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Onchocerciasis, also known as river blindness and Robles disease, is a disease caused by infection with the parasitic worm ''Onchocerca volvulus''. Symptoms include severe itching, bumps under the skin, and blindness.〔 It is the second most common cause of blindness due to infection, after trachoma.〔 The parasite worm is spread by the bites of a black fly of the ''Simulium'' type.〔 Usually many bites are required before infection occurs. These flies live near rivers, hence the name of the disease. Once inside a person, the worms create larvae that make their way out to the skin.〔 Here they can infect the next black fly that bites the person.〔 There are a number of ways to make the diagnosis including: placing a biopsy of the skin in normal saline and watching for the larva to come out, looking in the eye for larvae, and looking within the bumps under the skin for adult worms. A vaccine against the disease does not exist.〔 Prevention is by avoiding being bitten by flies. This may include the use of insect repellent and proper clothing.〔 Other efforts include those to decrease the fly population by spraying insecticides.〔 Efforts to eradicate the disease by treating entire groups of people twice a year is ongoing in a number of areas of the world.〔 Treatment of those infected is with the medication ivermectin every six to twelve months.〔〔 This treatment kills the larva but not the adult worms. The medication doxycycline, which kills an associated bacterium called ''Wolbachia'', appears to weaken the worms and is recommended by some as well.〔 Removal of the lumps under the skin by surgery may also be done. About 17 to 25 million people are infected with river blindness, with approximately 0.8 million having some amount of loss of vision.〔〔 Most infections occur in sub-Saharan Africa, although cases have also been reported in Yemen and isolated areas of Central and South America.〔 In 1915, the physician Rodolfo Robles first linked the worm to eye disease. It is listed by the World Health Organization as a neglected tropical disease. ==Signs and symptoms== 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. ''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. Dying microfilariae have been recently discovered to release ''Wolbachia'' surface protein that activates TLR2 and TLR4, triggering innate immune responses and producing the inflammation and its associated morbidity. The severity of illness is directly proportional to the number of infected microfilariae and the power of the resultant inflammatory response. Skin involvement typically consists of intense itching, swelling, and inflammation. A grading system has been developed to categorize the degree of skin involvement: *Acute papular onchodermatitis – scattered pruritic papules *Chronic papular onchodermatitis – larger papules, resulting in hyperpigmentation *Lichenified onchodermatitis – hyperpigmented papules and plaques, with edema Lymphadenopathy, pruritus and common secondary bacterial infections *Skin atrophy – loss of elasticity, the skin resembles tissue paper, 'lizard skin' appearance *Depigmentation – 'leopard skin' appearance, usually on anterior lower leg *Glaucoma effect – eyes malfunction, begin to see shadows or nothing Ocular involvement provides the common name associated with onchocerciasis, river blindness, and may involve any part of the eye from conjunctiva and cornea to uvea and posterior segment, including the retina and optic nerve.〔 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. Some evidence suggests the effect on the cornea is caused by an immune response to bacteria present in the worms. The skin is itchy, with severe rashes permanently damaging patches of skin. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Onchocerciasis」の詳細全文を読む スポンサード リンク
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