Describe the life cycle of Wuchereria bancrofti.

Wuchereria bancrofti is commonly called the filarial worm. It is a digenetic parasite that lives in the lymph vessels of man. It causes filariasis or elephantiasis in man.
Life cycle : Wuchereria bancrofti completes its life cycle in two hosts namely man and female Culex mosquito.
i) Life cycle in man : After copulation, female releases the sheathed microfilaria larvae into the lymph of man.
Microfilaria larvae migrate to the blood circulation and live in the deeper blood vessels during the day time.
They move to the peripheral circulation during the night time between 10.00 pm and 4.00 am. This migration is called nocturnal periodicity.
When a female Culex mosquito sucks the blood of an infected person, they enter the gut of mosquito.
ii) Life cycle in mosquito : In the mid gut of mosquito, the sheath of the larvae is dissolved. The microfilaria larvae penetrates the gut wall and reaches haemocoel.
From there it reaches thoracic muscles and transforms into a ‘sausage shaped larva’ or first stage larva.
It undergoes two moultings and transforms into a long infective 3^rd stage microfilaria.
This stage reaches the labium of the mosquito.
It is infective to man. It enters human blood during mosquito bit. It moves into lymph vessels and completes 3^rd and 4^th moult and becomes young one. Later it becomes Adult.