Onchocerciasis
From Wikipedia, the free encyclopedia
| 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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[edit] Classification
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
[edit] Epidemiology
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.
[edit] Causes of morbidity
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:
- Acute papular dermatitis - scattered pruritic papules;
- Chronic papular dermatitis - larger papule, resulting in hyperpigmentation;
- Lichenified dermatitis - hyperpigmented papules and plaques, with edema, lymphadenopathy, pruritus and common secondary bacterial infections;
- Skin atrophy - loss of elasticity, skin resembles tissue paper, 'lizard skin' appearance;
- Depigmentation - 'leopard skin' appearance, usually on anterior lower leg.
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.
[edit] 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. 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]
[edit] See also
- Carter Center River Blindness Program
- Neglected Diseases
- Rodolfo Robles
- List of parasites (human)
[edit] References
- ^ OED
- ^ "Global Partnership to Eliminate Riverblindness". The World Bank. http://www.worldbank.org/afr/gper/disease.htm. Retrieved on 2007-11-04.
- ^ "Causes of river blindness". Sightsavers International. http://www.sightsavers.org/What%20We%20Do/Eye%20Conditions/River%20Blindness/World1629.html. Retrieved on 2008-01-28.
- ^ "eMedicine - Onchocerciasis (River Blindness) : Article by Jason F Okulicz, MD". http://www.emedicine.com/derm/topic637.htm#section~treatment. Retrieved on 2008-01-28.
- ^ a b James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0.
- ^ "What is river blindness?". Sightsavers International. http://www.sightsavers.org/What%20We%20Do/Eye%20Conditions/River%20Blindness/World1622.html. Retrieved on 2008-01-28.
- ^ Trattler, Bill; Gladwin, Mark (2007). Clinical Microbiology Made Ridiculously Simple. MedMaster Inc. ISBN 0-940780-81-X.
- ^ Taylor MJ, Bandi C, Hoerauf A (2005). "Wolbachia bacterial endosymbionts of filarial nematodes". Adv. Parasitol. 60: 245–84. doi:. PMID 16230105. http://linkinghub.elsevier.com/retrieve/pii/S0065-308X(05)60004-8.
- ^ "River blindness resistance fears". BBC News. http://news.bbc.co.uk/2/hi/health/6753003.stm. Retrieved on 2007-06-15.
- ^ Osei-Atweneboana MY, Eng JK, Boakye DA, Gyapong JO, Prichard RK (June 2007). "Prevalence and intensity of Onchocerca volvulus infection and efficacy of ivermectin in endemic communities in Ghana: a two-phase epidemiological study". Lancet 369 (9578): 2021–9. doi:. PMID 17574093. http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(07)60942-8.
- ^ "Fighting river blindness and other ills". Lancet 374 (9684): 91. 11 July 2009. doi:.
[edit] External links
- Onchocerciasis Research Project at the University of Tuebingen
- Mectizan Donation Program
- River Blindness Documentary "37 Million and Counting" by Aaron Edell
- SightSavers
- What is River Blindness?, CBM International
- CDC Parasites of Public Health Concern
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