Which causative filaria agent displays a nocturnal periodicity?

Appeared in: RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Explanation

Brugia malayi is a filarial nematode that causes lymphatic filariasis.
It exhibits nocturnal periodicity, meaning its microfilariae are found in the peripheral blood primarily at night.
This timing is synchronized with the biting habits of its mosquito vectors, mainly of the Mansonia and Anopheles genera.
This synchronization maximizes the chances of the microfilariae being ingested by a feeding mosquito, thus continuing the parasite's life cycle.

Option A: T. perstans, now known as Mansonella perstans, is characterized by its lack of a distinct 24-hour cycle. Its microfilariae are present in the blood at all times, a condition known as being non-periodic or aperiodic.
Option C: Although Brugia timori also exhibits nocturnal periodicity, it is a much less common cause of lymphatic filariasis and is geographically restricted to the islands of southeastern Indonesia. Brugia malayi is more widespread and a more common cause, making it the better answer.
Option D: Loa loa exhibits diurnal periodicity. Its microfilariae circulate in the peripheral blood during the daytime, which corresponds to the feeding habits of its vector, the Chrysops deerfly.

Visual 1: Diagram: Life cycle of Brugia malayi, highlighting the nocturnal migration of microfilariae to the peripheral blood and ingestion by a mosquito vector.
Visual 2: Chart: Comparison of periodicity among different filarial worms (Nocturnal, Diurnal, Subperiodic, Non-periodic) with examples for each.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Periodicity of Filarial Worms as background academic context rather than a clinical decision trigger.
Understanding filarial periodicity is crucial for accurate diagnosis. Blood samples for detecting microfilariae must be collected at the correct time of day based on the suspected species.
For suspected Brugia malayi or Wuchereria bancrofti infection, blood should be drawn at night (e.g., between 10 PM and 2 AM) to maximize the chance of finding microfilariae.
What if? If a blood sample for a patient with a classic Brugia malayi infection was drawn at noon, it would likely yield a false-negative result because the microfilariae would have retreated from the peripheral circulation into the deep tissues, primarily the lungs.

How to Approach the Question

First, identify the key terms in the question: 'filaria agent' and 'nocturnal periodicity'.
The question asks to identify which of the listed parasites has larvae (microfilariae) that are active in the blood at night.
Recall or look up the characteristics of the filarial worms listed in the options.
Evaluate each option: Loa loa is diurnal (day). T. perstans (Mansonella perstans) is non-periodic. Brugia timori is nocturnal, but less common.
Compare Brugia malayi and Brugia timori. Both are nocturnal. However, B. malayi is a more common and widespread cause of lymphatic filariasis, making it the most likely correct answer in an exam context.
Select Brugia malayi as the best fit for an agent with nocturnal periodicity.

Concept Tested & Keywords

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Practise the full RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Attempt every question from this paper in a timed mock, then review the full solution for each one.