Abstract
Avian infective endocarditis is an uncommon but severe disease that is typically diagnosed postmortem because of nonspecific clinical signs and rapid progression. In the present study, five broiler chickens (n = 5) from a commercial flock were examined with septicemia and lesions suggestive of endocarditis. This study reports the first molecularly confirmed and characterized case of valvular endocarditis associated with multidrug-resistant Vagococcus fluvialis in poultry and provides a comprehensive review of bacterial endocarditis in avian species. The case involved a broiler chicken that presented with sudden death and septicemic lesions, including vegetative valvular endocarditis, pericarditis, and multiorgan involvement. Bacterial isolates recovered from cardiac lesions were identified as V. fluvialis using MALDI-TOF mass spectrometry and confirmed by 16S rRNA gene sequencing. Antimicrobial susceptibility testing revealed a multidrug resistance profile, with resistance to several antimicrobial classes commonly used in poultry production. The literature review identified published studies describing avian infective endocarditis, which predominantly affects poultry and is caused mainly by Gram-positive bacteria, with clinical signs and necropsy findings largely overlapping across etiologies. These findings highlight the novelty of V. fluvialis as a potential etiological agent of avian infective endocarditis and underscores the diagnostic challenges associated with avian endocarditis, particularly when uncommon pathogens are involved, and underscore the importance of advanced identification methods for an accurate etiological determination. Collectively, the results of this study expand the spectrum of bacterial species associated with avian infective endocarditis and emphasize the relevance of antimicrobial resistance and improved diagnostic strategies in poultry health and disease surveillance.