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| {{Onchocerciasis}} | | {{Onchocerciasis}} |
| {{CMG}} | | {{CMG}} {{AE}} {{KD}} |
| ==Overview==
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| '''Onchocerciasis''' (pronounced {{IPA|[ɒn.kəʊ.sɜːˈkaɪə.sɪs]}}) or '''river blindness''' is the world's second leading [[infectious]] cause of [[blindness]]. It is caused by ''Onchocerca volvulus'', a [[Parasitic worm]] that can live for up to fourteen years in the human body.
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| ==Life cycle==
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| [[Image:Life Cycle of Onchocerca volvulus PLoS Medicine.jpg|thumb|left|200px|The life cycle of ''O. volvulus'' (Illustration: Giovanni Maki)]]
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| The life cycle of ''O. volvulus'' begins when a parasitised female [[Black fly]] of the genus ''[[Simulium]]'' takes a [[blood]] meal. [[Saliva]] containing stage three ''O. volvulus'' [[larva]]e passes into the blood of the host. From here the larvae migrate to the [[subcutaneous]] tissue where they form nodules and then mature into adult worms over a period of six to twelve months.
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| After maturation, the smaller adult males migrate from nodules to subcutaneous tissue where they mate with the larger adult females, producing between 1000 and 3000 [[Egg (biology)|egg]]s per day.
| | {{SK}} Onchocercosis; river blindness; Robles disease |
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| The normal adult worm lifespan is up to 15 years. The eggs mature internally to form stage one microfilariae, which are released from the female's body one at a time and remain in the subcutaneous tissue.
| | ==[[Onchocerciasis overview|Overview]]== |
| | ==[[Onchocerciasis historical perspective|Historical Perspective]]== |
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| These stage one microfilariae are taken up by black flies upon a blood meal, in which they mature over the course of one to three weeks to stage three larvae, thereby completing the life cycle. Humans are the only definitive host for O. Volvulus. The normal microfilariae lifespan is 1-2 years.
| | ==[[Onchocerciasis pathophysiology|Pathophysiology]]== |
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| ==Causes of morbidity== | | ==[[Onchocerciasis causes|Causes]]== |
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| 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.
| | ==[[Onchocerciasis differential diagnosis|Differentiating Onchocerciasis from other Diseases]]== |
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| Skin involvement typically consists of intense itching, swelling, and inflammation. A grading system has developed to categorize the degree of skin involvement:
| | ==[[Onchocerciasis epidemiology and demographics|Epidemiology and Demographics]]== |
| *Acute papular [[dermatitis]] - scattered pruritic [[papules]];
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| *Chronic papular [[dermatitis]] - larger [[papules]], resulting in hyperpigmentation;
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| *Lichenified [[dermatitis]] - hyperpigmented [[papules]] and plaques, with [[edema]], [[lymphadenopathy]], pruritus and common secondary bacterial infections;
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| *Skin atrophy - loss of elasticity, skin resembles tissue paper, 'lizard skin' appearance;
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| *Depigmentation - 'leopard skin' appearance, usually on anterior lower leg.
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| Ocular involvement provides the common name associated with onchocerciasis, river blindness. The surface of the [[cornea]] is another area to which the microfilariae migrate, where they are also attacked by the immune system. In the area that is damaged, punctate [[keratitis]] occurs, which 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.
| | ==[[Onchocerciasis natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
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| ==Treatment and control== | |
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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.
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| 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 (epidemiology)|endemic]] areas.
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| 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
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| end in 2002. Continued monitoring ensures that onchocerciasis cannot reinvade the area of the OCP.
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| In 1992 the Onchocerciasis Elimination Programme for the Americas (OEPA) was launched. The OEPA also relies on ivermectin.
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| 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.
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| According to a study in the British medical journal The Lancet, the worm may be developing resistance to ivermectin. <ref>http://news.bbc.co.uk/2/hi/health/6753003.stm BBC News | Health: River blindness resistance fears. Accessed 15 Jun 2007.</ref>
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| ==See also==
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| *Carter Center River Blindness Program
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| CDC Parasites of Public Health Concern [http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm]
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| ==References==
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| {{Reflist}}
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| | ==Diagnosis== |
| | [[Onchocerciasis history and symptoms| History and Symptoms]] | [[Onchocerciasis physical examination | Physical Examination]] | [[Onchocerciasis laboratory findings|Laboratory Findings]] | [[Onchocerciasis other diagnostic studies|Other Diagnostic Studies]] |
| | ==Treatment== |
| | [[Onchocerciasis medical therapy|Medical Therapy]] | [[Onchocerciasis primary prevention|Primary Prevention]] | [[Onchocerciasis cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Onchocerciasis future or investigational therapies|Future or Investigational Therapies]] |
| | ==Case Studies== |
| | [[Onchocerciasis case study one|Case #1]] |
| ==External links== | | ==External links== |
| * [http://www.mectizan.org Mectizan Donation Program] | | * [http://www.mectizan.org Mectizan Donation Program] |
