Experimentally induced lesions of an emerging pathogenic strain of Salmonella Gallinarum in broiler chicks

An emerging highly pathogenic strain of Salmonella Gallinarum biovar Gallinarum (SG) was isolated from a severe natural outbreak of fowl typhoid, with enteric and systemic lesions, and used for the infection of broiler chicks. This strain was genetically characterized by a greater diversity of virulence and antimicrobial resistance genes. A total of 160 1-day-old Ross broiler chicks were divided into four groups and received oral and intranasal inoculations of SG at different cell concentrations. From 3-12 days post-inoculation, postmortem examinations were performed on the chicks to collect samples for bacteriological, histopathological, and immunohistochemical examinations. Typical gross and histological lesions such as fibrinonecrotic and/or histiocytic hepatitis, splenitis, and myocarditis were found in chicks from all groups. Unexpected lesions included marked transmural and non-transmural histiocytic enteritis, laryngitis and tracheitis, interstitial pneumonia and glomerulonephritis, glomerular thrombosis, fibrinous and histiocytic bone marrow myelitis, necrotic and histiocytic bursitis, and necrotic and histiocytic encephalitis. Within lesions, SG was detected by immunohistochemistry in all affected tissues, as well as by retrieval of the pathogen from liver and spleen in bacteriology. Intranasally challenged chicks had more pathogenic presentation of the disease changes, compared to orally challenged chicks, with a greater number of affected organs and intestinal segments. These results highlight the importance of the respiratory route for the pathogenesis of the infection and disease. An emerging highly virulent S. Gallinarum strain caused uncommon respiratory and intestinal lesions.The intranasal route of challenge caused a more severe and systemic disease, with broader organ involvement.The emerging strain targeted novel organs including larynx, trachea, bursa of Fabricius, and bone marrow. An emerging highly virulent S. Gallinarum strain caused uncommon respiratory and intestinal lesions. The intranasal route of challenge caused a more severe and systemic disease, with broader organ involvement. The emerging strain targeted novel organs including larynx, trachea, bursa of Fabricius, and bone marrow.