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Filarial worms are parasitic nematodes that dwell within the lymphatics and the subcutaneous tissues. Eight filarial species are associated with human disease, though only 4 cause significant morbidity in children (Table 328-1). These species include the causative agents of lymphatic filariasis—Wuchereria bancrofti, Brugia malayi, and Brugia timori—and the subcutaneous filariid Onchocerca volvulus, the causative agent of onchocerciasis. The other filarial parasites of humans (Loa loa, Mansonella perstans, Mansonella streptocerca, and Mansonella ozzardi) cause minimal childhood morbidity. Of the 8 filarial parasites of humans, W bancrofti is, by far, the most important in terms of both morbidity and numbers of people infected.

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Table 328-1. Epidemiologic and Biological Features of the Filariae
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Each filarial parasite is transmitted by biting arthropods, either mosquitoes or flies, and all go through complex life cycles that include a slow maturation (often 3–24 months) from the infective larval stages carried by the insects to adult worms that live within the lymphatics and lymph nodes (W bancrofti and Brugia spp) or in the subcutaneous tissues (Onchocerciasis volvulus, L loa, M streptocerca). Patent infection occurs when male and female adult worms produce microfilariae offspring, 200 to 400 mm in length, that either circulate in the blood or migrate to the skin while awaiting ingestion by insect vectors. Productive infection is usually not established unless exposure to infective larvae is intense or prolonged. Therefore, while acquisition of and infection with these parasites occurs throughout childhood in endemic regions, most of the pathology associated with these infections is found primarily in older children and adults.

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Lymphatic filariasis affects approximately 120 million people in Africa, Asia, India, Indonesia, the Philippines, Papua New Guinea, and focal areas of Latin America and ...

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