The microfilariae from different species of filarial worms can be identified in thick blood smears, after Giemsa staining, by the presence or absence of the sheath, and the arrangement of the nuclei in the tail. The L3 infective larvae are introduced into the wound left by the bite of the insect vector, which can, depending on the location and periodic cycle, be species of the mosquitoes of the genera Culex, Anopheles Aedes or Mansonia. The larvae makes their way through the peripheral lymphatics moving to the larger vessels and into the lymph glands where they mature into adult worms. The adults come to live close to the lymphatic glands predominantly in the lower half of the body. The worms can produce microfilaria for more than 15 years.
Transmission occurs when the mosquito takes a blood meal.
The microfilaria loses the sheath after about 2 hours in the mosquito gut. The larva penetrates the gut wall and migrates to the thoracic muscles, where after about 8 days it molts to the L2 stage which is a short sausage shaped worm. The L3 migrates through the haemocoel of the insect to the mouthparts of the mosquito where they reside in the labium which forms the sheath for the proboscis. The infective larvae escape when the mosquito feeds and enter the wound left by the proboscis. What is interesting about these microfilariae is that they exhibit a periodic cycle.