the Onchocerciasis Control Program (OCP) to try to eliminate the Simulium fly by spraying the river systems in West Africa. With the discovery of ivermectin, a second strategy was added to the OCP. Populations in affected regions are given an annual dose of ivermectin to decrease the effects of the infection and to reduce further spreading by eliminating microfilariae. It is estimated that since the initiation of the program, 300,000 cases of blindness have been prevented. However, in large areas of Africa onchocerciasis continues to cause significant morbidity and mortality.
(SEE ALSO: Vector-Borne Diseases)
Bibliography
Burnham, G. (1998). "Onchocerciasis." The Lancet 351:1341–1346.
Hall, L. R., and Pearlman, E. (1999). "Pathogenesis of Onchocercal Keratitis (River Blindness)." Clinical Microbiology Reviews 12(3):445–453.
Molyneux, D. H., and Morel, C. (1998). "Onchocerciasis and Chagas' Disease Control: The Evolution of Control via Applied Research through Changing Development Scenarios." British Medical Bulletin 54(2):327–339.
Ottesen, E. A. (1993). "Filarial Infections." Infectious Disease Clinics of North America 7(3):619–633.
World Health Organization (2000). Onchocerciasis (River Blindness). Fact Sheet No. 95. Geneva: Author.
— MARTHA FULFORD; JAY KEYSTONE
| Veterinary Dictionary: onchocerciasis |
Infestation by the filarioid worm Onchocerca spp.; can cause a variety of diseases listed generally under the heading of onchocercosis.
| WordNet: onchocerciasis |
The noun has one meaning:
Meaning #1:
infestation with slender threadlike roundworms (filaria) deposited under the skin by the bite of black fleas; when the eyes are involved it can result in blindness; common in Africa and tropical America
Synonym: river blindness
| Wikipedia: Onchocerciasis |
| Onchocerciasis | |
| Classification and external resources | |
| ICD-10 | B73. |
|---|---|
| ICD-9 | 125.3 |
| DiseasesDB | 9218 |
| eMedicine | med/1667 oph/709 |
| MeSH | D009855 |
Onchocerciasis (pronounced /ˈɒnkɵsɜrˈsaɪ.əsɨs/ or /ˈɒnkɵsɜrˈkaɪ.əsɨs/),[1] also known as river blindness, is the world's third 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.[2] 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.[3]
The primary treatment is a 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 prevent transmission for many months in the remaining population.[4]
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Onchocerciasis may be divided into the following phases or types:[5]:440-441
Additionally, the various skin changes associated with onchocerciasis may be described as follows:[5]:440
About 18 million people are currently infected with this parasite; approximately 300,000 have been permanently blinded.[6] Onchoceriasis currently occurs endemically in 30 African countries, Yemen, and isolated regions of South America. Travelers who do not stay long in those countries have little risk of developing the disease as it requires prolonged exposure to the fly bites and parasite introduction.
Adult worms remain in subcutaneous nodules, limiting access to the host's immune system. Microfilariae, in contrast, are able to induce intense inflammatory responses, especially upon their death. Dying microfilariae have been recently discovered to release Wolbachia-derived antigens, triggering innate immune responses and producing the inflammation and its associated morbidity. Wolbachia species have been found to be endosymbionts of O. volvulus adults and microfilariae, and are thought to be the driving force behind most of O. volvulus morbidity. Severity of illness is directly proportional to the number of microfilariae and the power of the resultant inflammatory response.
Skin involvement typically consists of intense itching, swelling, and inflammation. A grading system has developed to categorize the degree of skin involvement:
Ocular involvement provides the common name associated with onchocerciasis, river blindness. The microfilariae migrate to the surface of the cornea. Punctate keratitis occurs in the infected area. This clears up as the inflammation subsides. However, if the infection is chronic, sclerosing keratitis can occur, making the affected area become opaque. Over time the entire cornea may become opaque, thus leading to blindness. There is some evidence to suggest that the effect on the cornea is caused by an immune response to bacteria present in the worms.
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The treatment for onchocerciasis is ivermectin (Mectizan); infected people can be treated once every twelve months. The drug paralyses the microfilariae and prevents them from causing itching. In addition, while the drug does not kill the adult worm, it does prevent them from producing additional offspring. The drug therefore prevents both morbidity and transmission. Additionally, Doxycycline can be added to the treatment regimen to kill the endosymbiotic bacteria, Wolbachia. This adjunct therapy has been shown to significantly lower microfilarial loads in the host and may have activity against the adult worms.[7][8]
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.
There are various control programs that aim to stop onchocerciasis from being a public health problem. The first was the Onchocerciasis Control Programme (OCP), which was launched in 1974 and at its peak covered 30 million people in eleven countries. Through the use of larvicide spraying of fast flowing rivers to control black fly populations and, from 1988 onwards, the use of ivermectin to treat infected people, the OCP eliminated onchocerciasis as a public health problem. The OCP, a joint effort of the World Health Organisation, the World Bank, the United Nations Development Programme and the UN Food and Agriculture Organization, was considered to be a success and came to an end in 2002. Continued monitoring ensures that onchocerciasis cannot reinvade the area of the OCP.
In 1992 the Onchocerciasis Elimination Programme for the Americas (OEPA) was launched. The OEPA also relies on ivermectin.
In 1995 the African Programme for Onchocerciasis Control (APOC) began covering another nineteen countries and mainly relying upon the use of ivermectin. Its goal is to set up a community-directed supply of ivermectin for those who are infected. In these ways, transmission has declined.
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.[9][10] A clinical trial of another parasitic agent, moxidectin (manufactured by Wyeth), began on July 1, 2009 (NCT00790998).[11]
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Did you mean: onchocerciasis, river blindness (disease), Onchocerciasis (in medicine)
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Encyclopedia of Public Health. Encyclopedia of Public Health. Copyright © 2002 by The Gale Group, Inc. All rights reserved. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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