Paper II
Question
Lab diagnosis of filariasis caused by Brugia malayi
Answer
Laboratory diagnosis of filariasis caused by Brugia malayi:
- Peripheral blood smear microscopy — thick smear (Giemsa) for microfilariae, timed to nocturnal periodicity (blood collection around midnight, similar to W. bancrofti).
- Distinguishing microscopic features of B. malayi microfilariae: sheath present but stains poorly/does not take up Giemsa well (unlike W. bancrofti, whose sheath stains pink); body shows secondary kinks; longer cephalic space (length about twice the width); and, most distinctively, two separate, distinct terminal nuclei at the tail tip (versus a nuclei-free tail tip in W. bancrofti).
- Concentration techniques — Knott’s concentration method or membrane filtration, improving sensitivity.
- Circulating filarial antigen (CFA) test — primarily validated for W. bancrofti; less reliable/not standardly used for Brugia infections, which instead rely more on microscopy and antibody-based (Brugia-specific) tests where available.
- Ultrasonography — can visualize live adult worms within dilated lymphatics.
- Serology — supportive, limited specificity due to cross-reactivity.