Pathological and morphometric characterization of intestinal lesions associated with natural infection by Oligacanthorhynchus microcephalus in white-eared opossums (Didelphis albiventris).

This retrospective study evaluated 29 free-living white-eared opossums (Didelphis albiventris) necropsied between 2022 and 2025. Among 19 adults, 13 (68.4%) presented intestinal remodeling associated with acanthocephalan (Oligacanthorhynchus microcephalus) attachment. Parasite burden was determined by counting attached individuals per animal, providing a measure of infection level. Macroscopically, firm nodules (3-11 mm) were observed, mainly in the jejunum, accompanied by luminal dilation and thinning of the intestinal wall. Histologically, the nodules involved mucosa, muscularis, and serosa, containing parasitic sections with necrosis, inflammatory infiltrate, and a thick collagenized capsule (mean 362 μm), with neovascularization; mineralization occurred in 36.4% cases. These findings demonstrate that O. microcephalus attachment induces focal chronic granulomatous inflammation and remodeling in D. albiventris. To our knowledge, this is the first detailed pathological and morphometric characterization of intestinal lesions caused by this parasite in this host species. Despite the retrospective design and relatively small sample size, the study provides novel insights into the dynamic progression of acanthocephalan-induced intestinal remodeling expanding comparative knowledge of acanthocephalan pathology in neotropical marsupials.