- Key People:
- Sir Patrick Manson
filariasis
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What is filariasis?
Filariasis refers to a group of infectious diseases caused by thread-like filarial worms that invade subcutaneous tissues and the lymphatic system of mammals. These parasitic worms require two hosts, an arthropod and a vertebrate, to complete their life cycle.
Different forms of filariasis include Bancroftian filariasis, filariasis malayi, onchocerciasis (river blindness), and loiasis. The disorders can cause acute inflammation and chronic scarring. In some untreated cases, it can result in elephantiasis, which causes gross expansion of the tissues of the legs and scrotum. Diethylcarbamazine is a therapeutic drug effective in treating filariasis. Prevention relies heavily on insecticides and insect repellents.
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How does a person get filariasis?
Filariasis is a group of infectious diseases caused by thread-like nematodes that invade the subcutaneous tissues and lymphatics of mammals.
Bancroftian filariasis, caused by Wuchereria bancrofti, is transmitted to humans by mosquitoes, typically Culex quinquefasciatus. The nematode lives in the lymph nodes and lymph vessels, notably those draining the legs and genital area. Over years, the lymph channels may harden and become clogged with fibrous tissue, which can result in elephantiasis.
Other forms of filariasis include filariasis malayi, onchocerciasis, and loiasis. Filariasis is preventable with insecticides and insect repellents.
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Which organisms cause filariasis?
Filariasis is caused by parasitic worms of the family Filariidae, also known as filarial worms. These worms require two hosts, an arthropod (intermediate) and a vertebrate (primary), to complete their life cycle.
Different filarial worms cause specific types of filariasis:
* Wuchereria bancrofti causes Bancroftian filariasis, common in tropical and subtropical regions.
* Brugia malayi causes filariasis malayi, similar to Bancroftian filariasis, and is found mainly in eastern Asia.
* Onchocerca volvulus causes Onchocerciasis (river blindness), transmitted by flies of the genus Simulium.
* Loa loa causes Loiasis, which is prevalent in western and central Africa, and is transmitted by flies of the genus Chrysops.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What symptoms does filariasis cause in the body?
Filariasis, caused by threadlike nematodes, leads to a range of symptoms, starting with acute inflammation and potentially advancing to chronic scarring. The infection cycle involves the transmission of microfilariae to humans through intermediate hosts like mosquitoes and flies.
Initial symptoms include granulomatous lesions, swelling, and impaired circulation, followed by the enlargement of lymph nodes and dilation of lymph channels. In untreated cases, the hardening and clogging of lymph channels with fibrous tissue can result in elephantiasis, characterized by the gross expansion of tissues, particularly in the legs and scrotum. Different forms of filariasis, such as onchocerciasis and loiasis, have distinct symptoms, including skin nodules, eye invasion, and transient areas of allergic inflammation.
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How is filariasis diagnosed and treated?
Filariasis diagnosis typically involves identifying microfilariae in blood samples. The disease is caused by parasitic filarial worms that infect the lymph channels.
Treatment options include:
* Diethylcarbamazine: An oral synthetic anthelmintic drug effective against filarial worms, used to treat filariasis caused by Wuchereria bancrofti, Onchocerca volvulus, and Loa loa.
* Ivermectin: An antiparasitic drug that eliminates microfilariae, used to treat onchocerciasis.
* Surgical Excision: Nodules can be surgically removed.Insecticides and repellents also play a vital role in filariasis prevention.
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What are the long-term effects and possible complications of filariasis?
Filariasis encompasses various infectious diseases caused by thread-like nematodes that invade subcutaneous tissues and lymphatics. Long-term effects of untreated filariasis, particularly Bancroftian filariasis, can result in the hardening and clogging of lymph channels with fibrous tissue, leading to elephantiasis, characterized by the gross expansion of tissues, especially in the legs and scrotum.
Other forms of filariasis, such as Onchocerciasis (river blindness), can cause skin nodules and may lead to blindness in infected individuals. Loiasis is characterized by transient areas of allergic inflammation and irritation, though permanent damage is rare. Effective treatments include drugs like diethylcarbamazine, thiacetarsamide sodium, surgical removal of worms, and chemotherapeutics. Prevention relies heavily on insecticides and insect repellents.
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filariasis, a group of infectious disorders caused by threadlike nematodes of the superfamily Filarioidea that invade the subcutaneous tissues and lymphatics of mammals, producing reactions varying from acute inflammation to chronic scarring. In the form of heartworm disease, it may be fatal to dogs and other mammals.
Cycle of infection and symptoms
The cycle of infection in humans is complex because of the different intermediate hosts, such as mosquitoes and flies, that transmit infectious parasites to humans. In general, female nematodes give birth to elongated embryos, the microfilariae, which are taken up by an intermediate host. Microfilariae migrate through the peripheral blood and skin, from which they are taken by bloodsucking insects. Within the insect carrier, the microfilariae grow into motile infective larvae that, at the insect’s next blood meal, are introduced into the human host, where they reach maturity in about a year. The initial inflammatory stage is characterized by granulomatous lesions, swelling, and impaired circulation; this stage is followed by enlargement of the lymph nodes and dilation of the lymph channels.
Types of filariasis
The term filariasis is commonly used to designate Bancroftian filariasis, caused by Wuchereria bancrofti, organisms that are widely distributed in tropical and subtropical regions of the world and are transmitted to humans by mosquitoes, usually Culex quinquefasciatus (see also Culex mosquito). The nematode lives principally in the lymph nodes and lymph vessels, notably those draining the legs and genital area, where the adult worms induce allergic reactions in the sensitized tissues. Over years, the lymph channels may harden and become infiltrated and clogged with fibrous tissue elements, resulting in some untreated cases in the condition known as elephantiasis, which is typically associated with the gross expansion of the tissues of the legs and scrotum. The most effective therapeutic drugs are diethylcarbamazine and thiacetarsamide sodium, which kill the adult worms and microfilariae.
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The form of filariasis known as filariasis malayi closely resembles Bancroftian filariasis in its symptoms and pathological changes; it is caused by Brugia malayi, found chiefly in eastern Asia. Onchocerciasis (river blindness) is caused by Onchocerca volvulus, which is transmitted to humans by flies of the genus Simulium. These flies breed along fast-moving streams. The condition is widespread in southern Mexico and Guatemala and is common in central Africa. Characteristic lesions are nodules beneath the skin, usually in the head region; the infection may also invade the eyes, causing blindness in about 5 percent of infected individuals. Treatment consists of the surgical excision of the nodules and the administration of chemotherapeutics.
Loiasis, prevalent in western and central Africa, especially along the Congo River, is caused by Loa loa and transmitted by flies of the genus Chrysops. It is characterized by transient areas of allergic inflammation in the tissues beneath the skin, called calabar swellings; adult worms may sometimes be visible beneath the conjunctiva (the delicate membrane lining the eyelids and covering the exposed surface of the eyeball). Loiasis produces irritation but seldom permanent damage. Treatment includes surgical removal of the worms from the conjunctiva and drug therapy. Other forms of filariasis are caused by Acanthocheilonema perstans and Mansonella ozzardi and are not in most cases associated with specific symptoms. The prevention of filariasis relies heavily on insecticides and insect repellents.