SUMMARY. Trueperella pyogenes is an opportunistic Gram-positive bacterium that induces purulent lesions and abscesses in cattle, small ruminants and swine. In birds, T. pyogenes infections have been linked to lameness and osteomyelitis in turkeys and hepatic fibriscess in turkeys and pigeons. An 18-month-old backyard rooster with a history of progressive emaciation was submitted to the California Animal Health and Food Safety (CAHFS) laboratory system. At necropsy, unusual numerous miliary granulomas were identified primarily in the spleen, but granulomas were also observed in air sacs and lungs. Microscopically, few to moderate numbers of granulomas with giant cells were observed in the spleen, lung, air sacs and crop, composed of necrosis and mixed inflammatory cell inflammation, including multinucleated giant cells, fibrin deposition and fibrosis.  T. pyogenes was isolated from the air sacs and trachea. Avibacterium paragallinarum PCR was positive from the tracheal swab.  A retrospective analysis of CAHFS data on Trueperella pyogenes between 2000 and 2020 identified 24 cases in avian species: chickens (16/24), turkeys (5/24), Pekin duck (1/24), parrot (1/24) and pheasant (1/24). Although T. pyogenes infection in birds is rare, the clinical signs and gross lesions might be indistinguishable from avian mycobacteriosis in some cases and should be considered in the differential diagnosis.

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