Wuchereria (Wbancrofti and Wmalayi), the filarial worms cause a slowly developing chronic inflammation of the organs in which they live for many years, usually the lymphatic vessels of the lower limbs, and the disease is calledfilariasis. Thepathogen spreads from one human being to another through mosquitoes like Culex and to a less extent by Anopheles and Aedes. The parasite resides in lymph vessels, connective tissues and mesentery. It is manifestated by lymphoedema accompanied by thickening of subcutaneous tissues and skin so that there is permanent swelling mostly of feet, legs, thighs, scrotal sacs, breast etc. In Culex and other mosquitoes females are blood sucking while males suck juices of flowers and fruits. Female Culex carries filarial worm from one person to another. It prefers to breed in dirty water near human habitation.