Listeria monocytogenes Infection in a Chicken (Gallus gallus domesticus): Pathology and Diagnostic Challenges

This case report details listeriosis in a chicken from a public botanic garden and the ancillary testing required to confirm Listeria monocytogenes. A 6-mo-old female Barred Plymouth Rock chicken, found deceased within its flock at a public botanic garden, was submitted to The Pennsylvania State University Animal Diagnostic Laboratory for postmortem examination. The clinical history included bloody feces, weight loss, and pallor prior to death. On postmortem examination, the chicken was emaciated with vent fecal staining. Gross lesions suggested bacterial septicemia, including necrotic fibrinous hepatitis, peritonitis, myocarditis, and pancreatitis. The heart was rounded, with pericardial effusion and a focal, dry, white bulging area around the left ventricle. Ulceration of the gizzard mucosa, severe, focal, unilateral cecal dilation, and ulceration with hemorrhage and necrosis were supportive of gastroenteritis and typhlitis. Differential diagnoses included lymphoid neoplasia, chronic coccidial or bacterial enteritis or typhlitis, bacterial septicemia, and mycobacteriosis. On histology, major findings included granulomatous myocarditis and endocarditis, as well as transmural coccidial enteritis and typhlitis. Preliminary results from ancillary testing confirmed severe coccidiosis and bacterial myocarditis. Although matrix-assisted laser desorption-ionization time of flight (MALDI-TOF) mass spectrometry identified nonpathogenic Listeria innocua, the severity of the heart lesions and the hemolysis observed on culture suggested a pathogenic species. Whole-genome sequencing confirmed the presence of L. monocytogenes, rather than the L. innocua incorrectly identified by MALDI-TOF. This case highlights the presentation of listeriosis in a chicken, the importance of confirmatory testing in the face of equivocal results, and potential disease risks in public spaces shared with avian species.