Third stage larva of Wuchereria bancrofti carried by Culex mosquito is called
(a) Cysticercus
(b) Merozoite
(c) Microfilariae
(d) Trophozoite

Hint: This larva is sheathed and has nocturnal periodicity, except the South Pacific microfilaria which does not have marked periodicity. It has a gently curved body and a tail that's tapered to some extent.

Complete step by step answer:
- A microfilaria is about $240 \ \mu m - 300 \ \mu m$ long and $7.5 \ \mu m - 10 \ \mu m$ thick.
- The nuclear column that is the cells that constitute its body is loosely packed.
- The cells are often seen individually under a microscope and don't reach the tip of the tail.
- Infective larvae are transmitted by infected biting mosquitoes during a feed.
- Inside the mosquito, the microfilariae develop within 1 to 2 weeks into infective filariform third-stage larvae.
- During a subsequent feed by the mosquito, the larvae infect the human host.
- They migrate to the lymphatic vessels and lymph nodes of the human host, where they become adults.
- The larvae migrate to lymphatic vessels and lymph nodes, where they become microfilariae-producing adults.
- Adult female worms produce microfilariae.
- Feeding vector mosquitoes ingest microfilariae from the bloodstream.
- In the mosquito, the microfilariae mature into infective larvae, which migrate to the mosquito's mouthparts, enter a replacement host via the vector's puncture wound, migrate to the lymphatics, mature, and finally mate to produce more infective larvae.
- The eight different microfilariae are often classified counting on their habitat in human tissues. The microfilariae nematodes which parasitize man contains the following:
Wuchereria bancrofti
Brugia malayi
Brugia timori
Loa loa
Onchocerca volvulus
Mansonella perstans
Mansonella streptocerca
Dipetalonema streptocerca.
So, the correct answer is, ‘Microfilariae.’

Note:
- Nocturnal periodicity: The worms can only be detected within the blood of these infected around the hour of midnight.
- New specific card test: Test which detects parasites by using only finger- prick blood tests any time of day. Ultrasound can identify rapidly moving adult worms.
- Antigen detection: Circulating filarial antigen (CFA) - 'gold standard' for diagnosing Wuchereria bancrofti infections in the sample.