Elephantiasis

The majority of the suffering caused by filarial nematodes occurs because of blockage of the lymphatic system. The lymphatic system is made up of a network of vessels which serve to drain tissue fluid from all the major organs of the body, including the skin, and from all four limbs. These vessels pass through lymph nodes on their way to empty into major veins at the base of the neck and within the abdomen. While it was originally thought that blockage of lymph flow occurred due to the live adult worms coiling within the lymphatic vessels, it is now thought that the worst obstructions occur after the adult worms die.

While the worm is alive, the human immune system attempts to rid itself of the foreign invader by sending a variety of cells to the area, causing the symptoms of inflammation (redness, heat, swelling) in the infected node and lymph channels. The skin over these areas may become thickened and rough. In some cases, the host will experience systemic symptoms as well, including fever, headache, and fatigue. This complex of symptoms lasts seven to ten days, and may reappear as often as ten times in a year.

After the worm's death, the inflammatory process is accelerated, and includes the formation of tough, fibrous tissue which ultimately blocks the lymphatic vessel. Lymph fluid cannot pass through the blocked vessel, and the back up of fluid results in swelling (also called edema) below the area of blockage. Common areas to experience edema are arms, legs, and the genital area (especially the scrotum). These areas of edema are also prone to infection with bacterial agents. When extreme, lymphatic obstruction to vessels within the abdomen and chest can lead to rupture of those vessels, with spillage of lymph fluid into the abdominal and chest cavities.

An individual who picks up filarial disease while traveling does not tend to experience the more extreme symptoms of elephantiasis that occur in people who live for longer periods of time in areas where the disease is common. It is thought that people who live in these areas receive multiple bites by infected mosquitoes over a longer period of time, and are therefore host to many, many more nematodes than a traveler who is just passing through. The larger worm load, as the quantity of nematodes present within a single individual is called, contributes to the severity of the disease symptoms suffered by that individual.