Peripheral Blood Smear (PS) for Microfilaria

A Peripheral Blood Smear (PS) is a microscopic examination of blood to detect microfilariae, which are the larval stage of filarial parasites like:

• Wuchereria bancrofti (most common cause of lymphatic filariasis)
• Brugia malayi
• Loa loa
• Onchocerca volvulus

Key Points About Microfilaria Testing

• Sample Collection:
  • Usually collected at night (10 PM – 2 AM) because microfilariae exhibit nocturnal periodicity (they are more present in peripheral blood at night).
  • Some species, like Loa loa, show diurnal periodicity (more present during the day).
• Staining: Giemsa or Wright’s stain is used for visualization under a microscope.
• Appearance: Microfilariae appear as slender, thread-like organisms in the blood smear.
• Alternative Tests:
  • Thick and thin blood smears
  • Knott’s concentration test
  • Serological tests (ELISA, PCR) for better sensitivity