Histopathological findings in wild Nutrias (Myocastor coypus) with Capillaria hepatica infection

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Capillaria hepatica is a zoonotic nematode that uses rodents and other mammals as hosts, especially rats and mice, and causes hepatic granuloma and eventually fibrosis/cirrhosis. However, C. hepatica infection in nutria, a large semiaquatic rodent, has rarely been reported, and histopathologic features of the infection have not been described in detail. We conducted necropsy on 36 wild nutrias. Some animals were found to have milky spots, parasitic eggs and worms within hepatic microgranuloma involving central calcification with cell debris, macrophages, eosinophils and multinucleated giant cells (MGCs). Interestingly, the eggs were closely surrounded by MGCs and appeared to be destroyed without inducing further chronic changes. Based on microscopical examination, C. hepatica infection was diagnosed, and we describe its histopathological characteristics in wild nutrias.