Widespread Detection of Fowl Adenovirus Serotype 2/11 Species D Among Cases of Inclusion Body Hepatitis–Hydropericardium Syndrome in Chickens in Egypt

Fowl adenoviruses (FAdVs) are important emerging pathogens affecting the poultry industry in Egypt as they are the primary etiology of inclusion body hepatitis–hydropericardium syndrome (IBH-HPS) associated with severe economic losses. This study aims to identify the circulating FAdVs from cases of IBH-HPS in 5 Egyptian provinces during the period from October 2020 through September 2022. Out of the 210 examined flocks, liver samples from 66 flocks were positive for FAdVs (31.4%) using conventional polymerase chain reaction targeting loop 1 of the major hexon gene, with varying rates of mortality (1% to 14%). In the positive samples detected during the study, the histopathological examination revealed pathognomonic lesions of FAdVs, including basophilic and eosinophilic intra-nuclear inclusion bodies (INIBs). The percentage of FAdV positivity increased with the flock age; from samples collected at ages 1 to10, 11 to 20, 21 to 30, and >30 days of age, 10% (5/50), 25.6% (11/43), 34.3% (23/67), and 54% (27/50) were found positive for FAdVs, respectively. Notably, the positivity percentages among the flocks reared in cages were higher than for those reared in the deep litter system of housing. The gene sequencing and phylogenetic analysis of 19 strains revealed clustering into FAdV species D serotype 2/11, demonstrating that serotype 2/11 is most prevalent in the targeted Egyptian provinces during the period of the study. Several point mutations in the sequenced region among different strains were reported. These findings underscore the prevalence of FAdV and provide a basis for further research on circulating strains to develop effective control strategies.