Research on molecular epidemiology of aviadenovirus in Turkish commercial poultry flocks

1. Inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HHS) and adenoviral gizzard erosion (AGE) are poultry diseases that are caused by fowl aviadenovirus (FAdV). Identifying serotypes is crucial for differentiation.2. Between September 2020 and May 2021, 58 FAdV strains were isolated from 278 potentially infected commercial chicken flocks in Turkey, specifically from broiler and breeder flocks located in Balıkesir, İzmir, Manisa, Çanakkale, Afyonkarahisar, Bursa and Elazığ.3. Viruses were isolated from pooled internal organs and propagated using primary chicken embryo kidney cell cultures (CEKC) and SPF embryonated chicken eggs. Amplification by PCR of the <i>Hexon</i> gene, followed by Sanger sequencing, revealed three FAdV-D (serotype 11) and 55 FAdV-E (serotype 8b) genotypes.4. For next-generation sequencing (NGS), two representative serotypes, TR/FAdV/1 (FAdV-8b) and TR/FAdV/2 (FAdV-11) were chosen. Whole-genome sequencing performed on the Illumina MiSeq platform identified both as FAdV-8b. The TR/FAdV/1 genome, measuring 44 061 bp with a G/C content of 57.9%, showed 98.1% identity with the U.S. FAdV-E strain (GB624-U.S.A.). Meanwhile, the TR/FAdV/2 genome, consisting of 43 891 bp with a G/C content of 57.88%, displayed 99.90% similarity to the Spanish FAdV-E strain (11 -16 629). Both genomes contained 36 open reading frames (ORFs).5. Severe IBH outbreaks linked to FAdV-D and FAdV-E were marked by enlarged, pale yellow livers with petechial haemorrhages. At present, no commercial vaccines for FAdV are available locally. Understanding and characterising emerging FAdV strains is needed for vaccine development and control strategies.