Merck Manual

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Overview of Filarial Nematode Infections


Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
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Threadlike adult filarial worms reside in lymphatic or subcutaneous tissues. Gravid females produce live offspring (microfilariae) that circulate in blood or migrate through tissues. When ingested by a suitable bloodsucking insect (mosquitoes or flies), microfilariae develop into infective larvae that are inoculated or deposited in the skin of the next host during the insect bite. Life cycles of all filarial worms are similar except for the site of infection. Only a few filarial species infect humans. The major filarial diseases below can be grouped based on the location of adult worms. (See also Approach to Parasitic Infections Approach to Parasitic Infections Human parasites are organisms that live on or in a person and derive nutrients from that person (its host). There are 3 types of parasites: Single-cell organisms (protozoa, microsporidia) Multicellular... read more .)

Subcutaneous filariasis includes

Lymphatic filariasis includes

Other types of filariasis include

Some specialty laboratories have screening serologic tests for filarial infection (including Wuchereria, Brugia, Onchocerca, and Mansonella infections). The tests are sensitive but cannot identify the specific filarial infection or distinguish active from remote infection. This distinction is less important in symptomatic travelers, but limits the usefulness of the tests in people from endemic areas.

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