Evaluation of larval density Cochliomyia macellaria F. (Diptera: Calliphoridae) for therapeutic use in the recovery of tegumentar injuries

Larval therapy (LT) is the application of carrion flies (Diptera) sterile larvae on chronic or infected wounds to promote or accelerate the healing process. High cost and the development of resistance by certain groups of pathogenic bacteria to these drugs encouraged the resurgence of LT, currently used in approximately 20 countries and more recently in Brazil. This study evaluated the behavior and larval density of Cochliomyia macellaria F. (Calliphoridae), one of the most appropriate species for debridement of injuries with necrotic tissue. Tegumentar lesions were induced in Wistar rats by subcutaneously application of 0.2 ml of a 1:4 hydrochloric acid and sterile distilled water in the dorsal region. Five experimental groups were set up: (LT 5) treatment with 5 larvae/cm²; (LT 15) 15 larvae/cm²; (LT 25) 25 larvae/cm²; (DEB) mechanical debridement, and (NUL) animals that did not receive any treatment. In the LT groups, larvae used were sterilized with sodium hypochlorite (NaClO) and maintained for 12 h in the lesions. The healing process was assessed qualitatively (macroscopically and microscopically) and quantitatively (time interval to complete healing). It was observed that the immature fed only on necrotic tissue, thus C. macellaria is an excellent candidate for use in LT. There was no significant difference in healing time between experimental groups. However, it was observed that in LT 25, there was greater vascularization in tissues when compared to the other treatments. The mechanisms involved in this process are unknown, but it is evident that the larvae have an important role in modulating the host immune response. It is essential that future applications of larval therapy consider using a higher density of larvae (minimum of 25 larvae/cm²) than is currently recommended.