ESSENTIALS OF DIAGNOSIS
Episodic attacks of lymphangitis, lymphadenitis, and fever.
Chronic progressive swelling of extremities and genitals; hydrocele; chyluria; lymphedema.
Microfilariae in blood, chyluria, or hydrocele fluid; positive serologic tests.
Lymphatic filariasis is caused by three filarial nematodes: Wuchereria bancrofti, Brugia malayi, and Brugia timori, and is among the most important parasitic diseases of man. Approximately 120 million people are infected with these organisms in tropical and subtropical countries, about a third of these suffer clinical consequences of the infections, and many are seriously disfigured. W bancrofti causes about 90% of episodes of lymphatic filariasis. It is transmitted by Culex, Aedes, and Anopheles mosquitoes and is widely distributed in the tropics and subtropics, including sub-Saharan Africa, Southeast Asia, the western Pacific, India, South America, and the Caribbean. B malayi is transmitted by Mansonia and Anopheles mosquitoes and is endemic in parts of China, India, Southeast Asia, and the Pacific. B timori is found only in islands of southeastern Indonesia. Mansonella are filarial worms transmitted by midges and other insects in Africa and South America.
Humans are infected by the bites of infected mosquitoes. Larvae then move to the lymphatics and lymph nodes, where they mature over months to thread-like adult worms, and then can persist for many years (eFigure 35–47). The adult worms produce large numbers of microfilariae, which are released into the circulation, and infective to mosquitoes, particularly at night (except for the South Pacific, where microfilaremia peaks during daylight hours).