Molecular Characterisation of Partial Structural Genes of Fowl Adenovirus Serotype 8b UPMT1901 Field Strain Isolate Associated with the Inclusion Body Hepatitis in Malaysia's Commercial Broiler Chickens

Fowl adenovirus (FAdV) is reported to pose a severe risk to the poultry industry, affecting food and nutrient security nationally and globally. FAdV is identified as the primary pathogen for inclusion body hepatitis (IBH) disease in avians during outbreaks in farms. Numerous interventions have been employed to reduce the chicken's mortality rate in future outbreaks, such as local autogenous vaccine production that has yet to be successfully commercialised. Fibre and hexon protein are two out of the three major components of the adenoviral capsid, identified to contribute towards FAdV virulence. Hence, this study aims to determine the fibre and hexon gene molecular changes of a local isolate, FAdV UPMT1901, in Malaysia's recent IBH outbreak and identify the evolutionary relationship with known FAdV strains. Propagation of FAdV UPMT1901 was performed in specific pathogen-free embryonated chicken prior to genomic extraction. The genes were amplified, and the retrieved nucleotide sequences were aligned with the published FAdV sequences. The phylogenetic tree analysis showed that UPMT1901 partial fibre and hexon genes are 99% similar to other known FAdV serotype 8b (FAdV-8b) species, especially the published Malaysian FAdV-8b isolates. Interestingly, the amino acid residue analysis further supported consistent residues amongst Malaysian isolates at fibre positions T176A, Q195H, D213E, S243T, A258V, F335Y, and F353V and hexon position T422M. These findings elucidate the structural proteins' functional capacity and molecular diversity, specifically amongst Malaysian FAdV isolates and FAdV-8b, while contributing to global initiatives to establish biosecurity, such as a vaccine or antiviral production against future outbreaks.