Filariasis is an infection caused by a parasitic worm and is transmitted by insect-bites. It is more prevalent in the tropical areas of Africa, Asia, Central and South America. In India, it is common in eastern Uttar Pradesh and Bihar. This disease spreads from person to person by mosquito bites. When a mosquito bites an infected person, microscopic worms circulating in his blood enter and infect the mosquito. These worms then pass to the other person when this infected mosquito bites him. The worms transferred from the mosquito, move through the skin, and travel to lymph vessels, where they grow into adults. An adult worm lives for about seven years. The adult worms mate and release millions of microscopic worms into the blood. There are eight different types of this worm, out of which three are responsible for causing the disease: Wucheria bancrofti and Brugia malayi cause lymphatic filariasis, and Onchocera volvulus causes onchocerciasis (river blindness).