The filarial worms are the parasitic worms which causes filariasis.This disease is caused by the worm Wuchereria bancrofti or filarial bancrofti.The adult worm dwells in the lymphatic vessels and lymph glands .The body of the parasite is  thread like tapering anteriorly with swollen front end.The pharynx of the parasite is muscular anteriorily and glandular posteriorily and these worms have no lips.The female is 10 cm long and.25 mm thick in diameter.The tail of the mail is coiled like a tendril with many papillae and with one long and short spicule.The female give birth to the microfilariae  which are enclosed within a delicate sheath.These microfilariae is passed in to the  blood vessels from  thelymphatic system.The development of the microfilrae occurs as the blood is sucked by the mosquito which serves as an intermediate host.When this infected mosquito bites the man the larvae creeps out of the labium on to the human skin and after their moulting they resides as adults in the human lymphatic system.The incubation period ranges from the time interval from the attack of the infective larvae to the clinical manifestation.this incubation period is 16 months and can be longer also.The accumulation of this wuchereria  may block the lymphatic system and this may cause the inflammation of the lymph glands.the blockage of the lymph vessels may also lead to elephantiasis .The prevention method includes chemotherapy.The protection from mosquito bites may also  prevent filarial infection.The effective drug for the treatment of filariasis is diethylcaramzine used for chemotherapy