Elephantiasis is not a disease, but a condition. It is caused when the lymphatic system, which drains tissue fluid from the skin and muscles back into the bloodstream becomes blocked. The tissue becomes swollen with excess fluid, and after time, becomes enlarged and thickened - the skin develops the texture and appearance of that of an elephant. We see it in patients who have had disruption of their lymphatic system due to surgery or radiation, often involving cancer, which tends to invade the lymphatic system as it spreads.
In some tropical areas there exists tiny parasitic filarial worms, spread by the bites of various mosquitoes and flies, that inhabit the lymphatic system, eventually clogging it and causing elephantiasis. This disorder - also called "filariasis" when caused by these parasites - takes years to develop, probably requires multiple bites by infected flies, and rarely effects the casual tourist. An estimated 200 million people have this infected to varying degrees. The severe disfiguring disease is now quite rare, thanks to treatment and prevention programs. Like the programs to prevent river blindness, periodic treatment of entire populations (such as through the Merck Mectizan Donation Program) with a single dose of ivermectin can keep the disease and the spread of the disease controlled,
Different strains of filariasis, transmitted by different insects, exist in different parts of the world. If interested, you can see a chart of these different strains.