A night blood film shows sheathed microfilariae in a patient with episodic lymphangitis. Close study of the stained tail shows that the column of nuclei stops short of the tail tip, but two distinct nuclei are present separately at the extreme tip. Which filarial worm is identified?

• A Brugia malayi ✓
• B Wuchereria bancrofti
• C Loa loa
• D Mansonella perstans

Explanation

Sheathed microfilariae occur in Wuchereria bancrofti, Brugia malayi, Brugia timori, and Loa loa, whereas Mansonella species are unsheathed, eliminating option D. Species are separated by the tail: in W. bancrofti the nuclei stop short, leaving the tail tip entirely free of nuclei, in B. malayi two discrete terminal nuclei sit at the tail tip separated from the main nuclear column, and in L. loa nuclei run continuously to the tip. Periodicity cannot distinguish them since both W. bancrofti and the nocturnal strain of B. malayi show night periodicity.

Reference: Paniker's Textbook of Medical Parasitology, 8th ed.

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