Sodium Hypochlorite: Optimization of Application as an Exsheathing Agent for Nematode Larvae to Minimize the Risk of Reduced Viability

Objective: Nematode larvae exsheathing is a crucial procedure employed in experimental studies such as nematode viability assays, evaluating nematodes' resistance to anthelmintics, and evaluating the efficacy of anthelmintic medications. The exsheathment procedure allows for quantifying the direct impact on larvae when the protective sheath is removed. Sodium hypochlorite (NaOCl) is a commonly used artificial exsheathment medium. However, concerns have been raised about its potential impact on the viability of exsheathed larvae. A previous study utilized Strongyloides papillosus larvae, a nematode species without a protective sheath, to investigate the effects of NaOCl on parasite viability. The findings revealed that there are specific concentration (C) and exposure-time (T) thresholds (0.3% > C > 0.2%; 10 min > T > 5 min) beyond which viability decreases, and excessive exposure can cause significant damage. The current study aims to determine the optimal concentration of NaOCl that can induce exsheathment in ensheathed-type larvae without compromising their viability. Methods: Third-stage strongylid larvae of donkey origin were utilized for this study, with chemical concentrations of 3%, 0.3%, 0.2%, 0.1%, or 0.05%. Larval motility served as the criterion for evaluating viability. Results: NaOCl can exsheath larvae at any of the five concentration levels evaluated, depending on the duration of exposure to the compound. A concentration of 0.2% is considered optimal, inducing exsheathment as early as 2 minutes. Extended exposure for up to 10 minutes did not impact larval viability. A 3% solution causes larval damage. Conclusions: Regarding the effect of NaOCl on nematode larvae, the results validate the earlier findings with Strongyloides papillosus and those by other authors employing nematodes such as Haemonchus contortus and Cooperia curticei, and the entomopathogenic nematode Heterorhabditis bacteriophora.