Histological patterns in healing chronic wounds using Cochliomyia macellaria (Diptera: Calliphoridae) larvae and other therapeutic measures.

The healing process occurs due to the interaction of cellular, molecular, and biochemical events. Regarding lesions difficult to heal, especially in immunocompromised patients, monitoring and intervention to promote healing is a constant focus of research. Another aggravating factor is the increase in the number of reported cases of microbial resistance, indicating that various dressings and drugs have been increasingly inefficient. Larval therapy (LT) involves the application of sterile fly larvae on chronic and/or infected wounds, and it is an area emerging as an alternative therapy. Before the 1940s, the LT was widely used, but fell into disuse after the appearance of antibiotics. 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. However, many mechanisms of action of the larvae in this system remain poorly understood. Thus, the aim of the study was to investigate histopathological findings and to evaluate possible mechanisms of action of dipteran larvae during tissue repair. Lesions were induced in 24 male Wistar rats, to evaluate the effect of the type of treatment applied. The animals were divided into four groups: larval therapy (LT), LT associated with foam dressing with silver release (LTSIL), mechanical debridement and silver foam dressing (DEBSIL), and no treatment (CONT). Skin samples were collected for histopathological analysis. In LT, inflammatory response and angiogenesis were abundant; in LTSIL, inflammatory response with neutrophil infiltration was observed; in DEBSIL, scarce inflammatory response, small numbers of macrophages and lymphocytes, and bacterial colonization in depth; and in CONT, there was bacterial colonization in deeper tissues. The observed histological events show that the larvae had an important role in promoting the inflammatory response in the wound bed, drawing the essential immune cells for tissue reconstruction, and contributing to the inhibition of bacterial growth. However, more studies on the larval-host interactions are required for increasing the application of LT in the hospital routine.