ASCARIS SUUM EGG RECOVERY FROM SLUDGE SAMPLES AFTER PHASE EXTRACTION

Some helminth test methods for sanitation samples include a phase extraction step to reduce lipid content and final pellet size before microscopy. Hydrophilic and lipophilic solutions are used to create 2 phases, with a plug of organic material or debris in between, whilst eggs are supposedly compacted at the bottom of the test tube. We tested 10% formalin, acetoacetic buffer, and acid alcohol as the hydrophilic solutions, and ethyl acetate and diethyl ether as the lipophilic solvents for egg recoverability from water, primary sludge, and fatty sludge. Normally, the supernatant and debris plug are discarded and the sedimented pellet of eggs is microscopically examined. We, however, also collected the entire supernatant plus debris plug to determine where eggs were possibly lost. We found that eggs were lost when samples were extracted with 10% formalin + ethyl acetate, 10% formalin + diethyl ether, acetoacetic buffer + ethyl acetate, and acetoacetic buffer + diethyl ether combinations (<50% egg recovery). Acid alcohol + ethyl acetate resulted in 93.2, 89.8, and 57.3% egg recovery in the pellet of water, primary sludge, and fatty sludge, respectively; however, the size of the final pellet was not reduced, defeating the purpose of the extraction step. We thus recommend that this step be excluded.