Frequent Development of Inflammatory Lesions and Lymphoid Foci in the Kidneys of Japanese Wild Crows (Corvus macrorhynchos and Corvus corone) as a Result of the Entry of Causal Agents via the Renal Portal Blood

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Although the increase in the number of wild crows is causing social problems in urban areas, crows play an increasingly important role in monitoring serious infectious diseases, such as highly pathogenic avian influenza and West Nile fever. To gain a better understanding of normal conditions and common disorders in crows, we conducted a retrospective study of wild crows captured in central Japan in the 1990s and examined the necropsy findings from 166 jungle crows (Corvus macrorhynchos) and 74 carrion crows (Corvus corone). We found frequent development of lymphoid foci and inflammatory lesions in the kidneys of both species of crows. These findings were unrelated to place or date of capture, indicating the universality of renal lesion developments in the Corvus species. In the kidneys, suppurative granulomas were concentrated in the renal cortex and the vein wall, indicating the haematoegenous spread of causal agents. However, the glomeruli remained intact, unlike the spreading of causal agents via arterial blood, which strongly suggested the renal portal blood as a possible entry route of causal agents. The renal lymphoid foci showed the same distribution as the granulomas, supporting the possibility of external agents entering through renal portal blood. We also identified types of parasites in Japanese wild crows by means of histopathological analysis. We hope that our data will contribute to the appropriate evaluation and a better understanding of pathological conditions in Japanese wild crows.