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Filariasis (or philariasis) is a parasitic disease caused by an infection with roundworms of the Filarioidea type.〔(【引用サイトリンク】title=Lymphatic Filariasis )〕 These are spread by blood-feeding black flies and mosquitoes. This disease belongs to the group of diseases called helminthiasis. Eight known filarial nematodes use humans as their definitive hosts. These are divided into three groups according to the niche within the body they occupy: *Lymphatic filariasis is caused by the worms ''Wuchereria bancrofti'', ''Brugia malayi'', and ''Brugia timori''. These worms occupy the lymphatic system, including the lymph nodes; in chronic cases, these worms lead to the disease elephantiasis. *Subcutaneous filariasis is caused by ''Loa loa'' (the eye worm), ''Mansonella streptocerca'', and ''Onchocerca volvulus''. These worms occupy the subcutaneous layer of the skin, in the fat layer. ''L. loa'' causes ''Loa loa'' filariasis, while ''O. volvulus'' causes river blindness. *Serous cavity filariasis is caused by the worms ''Mansonella perstans'' and ''Mansonella ozzardi'', which occupy the serous cavity of the abdomen. The adult worms, which usually stay in one tissue, release early larval forms known as microfilariae into the host's bloodstream. These circulating microfilariae can be taken up with a blood meal by the arthropod vector; in the vector, they develop into infective larvae that can be transmitted to a new host. Individuals infected by filarial worms may be described as either "microfilaraemic" or "amicrofilaraemic", depending on whether microfilariae can be found in their peripheral blood. Filariasis is diagnosed in microfilaraemic cases primarily through direct observation of microfilariae in the peripheral blood. Occult filariasis is diagnosed in amicrofilaraemic cases based on clinical observations and, in some cases, by finding a circulating antigen in the blood. ==Signs and symptoms== The most spectacular symptom of lymphatic filariasis is elephantiasis—edema with thickening of the skin and underlying tissues—which was the first disease discovered to be transmitted by mosquito bites. Elephantiasis results when the parasites lodge in the lymphatic system. Elephantiasis affects mainly the lower extremities, while the ears, mucous membranes, and amputation stumps are affected less frequently. However, different species of filarial worms tend to affect different parts of the body; ''Wuchereria bancrofti'' can affect the legs, arms, vulva, breasts, and scrotum (causing hydrocele formation), while ''Brugia timori'' rarely affects the genitals. Those who develop the chronic stages of elephantiasis are usually amicrofilaraemic, and often have adverse immunological reactions to the microfilariae, as well as the adult worms.〔 The subcutaneous worms present with rashes, urticarial papules, and arthritis, as well as hyper- and hypopigmentation macules. ''Onchocerca volvulus'' manifests itself in the eyes, causing "river blindness" (onchocerciasis), one of the leading causes of blindness in the world. Serous cavity filariasis presents with symptoms similar to subcutaneous filariasis, in addition to abdominal pain, because these worms are also deep-tissue dwellers. 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「Filariasis」の詳細全文を読む スポンサード リンク
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