Results and Discussion
Clinical symptoms and pathological lesion s
General lethargy, reduced food intake, and loose stools were among the symptoms observed in the two pangolins examined in the present study. Furthermore, whereas electrolyte disturbance was observed, there was no evidence of leucopenia. The pangolins died naturally at 4-6 days post-rescue, with post-mortem examinations revealing apparent congestion and hemorrhage in the intestinal tract, thickened intestinal walls, and necrosis of the mucosal tissue (Fig. 1A). Histopathological observations, performed to determine lesions associated with CPV-induced diarrhea, revealed intensive injury to the mucosal layer of the small intestine to be a prominent feature, particularly the necrosis and shedding of intestinal mucosal intraepithelial cells and glands, which were observed in all parts of the small intestine (Fig. 1 B and C). Moreover, the submucosal layers were found to be characterized by inflammatory infiltrates, comprising primarily neutrophils and scattered lymphocytes. In addition, we observed a reduction in the number of lymphocytes in the spleen. The detection of bacteria in rectal tissues provided evidence to indicate the probable occurrence of secondary bacterial infection. In contrast, there was no indication of histopathological changes in the heart, liver, lungs, or kidneys.
Immunohistochemical analyses were performed to determine the localization of CPV antigen in the intestinal system of the CPV-infected pangolins, representative high-magnification images of which are presented in Fig 1. D and E. CPV antigens were detected in the duodenum, jejunum, and ileum, although not in the mesenteric lymph nodes, with strong HRP signals being observed in the crypt region and vicinity of inflamed cells. These pathological changes in CPV-infected pangolins are similar to those previously described in CPV-infected dogs, in which hemorrhagic enteritis and crypt neurosis are prominent features (Pollock, 1982).
Moreover, consistent with our observations of histopathological lesions, the crypt was established to be the major CPV antigen-positive region (Fig. 1). These pathological changes are consistent with those previously reported by Wang et al. (2020), thereby indicating that that CPV-2 targets and replicates within in the intestinal tract cells of animals in the order Pholidota.