Lymphadenitis caused by infection with filarial parasites.

Filaria organisms are nematode worms of various species with a distinct geographic distribution. Wuchereria bancrofti is prevalent in Africa and Central and South America. Brugia malayi and B. timor are more common in Asia and South America (1,2). In North America, cases of Brugia filariasis acquired from animals, B. beaveri from raccoons and B. lepori from rabbits, have been reported (3,4). Most cases have been from the northeastern United States; occasional cases have occurred in the South, Midwest, and even New York City (5). According to the World Health Organization, lymphatic filariasis affects more than 90 million people throughout the world (6).

Bancroftian filariae may be as long as 100 mm and up to 200 μm wide, whereas Brugia filariae are slender and threadlike, with a diameter of 40 to 75 μm.

The female worms discharge microfilariae into the blood, which is ingested by various species of mosquitoes. In the mosquitoes, which act as intermediate hosts and vectors, the microfilariae metamorphose into infective larvae, which through the insect bite penetrate the skin, enter the circulation, and migrate to a suitable location, where they develop into adult worms (1).

In humans, adult Filaria worms colonize lymphatic vessels and lymph nodes, where they can live for years. The intense inflammatory reaction to the presence of Filaria depends largely on the hypersensitivity or tolerance to the antigens of degenerating parasites (7). It is believed that tolerance to the presence of filariae may be the result of exposure to its antigens in the maternal circulation in utero (8). Secondary bacterial inflammation is also an important contributing factor in changing lymphedema to elephantiasis (7).

In men, filariae are most commonly found in the lymphatics of the epididymis and testis, and in women in the lymphatics of the breast (6). They also invade the lymphatics of the legs and the inguinal and pelvic lymph nodes. The lymphatics become occluded and inflamed. Dead and degenerated parasites in particular elicit intense inflammatory reactions, which have been misinterpreted in some cases as testicular torsion and mammary fibroadenoma or carcinoma (6).

Infection by Onchocerciasis or other microfilariae may cause dermatitis, subcutaneous nodules, sclerosing lymphadenitis, and eye disease (8).