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INTRODUCTION

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 323-1). These species include the causative agents of lymphatic filariasis—Wuchereria bancrofti, Brugia malayi, and Brugia timori—and Onchocerca volvulus, the causative agent of onchocerciasis. The filarial parasites can be distinguished by their geographic distribution, vector, anatomic location of adult worms, and anatomic location and periodicity of microfilaria detection. Of the human filarial parasites, W bancrofti is, by far, the most important in terms of both morbidity and numbers of people infected. O volvulus remains an important cause of worldwide morbidity, especially in Africa. With elimination of O volvulus from selected transmission zones in the Americas, there is hope of eventual elimination from Africa.

TABLE 323-1EPIDEMIOLOGIC AND BIOLOGIC FEATURES OF THE FILARIAE

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 the adult worms that live within the lymphatics and lymph nodes (W bancrofti and Brugia species) or in the subcutaneous tissues (O volvulus, Loa loa, Mansonella streptocerca). Infection occurs when male and female adult worms mate and females 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. Maturation of ...

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