Wuchereria bancrofti microfilariae exhibit nocturnal periodicity in blood. This periodicity is explained by which physiological mechanism?

• A Microfilariae actively migrate from lymphatics to peripheral blood in response to nocturnal fall in core body temperature
• B The adult female worm releases microfilariae only during nighttime under circadian hormonal influence of melatonin
• C Microfilariae are destroyed by daytime fever and replenished from lymphatic reservoirs at night
• D Microfilariae accumulate in pulmonary capillaries during the day and are released into peripheral circulation at night due to a change in host posture and oxygen tension ✓

Explanation

Nocturnal periodicity of W. bancrofti microfilariae is explained by the 'lung accumulation' theory: during the day, microfilariae sequester in the pulmonary capillaries (high oxygen environment daytime lung blood flow); at night, when the host is recumbent, the change in posture reduces pulmonary capillary oxygen tension and blood flow differences, causing microfilariae to redistribute into peripheral blood. This matches the feeding habits of the night-biting Culex mosquito vector. The adult worm does not selectively release microfilariae at night, and melatonin control is not established as the direct mechanism.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.