THE EFFECTS OF TECHNICAL STEPS USED IN EXISTING SANITATION HELMINTH TEST METHODS ON ASCARIS SUUM EGG RECOVERY FROM PIG FECES

Abstract

Many technical aspects are associated with helminth egg isolation and enumeration that affect how efficiently eggs are recovered from samples. This study investigated Ascaris egg recoverability when samples were washed with or without pressure, and from different sample types (water, effluent, ventilated improved pit latrine [VIP], urine diversion dry toilet [UDDT], dried, fatty, and septic tank sludges, and soil) when processed with water, ammonium bicarbonate, and 7X®. We also looked at egg recovery after flotation with zinc sulfate, magnesium sulfate, and sodium nitrate at specific gravities of 1.18, 1.2, and 1.3, at respective centrifugation speeds and times after washing (1,050 and 1,512 g for 5, 10, and 15 min) and after flotation (672 and 1,050 g for 5, 10, and 15 min). We found that samples should be washed under pressure to ensure full dissociation of eggs from the sample matrix and then centrifuged at 1,512 g for 10 min. For sludge samples (or samples with high-fat content), 7X produced the best egg recovery and clearest samples for microscopic analysis, while soil and soil-containing (UDDT sludge) samples were best processed with ammonium bicarbonate. Flotation was optimal with zinc sulfate at a specific gravity of 1.3 after centrifugation at 672 g for 15 min.

Keywords: Centrifugation; Egg recovery; Flotation; Helminth eggs; Sample type; Specific gravity; Wash solution.