Methods for external disinfection of blow fly (Diptera: Calliphoridae) eggs prior to use in wound debridement therapy

Maggot debridement therapy (MDT) is the use of the larval stage of flies (i.e., Calliphoridae) to remove necrotic tissue and disinfect wounds. Effective MDT requires aseptic technique to prevent the unintentional introduction of pathogenic bacteria into a wound to be debrided; yet the external surface of Calliphoridae eggs is often heavily contaminated with bacteria. Studies of external disinfection of dipteran eggs have been reported, but neither their efficacy nor effect on egg viability has been adequately assessed. The present study evaluated the efficacy of ten disinfection techniques involving immersion, rinse, or a combination of both in formalin, Lysol, formaldehyde, bleach, ethanol, Sporgon, or benzalkonium chloride. All techniques resulted in significant decreases in culturable, aerobic bacterial load on Lucilia cuprina eggs. For L. cuprina, a 10 minute 3% Lysol immersion was the most efficacious, disinfecting 96.67% of egg samples, while resulting in 31.84% egg mortality. The 5% formalin immersion was least efficacious, disinfecting only 3.33% of L. cuprina egg samples, while resulting in 33.51% egg mortality. A formaldehyde immersion, one of the most commonly used disinfection techniques, was moderately effective, disinfecting 66.7% of egg samples, while resulting in 40.16% egg mortality. For Chrysomya rufifacies and Cochliomyia macellaria egg samples, the 10 minute 3% Lysol immersion disinfected 100% of the samples, and for Lucilia sericata, 80% of egg samples, while resulting in 33.97%, 7.34%, and 36.96% egg mortality, respectively. H2 CO disinfected 16.67% of Ch. rufifacies, 26.67% of C. macellaria, and 56.67% of L. sericata egg samples, while resulting in 21.98%, 10.18%, and 32.19% egg mortality, respectively. Due to its high disinfection efficacy and relatively low egg mortality, a 10 minutes 3% Lysol immersion is recommended for sterilizing Calliphoridae eggs prior to rearing of larvae for use in MDT.