Question

Filarial larva can be collected from man’s
A. Smears of intestinal contents
B. Peripheral blood at midnight
C. Smears of spleen
D. Biopsy of liver

Answer 1

Hint: Filariasis is caused by the worm Wuchereria bancrofti which is a member of phylum Nematoda and commonly called roundworms. These worms are parasitic in nature and depend on other organisms for food and nutrition. This worm needs two hosts to complete its life cycle- a vertebrate (primary host) and a secondary host which is an arthropod such as Culex fatigans(mosquito).
Complete step-by-step answer:
Wuchereria bancrofti in humans causes lymphatic filariasis. The larval phase of worms occurs in the arthropods. These larvae are transferred into the primary host through the mosquito bite. Once in the primary host, the reproductive cycle begins. Adult male and female worms are present in the lymphatic vessels of the body. The female worms here give rise to numerous, active, and microscopic embryos known as microfilariae. These microfilariae reside in the blood of the primary host. The female worms’ show circadian periodicity wherein, during the day the microfilariae are present in the deep veins and during the night they travel to the peripheral blood vessels. This circadian rhythm is maintained to ensure continuity of their life cycle, because most of the mosquitoes get their blood meal(s) from the vertebrates, when the latter are asleep or less active.
Hence, if we want to collect filarial larva from man then blood should be taken during the night i.e between 10pm to 4am because during this time period most of the microfilariae are present in the peripheral circulation.
Therefore, the correct answer is B- Peripheral blood at midnight.
Note: Wuchereria bancrofti causes filariasis which is commonly known as elephantiasis. It is transmitted due to a mosquito bite, which makes the mosquito a vector here. Mosquitoes commonly hover around the night for their blood meal from vertebrates and hence, such organisms like filarial worms which need mosquitoes for the completion of their life cycle are made available during the night so that they can be transferred to their intermediate host.