Paper II
Question
Microfilaria of Loa-Loa
Answer
Microfilaria of Loa loa — the larval stage of the African “eye worm” — shows characteristic morphological features distinguishing it from Wuchereria bancrofti and Brugia malayi:
- Sheath: present, but does not stain with Giemsa (unlike W. bancrofti, whose sheath stains pink).
- Nuclear column: the somatic nuclei extend all the way to the tip of the tail — a key distinguishing feature from both W. bancrofti (nuclei-free tail tip) and B. malayi (two distinct terminal nuclei).
- Periodicity: shows diurnal periodicity — peak microfilarial density in peripheral blood during the daytime, matching the day-biting habit of its vector, the Chrysops fly (deer/mango fly).
Clinical correlation: Loa loa adult worms migrate through subcutaneous tissue, causing transient, localized subcutaneous swellings (“Calabar swellings”), and are occasionally directly visible migrating across the subconjunctiva of the eye (“eye worm”).
Laboratory diagnosis: peripheral blood smear (thick smear, Giemsa), collected during the daytime given diurnal periodicity — the opposite timing to W. bancrofti blood collection.