Beatrice Grafl (Clinical Centre for Population Medicine in Fish, Pig and Poultry, Clinical Department for Farm Animals and Food System Transformation, Departments, University of Veterinary Medicine Vienna) Beatrice Grafl Peter Mitsch Peter Mitsch Ernst Wiesinger Ernst Wiesinger Josef Ziegerhofer Josef Ziegerhofer Ivana Bilic (Clinical Centre for Population Medicine in Fish, Pig and Poultry, Clinical Department for Farm Animals and Food System Transformation, Departments, University of Veterinary Medicine Vienna) Ivana Bilic Claudia Hess (Clinical Centre for Population Medicine in Fish, Pig and Poultry, Clinical Department for Farm Animals and Food System Transformation, Departments, University of Veterinary Medicine Vienna) Claudia Hess Dieter Liebhart (Clinical Centre for Population Medicine in Fish, Pig and Poultry, Clinical Department for Farm Animals and Food System Transformation, Departments, University of Veterinary Medicine Vienna) Dieter Liebhart Michael Hess (Clinical Centre for Population Medicine in Fish, Pig and Poultry, Clinical Department for Farm Animals and Food System Transformation, Departments, University of Veterinary Medicine Vienna) Michael Hess MDPI 2026 In recent years, outbreaks of inclusion body hepatitis (IBH) have been reported with increasing frequency worldwide. In Austria, the presence of fowl aviadenoviruses (FAdVs) and/or IBH has been documented sporadically. The present report describes a surge of natural IBH cases in fifteen Ross 308 broiler flocks. The clinical picture was characterized by the sudden onset of increased mortality in birds 3 to 15 days of age, persisting for approximately one week, resulting in cumulative flock mortality ranging from 2% to 27%. The main pathological findings were hepatitis with diffuse necrotic foci and petechial hemorrhages with intranuclear inclusion bodies by histology. FAdV was detected in liver samples from all affected flocks. Based upon partial hexon sequence analysis, FAdV serotype-11, species-D (FAdV-11, FAdV-D) was identified, showing complete sequence identity among broiler-derived strains and high identity with previous isolates from Austria and globally IBH-associated isolates. Furthermore, FAdV-11 DNA was detected in dead-in-shell embryos collected during the ongoing outbreak, originating from one suspect broiler breeder flock, confirming vertical transmission. Serological investigations of the suspect breeders confirmed the FAdV-11 infections within the studied timeframe. In conclusion, investigations confirmed vertical transmission of FAdV-11 and subsequent manifestation of IBH in broilers under field conditions, highlighting the epidemiological importance of broiler breeders in IBH outbreaks. PDFDocument eng 2026-10-09T08:18:36.328726986Z 2026 inclusion body hepatitis fowl adenovirus serotype 11 broiler broiler breeder vertical transmission mortality 3010830 b application/pdf http://creativecommons.org/licenses/by/4.0/