Evaluation of soil microfungi as biological control agents against ascarid eggs

Summary

Thick-shelled ascarid eggs have been reported to remain infective in the environment for several years, thus posing a prolonged risk of infection to animals and/or humans. The following in vitro study was therefore conducted to evaluate the negative impact of two species of naturally occuring soil microfungi (Pochonia chlamydosporia and Paecilomyces lilacinus), on the viability of Ascaridia galli, Toxocara canis and Ascaris suum eggs. Approximately 150 fresh eggs of individual ascarid species were embryonated on a 2% water agar in Petri dishes with or without a fungus (P. chlamydospria or P. lilacinus). On days 7, 14, 21, 28, 35 and 42 post experimental set up (p.s.), the viability of the eggs in each experimental group was evaluated (destructive sampling). By day 14 p.s., P. chlamydosporia had reduced the viability of A. galli and T. canis eggs by 70-86% and 52-67%, respectively, compared to the controls. In contrast, P. lilacinus had reduced the viability of A. galli and T. canis eggs by only 17-30% and 6-28%, respectively. Neither fungal species was found to be effective against A. suum eggs (<4% reduction in both cases). These results indicate interspecies differences in the susceptibility of ascarid eggs to microfungi. Ascaridia galli and T. canis eggs seemed to have been degenerated mainly due to hydrolysis of shells by fungal enzymes. The present study demonstrates that P. chlamydosporia may potentially be utilized as a biological control agent against A. galli and T. canis eggs in the environment.