It is commonly, known as ‘filaria worm’ found in the lymphatic vessels, muscular tissues and glands of man. The worm is distributed in all tropical, sub-tropical and temperate countries and causes filariasis.
The female is about 8 cm in length. The body is creamy-white, cylindrical and filiform with blunt ending on the anterior and posterior sides. The posterior end of the male is curved. The mouth is of very simple type without any lip. The intermediate host is a mosquito. The adult worms, living in the lymph vessels, copulate when the individuals of both the sexes are present.
Life history:
The female after fertilization does not lay eggs directly but eggs are retained in the female. The female gives birth to a number of larvae, which are surrounded by a delicate membranous sheath. These microfilariae live in the lymph vessels or migrate into the blood capillaries underneath the skin.
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Microfilariae appear in the skin capillaries during night between 10 pm to 2 am and during daytime they live in large deep seated blood vessels. If the secondary host bites the man, containing microfilariae in between 10 pm to 2 am the larvae enter into the mosquito’s stomach from where they migrate to the thoracic muscles where they grow and attain length of about 1.5 mm in a few weeks.
Now the larvae migrate to the proboscis of intermediate host. In this stage if the mosquito bites a man the larvae are transferred to the blood stream of man from where they go to the lymph glands and lymph passages and grow into mature stage.