蟠尾丝虫症

title: 生活史.
content: 蟠尾丝虫的生活史始于受到寄生之蚋属("Simulium")的雌性蚋(Black fly)吸血的过程,唾液含有第三期的幼虫(larva,非nymph),顺其口器进入下一个宿主体内,幼虫会从叮咬处移动到皮下组织或其他部位(如眼睛),并且形成椭圆形突起的结节(nodule),经6至12个月后化为成虫。身型较小的雄性成虫会从结节移行到皮下组织其他位置,随机遇上体型较大的雌虫进行交配,受精后的雌虫每天可产下1,000至3,000个卵,且可在人体内活上约15年,惊人的虫卵数量造成治疗时程漫长;而卵的成熟会在卵内形成第一期的微丝虫(microfilariae),再由母体一次一只排出至宿主皮下组织。正常的微丝虫在人体内则可活上1至2年,这些第一期的微丝虫又将在下一次受到蚋叮咬时被带走,而在这种昆虫体内,经过1至3周的发展形成第三期幼虫。值得注意的是,人类对蟠尾丝虫而言是唯一的最终宿主(definitive host),也就是说,人类如果消失,这种寄生虫就会随之灭绝。
title: 致病机转.
content: 成虫停留在皮下结节,因此宿主免疫系统受到限制;微丝虫则可以诱发强烈的发炎反应,尤其当它们死亡时更为剧烈,近年发现死亡中的微丝虫会释放抗原性的物质Wolbachia,这会启动先天性免疫反应,并产生发炎和相关病变。Wolbachia相关衍生物曾被证实是蟠尾丝虫成虫和微丝虫的内共生生物(endosymbionts),而病症的严重不只和发炎程度正相关,也和微丝虫的数量成正比。
title: 皮肤病变.
content: 典型的皮肤病变包含异常发痒、水肿、发炎。
title: 眼部病变.
content: 角膜表面是微丝虫移行的另一个部位,在此免疫系统仍可作用,当该部位受损、发生点状角膜炎,随着发炎消退,这些症状也会随之清除;但如果是慢性感染,角膜可能硬化,使得邻近区域模糊或无法透光,导致失明。
title: 治疗.
content: 治疗蟠尾丝虫主要用药为伊维菌素(Ivermectin,商品名:Mectizan),患者每12个月需接受一次治疗,利用药物瘫痪微丝虫,并避免它们所造成的痒,此外,由于该药物无法杀死成虫,却可以避免他们产下后代,因此这种药品可同时阻止病变和传播。
title: 疾病控制.
content: 1974年,第一个针对河川盲的蟠尾丝虫症控制计划(Onchocerciasis Control Programme, OCP)帮助11个国家,花费3千万美金,使用杀幼虫剂larvicide喷洒河川,控制蚋的数量。该计划动员世界卫生组织、世界银行、联合国开发计划署及联合国粮食及农业组织。  1988年,由于新制药物伊维菌素(Ivermectin)研发成功,OCP将蟠尾丝虫症正式由公共卫生问题移除。  1988年起,默克公司(Merck & Co.)藉药物捐助计划免费提供伊维菌素,偕同美国卫生部、世界卫生组织在河川盲地方病流行区发放。  1992年,美国开始推动蟠尾丝虫症根除计划,使用药物伊维菌素。  1995年,非洲蟠尾丝虫症控制计划的推动扩及19个国家,使用药物伊维菌素。  2002年,OCP计划告终,但并未完全解决河川盲的问题,因此未来仍需持续监控避免该传染病再度扩大。

Summary: 蟠尾丝虫症或蟠尾丝虫病(),又名河川盲、河盲症(river blindness),是一种因感染蟠尾丝虫引起的疾病。病状包括严重搔痒、皮下肿块,以及失明。是全球仅次于沙眼的可造成失明之第二大感染症。 蟠尾丝虫会透过的蚋(又名黑蝇,Black fly)叮咬而散播。通常需要经过多次叮咬才会感染。这些黑蝇生活在河流旁,这就是这种病得名河盲症的原因。蟠尾丝虫成虫一旦进入人体后,进行有性生殖产出微丝虫,接着移行至皮肤,眼睛等其他器官,接着在皮肤感染下一只叮咬病患的蚋。有几种方法能够用来诊断蟠尾丝虫病:将皮肤组织切片置于生理食盐水中观察有无幼虫出现;裂隙灯检查眼睛前房内有无发现幼虫;或是从(手术移除的)皮肤结节中发现成虫。 预防此疾病的疫苗尚未问世。预防措施就是避免遭受病媒咬伤。方法包含使用蚊香、穿着合适衣物。其他努力方向包含减少喷杀虫剂病媒的栖息。在世界上许多区域为了根除此病,而每年两次对整个族群投以治疗。对感染者的治疗方式通常是每六到十二个月投以一次伊维菌素,这种治疗方式可杀死体内幼虫却不能杀死成虫。使用多西环素可杀死微丝虫体内的内共生菌沃尔巴克氏体,并可减弱虫体活性,此治疗方式也受到部分医生推荐。另外也可以透过手术移除皮下肿块。 大约有170万人到250万人受到蟠尾丝虫症感染,约80万人因此视力受损。多数感染发生在撒哈拉以南非洲,少部分案例在也门、中美洲及南美洲的偏远地区被发现。1915年,医师首次发现了眼疾与蟠尾丝虫的关系。这个疾病被世界卫生组织列入被忽略的热带疾病清单。

Onchocerciasis: Onchocerciasis, also known as river blindness, 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 common name of the disease. Once inside a person, the worms create larvae that make their way out to the skin, where 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 are 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 larvae but not the adult worms. The antibiotic doxycycline weakens the worms by killing an associated bacterium called "Wolbachia", and is recommended by some as well. The lumps under the skin may also be removed by surgery. About 15.5 million people are infected with river blindness. Approximately 0.8 million have some amount of loss of vision from the infection. 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 (WHO) as a neglected tropical disease.