Fowl adenovirus infection and inclusion body hepatitis in Canada: genotyping trends from 2008 to 2024.

Between 2008 and 2024, fowl adenovirus (FAdV) genotypes were determined by hexon gene sequencing for 1,362 samples: 1,234 from 9 Canadian provinces and 128 samples from the United States. Most genotyped samples were from Ontario (681), followed by Alberta (243), Nova Scotia (116), British Columbia (77), Quebec (58), Saskatchewan (21), Manitoba (20), Newfoundland (16), and Prince Edward Island (2). Most samples (1,285) were related to inclusion body hepatitis (IBH); 77 samples were submitted for other reasons. Four FAdV genotypes (FAdV2, FAdV8a, FAdV8b, FAdV11) were associated with IBH-related submissions. Between 2008 and 2014, the most common strains associated with IBH outbreaks were FAdV11 and FAdV8a. However, since 2015, the identity of FAdVs involved in IBH outbreaks has shifted, with FAdV8b becoming the most frequent IBH-associated strain, largely displacing FAdV8a and FAdV11. In a much smaller group of 77 samples from non-IBH submissions, 10 FAdV genotypes were detected: FAdV1, FAdV2, FAdV3, FAdV4, FAdV6, FAdV7, FAdV8a, FAdV8b, FAdV9, and FAdV11. Although FAdV4 is a recognized causative agent of hepatitis-hydropericardium syndrome worldwide, no association with clinical disease was reported in the birds included in our study. Our comprehensive 17-y analysis of FAdV circulation patterns will support the development of control measures and vaccination programs to reduce the impact of FAdV-related outbreaks.