Describe the life cycle of wucheria bancrofti.

Explanation

Wucheria bancrofti is commonly called the filarial worm as it causes filariasis in human beings. It is digenitic parasite that lives in the lymph vessels of man. Sir Patrick manson identified female culex mosquito as its secondary host.
Life cycle : It completes its life cycle in two hosts namely man and female culex mosquito. In man: Both male and female worms are found coiled together in the lymphatic vessels of man. After copulation the female releases the sheathed microfilaria larvae into the lymph of man. Each sheathed microfilaria larva measures 0.2 to 0.3 mm in length. It is surrounded by a loose cuticular sheath which is supposed to be the modified shell. They migrate to the blood circulation and reside in the deeper blood vessels during the day time. They move to the peripheral blood circulation during the night time between 10.00 pm and 4.00 am. This tendency is referred to as nocturnal periodicity. When a female culex mosquito sucks the blood of an infected person. They enter the gut of mosquito. They die if they are not transferred to mosquito with in 70 days.
In mosquito : In the mid gut of mosquito, the sheath of the larva is dissolved within 2 to 6 hours of the infection.
The ex-sheathed microfilaria larva penetrates the gut wall and reaches the heamocoel of mosquito. From there, it reaches the thoracic muscles and transforms into a sausage shaped larva within two days. It is called the first stage larva or first stage microfilaria, This undergoes two moultings within 10 to 20 days and transforms into along infective 3 stage microfilaria. It reaches the labium of the mosquito.
In man after the infection : When an infected mosquito bites a man, the `3^(rd)` stage microfiliria larvae enter the blood circulation of man and finally reach the lymphatic vessels : Here they undergo the `3^(rd)` and the `4^(th)` moultings to produce yound filarial worms. They attain sexual maturity with in 5 to 18 months.