Why is sampling timed to night hours for nocturnally periodic microfilariae such as Wuchereria bancrofti?

• A. Microfilariae display nocturnal periodicity; sampling at night improves sensitivity
• B. Microfilariae circulate only in daytime
• C. Microfilariae are only present in urine at night
• D. Microfilariae peak in the afternoon

Answer: (D)

Nocturnal periodicity means the microfilariae of Wuchereria bancrofti cycle in and out of peripheral blood over a 24-hour day, appearing in higher numbers at night. Sampling during those hours catches the parasites when they are most abundant in the bloodstream, which makes microscopic detection more likely and thus increases test sensitivity. This timing matches the parasite’s strategy to align with the mosquito vectors that feed at night, enhancing transmission.

The other ideas don’t fit the biology: these microfilariae do not circulate only in daytime, they aren’t confined to urine, and their peak in the bloodstream is at night—not in the afternoon.