https://phaidra.vetmeduni.ac.at/o:4558 Comparative pathogenesis of aerosol-induced colibacillosis reveals greater susceptibility in broiler chicks compared to layer chicks, with systemic clearance of bacteria but persistence in the bursa of Fabricius Rehman, Hammad Ur Hammad Ur Rehman 0000-0002-1135-7844 University of Veterinary Medicine Vienna Paudel, Surya Surya Paudel 0000-0002-4527-9733 University of Veterinary Medicine Vienna Hess, Claudia Claudia Hess 0000-0002-3535-5157 University of Veterinary Medicine Vienna Liebhart, Dieter Dieter Liebhart 0000-0003-2412-1248 University of Veterinary Medicine Vienna Bilic, Ivana Ivana Bilic 0000-0003-3296-5117 University of Veterinary Medicine Vienna Hess, Michael Michael Hess 0000-0002-6991-0120 University of Veterinary Medicine Vienna Abdelhamid, Mohamed Kamal Mohamed Kamal Abdelhamid 0000-0002-8136-9170 University of Veterinary Medicine Vienna Taylor & Francis Ltd journal article open access eng Avian colibacillosis presents significant challenges to the poultry industry by adversely affecting bird health and productivity and raising global public health concerns. While numerous studies on colibacillosis in broiler and layer chickens have been reported, a comparative investigation on the disease progression following respiratory infection in these two chicken types under identical conditions is lacking. This study aimed to compare the clinical, pathological, and microbiological features in broilers and layers experimentally infected with ilux2-marked E. coli PA14/17480/5-ovary strain (ilux2-APEC). Sixty-four 2-week-old specific pathogen-free chicks (32 broilers, 32 layers) were divided into four groups (n = 16), with control and infected groups for each type. Birds were necropsied at 3, 7, 10, and 14 days post-infection (dpi). In infected groups, spleen-to-body weight ratios were significantly higher compared to their respective controls. Mean maximum clinical scores, macroscopic, and microscopic lesions were significantly higher in infected broilers than in infected layers. Infected broilers showed a higher incidence of ilux2-APEC re-isolation from respiratory tissues compared to infected layers. Additionally, ilux2-APEC was re-isolated from blood, femoral head, heart, liver, and spleen exclusively in infected broilers. Unexpectedly, bioluminescence imaging identified bacterial colonization in the bursa of Fabricius in both infected groups, persisting up to 14 dpi. Immunohistochemistry detected Escherichia coli in trachea, lung, air sac, heart, liver spleen, and bursa of Fabricius, with higher detection rates in infected broilers. These findings highlight the increased susceptibility of broilers to APEC infection, suggesting a need for targeted disease control measures and potential genetic selection for improved disease resistance in broilers. Colibacillosis E.coli Broiler Layer ilux2-APEC Bursa Of Fabricius http://creativecommons.org/licenses/by-nc-nd/4.0/ https://phaidra.vetmeduni.ac.at/api/object/o:4558/download 10.1080/03079457.2025.2536331 https://phaidra.vetmeduni.ac.at/o:605 application/pdf Avian Pathology issn:1465-3338 VoR Avian Pathology 54 6 3.07 MB 2025