Filaria is a parasitic worm from the Nematoda class. Its length can vary from 2 mm to 1.3 m. It lives in the tropics and subtropics. The adult individuals parasite in different parts of the human body (where they get through contaminated water or food) but usually prefer the limbs. They live under the skin where they make protuberances. This leads to swellings and inflammations, later boils. If the worm tears while pulling out of the skin, occur severe inflammation and a poisoning, sometimes with a lethal end. These symptoms are obviously due to the body fluids of the worm because if it is pulled out the whole, the recovery is very fast. 
In Guatemala and Mexico there is a similar parasite which can reach a length up to 50 cm. Its poison causes visual impairments, even loss of sight, convulsions, muscle pain, sleeplessness. After removing the worm, the recovery is almost immediate.