Q.Describe, with reference to each stage, the complete life cycle of Wuchereria bancrofti.
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Start your 14-day free trial to unlock the full solution →Wuchereria bancrofti is a digenetic parasite requiring two hosts to complete its life cycle: man, in whom the adult worms live and the microfilariae are produced, and the female Culex mosquito, inside which the larvae develop to the infective stage.
Stage 1: Uptake of microfilariae by the mosquito
The cycle begins when a female Culex mosquito bites an infected person at night and, while taking a blood meal, ingests circulating microfilariae — the sheathed, immature larval forms continuously released into the blood and lymph by adult female worms already established in that person. This timing is only possible because of nocturnal periodicity: although microfilariae remain in the deep blood vessels of internal organs (especially the lungs) during the day, they migrate into the peripheral circulation specifically at night, precisely when the night-biting Culex mosquito is feeding.
Stage 2: Development within the mosquito's thoracic muscles
Once inside the mosquito's stomach, the ingested microfilariae shed their sheath and actively penetrate the stomach wall, migrating to the mosquito's thoracic flight muscles. Here they develop in sequence through a first-stage larva, then a second-stage larva, and finally a third-stage larva.
Stage 3: The infective third-stage larva and migration to the proboscis
The third-stage larva is the infective form of the parasite. It migrates from the thoracic muscles to the mosquito's proboscis (the piercing-and-sucking mouthpart), where it remains positioned, ready to leave the mosquito's body during its next blood meal.
Stage 4: Transmission to a new human host
When this now-infective mosquito subsequently bites another person to take a blood meal, the third-stage larvae actively escape from the tip of the proboscis and enter the new host's body through the wound created by the bite, rather than being injected directly the way Plasmodium sporozoites are.
Stage 5: Migration to and establishment in the lymphatic system
Once inside the human host, the larvae migrate into the lymphatic vessels and lymph nodes, most commonly of the lower limbs and the external genital region. Over a period of several months, they undergo further development and moulting within the lymphatics, growing into mature adult worms.
Stage 6: Maturation, mating and release of microfilariae
The mature adult worms — long, thread-like (filiform) and coiled together within the lymphatic vessels — mate in situ. The female worm, which is longer and thicker than the male and is viviparous, then begins releasing large numbers of live, sheathed microfilariae directly into the surrounding lymph, from where they reach the general blood circulation. Once again showing nocturnal periodicity, these newly released microfilariae circulate in deep vessels by day and appear in the peripheral blood at night, ready to be picked up by a biting Culex mosquito, so completing and restarting the full cycle.
Pathogenicity linked to this cycle …
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