In lymphatic filariasis caused by Wuchereria bancrofti, microfilariae exhibit nocturnal periodicity (accumulate in peripheral blood at night). The recommended diagnostic technique and optimal timing for blood sample collection is:

• A Thick blood smear collected at noon; Giemsa stain
• B Day-time antigen detection by immunochromatographic card test (ICT)
• C Thick blood smear collected between 10 PM and 2 AM; Giemsa stain ✓
• D Night blood smear is required only for Brugia malayi, not W. bancrofti

Explanation

W. bancrofti microfilariae in most regions (especially India) show nocturnal periodicity — they accumulate in pulmonary capillaries during the day and appear in peripheral blood primarily between 10 PM and 2 AM. Thick blood smears stained with Giemsa or haematoxylin must be prepared from blood collected during this window for maximum sensitivity. The immunochromatographic card test (ICT) / Filariasis Ag card test detects W. bancrofti circulating filarial antigen (CFA) in day-time blood samples and is WHO-recommended for surveillance — it does not require night blood collection.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.