Merck Manual

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Overview of Filarial Nematode Infections


Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Last review/revision Sep 2022
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Filarioidea are a superfamily of threadlike, parasitic worms, with numerous families, genus, and species. Their definitive hosts are vertebrates, but only a few filarial species infect humans. 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.

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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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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