M L R Delgado, C da Silva Ribeiro, L A Anjos
Anuran amphibians play essential ecological roles and are considered important bioindicators. This is especially true during the larval stage, when tadpoles exhibit high sensitivity to parasitic infections, including trematode metacercariae. These infections can profoundly affect the physiology and morphology of juvenile hosts, potentially compromising tissues involved in osmoregulation, locomotion, and development. We analysed naturally infected tadpoles, performing parasitological screening and histopathological evaluation. Through field collection, euthanasia, histological processing, and microscopic analysis of the tissues, our results revealed that the presence of metacercariae is directly associated with progressive tissue damage. In the kidneys, after the establishment of the parasite in a previously healthy renal tubule, we observed alterations ranging from mild changes, such as a slight reduction in glomerular density in individuals with low infection intensity, to severe damage in highly infected individuals. In the tail musculature, the metacercariae were encapsulated between muscle bundles, forming cysts delimited by fibrous capsules, accompanied by alterations in the organisation of muscle fibres, disruption of connective tissue, and the presence of inflammatory infiltrate. Capsules surrounding the parasites were composed of both host tissues and parasite-derived structures. Their formation was frequently associated with necrotic areas and functional impairment. These findings demonstrate that trematode infection exerts progressive effects on the structure and morphology of renal and muscular tissues in tadpoles, with the severity of tissue damage increasing according to parasite infection intensity. Such alterations may compromise host tissue integrity and represent an important pathological consequence of natural trematode infections during the larval stage.