Pyogranulomatous pneumonia associated with Actinomyces hyovaginalis infection in a free-ranging Brazilian wild boar

Abstract

Actinomyces (A.) hyovaginalis is a Gram-positive, rod-shaped, polymorphic bacterium. In domestic pigs, the infection is typically associated with pyogranulomatous pneumonia. In wild boars, this infection was never associated with such lesion. We report the gross, histopathological, and bacteriological findings in a case of pyogranulomatous pneumonia caused by A. hyovaginalis infection in a free-ranging wild boar. Fragments of the lungs, lymph nodes, and heart from a wild boar were sent by boar hunters for histopathological analysis with a presumptive tuberculosis diagnosis. Grossly, in the lungs, there were multiple nodules of 0.1 to 0.8 cm in diameter, with light-yellow, opaque, friable necrotic centers. Histologically, these nodules were composed of coagulative necrosis, with abundant amorphous to granular eosinophilic material, neutrophilic inflammatory infiltrate, cellular debris, multifocal mineralization, and numerous intralesional extracellular coccobacillary basophilic bacterial colonies within the necrotic centers. Surrounding these areas, there were concentric layers of a marked inflammatory infiltrate of lymphocytes, plasma cells, macrophages, epithelioid macrophages, and neutrophils. The Brown-Hopps stain evidenced intralesional Gram-positive bacilli. In bacterial culture, small white partial hemolytic colonies were identified in 5% blood sheep agar. The isolated bacterium was identified as A. hyovaginalis by MALDI-TOF MS. Based on the gross, histopathological, and bacteriological findings, a diagnosis of pyogranulomatous pneumonia by A. hyovaginalis was established. Although not previously reported in this suid species, this infection should be considered a differential diagnosis for pyogranulomatous pulmonary lesions in wild boars.

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