Comparative Effect of Water-Diluted Stool on the Growth and Development of Rhabditis sp., Strongyloides stercoralis, and Hookworm.

Abstract

Background: Raw vegetables in southern Thailand frequently carry Rhabditis sp. Epidemiological shifts (2008-2023) show an increase in Rhabditis sp. colonization alongside declining hookworm and Strongyloides stercoralis infections, suggesting a potential association with climate variations. To evaluate moisture effects under controlled conditions, we compared nematode egg and first-stage larval development using an agar plate culture (APC) control and a 1:20 water-diluted stool suspension (SS) simulating wet environments.

Methods: Stool samples positive for Rhabditis sp. from 18 humans (12 co-infected with hookworm or S. stercoralis) and 25 dogs (10 co-infected with hookworm) were cultured concurrently in APC and SS. Following a 6-day incubation at room temperature, we quantified Rhabditis sp. developmental stages and third-stage larvae (L3) of hookworm and S. stercoralis.

Results: In APC, all human (18/18) and dog (25/25) cases achieved complete Rhabditis sp. development, supporting significantly more developmental stages than SS. In SS, only 22.2% of human and 28.0% of dog cases exhibited partial development, confirming that water dilution impairs Rhabditis sp. growth. Conversely, hookworms reached the L3 stage in all human (8/8) and dog (10/10) cases across both methods without significant differences. For S. stercoralis (7/7 humans), both methods yielded L3, though APC provided higher yields.

Conclusions: Our experimental findings demonstrate that Rhabditis sp. development is significantly more vulnerable to water dilution than hookworm or S. stercoralis. While this impairment is hypothesized to stem from reduced bacterial abundance, this mechanism remains speculative and requires direct microbiological confirmation. These laboratory observations suggest that lower-moisture environments may favor Rhabditis sp. developmental success over other nematodes, though broader ecological and epidemiological implications require further study given the limited sample size.