Comparative Survival of Hookworm Eggs and Strongyloides stercoralis First-Stage Larvae in Sludge From Septic Tanks

This study compares the survival of hookworm eggs and Strongyloides stercoralis first-stage larvae (L1) in septic tank sludge. Laboratory evidence suggests these helminths differ in survivability, but real-world data are lacking.

We enrolled 24 households, each with at least one member positive for S. stercoralis and at least one member positive for hookworm. Each member used their own household latrine for defecation. We collected stool samples from 112 individuals, followed by sludge sampling from 24 septic tanks 2 weeks later. Stool samples were examined using agar plate culture (APC) and a modified formalin-ether concentration technique (MFECT) to detect and count hookworm eggs, S. stercoralis L1, and other helminth eggs. In parallel, sludge samples were analysed using an APC method to detect hookworm third-stage larvae (L3) and S. stercoralis (L3 and free-living stages).

Hookworm L3 were positive in 48 sludge samples from 24 households collected from septic tanks of 24 latrines where hookworm-positive members defecated. In contrast, no S. stercoralis L3 or free-living males and females were found in 48 sludge samples from 24 septic tanks with S. stercoralis-positive household members defecating in latrines.

Hookworm eggs can survive in septic tank sludge, but S. stercoralis L1 cannot be detected using APC in 48 sludge samples. Thus, managing hookworm eggs in sludge is important, whereas special measures for S. stercoralis may not be needed. Using latrines effectively helps control strongyloidiasis.