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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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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 ...