Evaluation of the occurrence of inclusion cysts in the uterine serosa of capybaras (Hydrochoerus hydrochaeris)

Abstract

Capybaras (Hydrochoerus hydrochaeris), the largest rodents in the world, are prolific and live in structured social groups. These characteristics, combined with their role as hosts for the bacterium Rickettsia rickettsii, make them key targets in reproductive management strategies, particularly in endemic areas of Brazilian Spotted Fever (BSF). This study evaluated 140 female capybaras subjected to surgical sterilization during management campaigns. Findings include the identification of inclusion cysts in the uterine serosa, observed in 100 % of pluriparous individuals and absent in nulliparous ones. The cysts displayed histological characteristics consistent with reports in other species, consisting of a layer of cuboidal cells and an amorphous eosinophilic material. Hypotheses for their formation include lymphatic alterations, impaired venous return, and postpartum uterine contractions. The presence of cysts in the placenta and umbilical cord is unprecedented, suggesting a potential association with hormonal factors. Although benign, these cysts warrant attention to avoid misdiagnoses. It is concluded that multiparity is a determining factor in the formation of cysts in capybaras, while healthy nulliparous individuals did not present such alterations. The absence of studies on cysts in capybaras underscores the imperative need to continue investigations to refine population management and better 29 understand the clinical impacts of these findings.