Pathological Findings of Nestling European Goldfinches () Co-Infected with and .

Bacterial diseases are widespread in pet birds, posing a severe threat in nestlings and birds with weakened immune systems, often resulting in high mortality during the first days after hatching. This study aimed to describe the pathological findings of a natural bacterial co-infection with and in nestling European goldfinches (), as a cause of mortality after hatching. Eight nestlings kept in a breeding facility showed an inability to move, anorexia, and respiratory distress, and were found dead between 1 and 4 days of life. Gross pathological findings included diffuse pneumonia with edema and multifocal hemorrhages and occasionally hepatic necrosis. On histopathology, the main findings in all examined birds included severe, subacute bronchopneumonia and severe necrotizing hepatitis. Gram-negative bacilli were observed in parabronchial walls, within pulmonary arteries and surrounding hepatocellular necrotic foci. Lungs, livers and kidneys were sampled for bacteriological examination, resulting in two Gram-negative bacterial isolates. Four housekeeping genes (i.e., 16S rRNA; ; ; ) were amplified and sequenced for bacterial identification at species level. Although and are common Gram-negative pathogens and are often co-isolated in human bacterial pneumonia, co-infection with these bacteria has not been documented in nestling goldfinches to date. Pathogen identification is essential for formulating a correct etiological diagnosis and further selecting the most appropriate therapeutic strategy.