elephantiasis , abnormal enlargement of any part of the body due to obstruction of the lymphatic channels in the area (see lymphatic system ), usually affecting the arms, legs, or external genitals. In tropical countries the most common cause is filariasis, infestation with certain filaria, small parasitic roundworms (see worm ) of the genera Wuchereria bancrofti or Brugia malayi that are introduced into the body by many species of mosquitoes. The adult worms live in the lymphatic system, causing local inflammation, fibrosis, and obstruction, and resulting in the characteristic enlargement and thickening of the skin. The initial damage done by the worms can be greatly worsened by secondary bacterial and fungal infections.

Recovery from filariasis is possible and surgery sometimes helps, but any elephantiasis that develops during the disease cannot be cured. Ivermectin, an antifilarial drug, has been effective with a single dose. Diethylcarbamazine often kills the adult worms or impairs their reproductive capabilities, and the antibiotic doxycycline, which works by killing symbiotic bacteria that live inside the worms, also eliminates adult worms. Albendazole, in combination with others drugs, is being used in a program of mass drug administration undertaken under the auspices of the World Health Organization in an attempt to eliminate filariasis. Begun in 1999 the program treats an entire population in an attempt to eradicate the worm. Control of mosquitoes also is instrumental in holding down the incidence of the disease. Careful hygiene and other measures that prevent and control subsequent bacterial and fungal infections in limbs or genitals in which the lymphatic system has been damaged can reduce disfigurement and suffering. Blocking of the lymph channels and elephantiasis can also result from lymphogranuloma venereum, a sexually transmitted disease .