Abstract
Background:
Avian nephritis virus (ANV) infections in commercial broiler flocks cause gastroenteritis and renal diseases, leading to economic losses in the poultry industry.

Aim:
To determine the genetic diversity of ANV strains by analyzing the ORF2 gene sequences.

Methods:
A total of 140 suspected samples of ANV were isolated from broiler chickens collected in Ben Tre Province, Vietnam, between 2024 and 2025. Molecular diagnosis was performed using real-time RT-PCR, and positive samples were subsequently sequenced. The obtained sequences were compared with reference ANV strains in GenBank to assess genetic similarity, variation, and recombination.

Results:
Overall, 24/140 (17.14%) samples were positive for ANV. Two ANV strains, referred to as ANV-ORF2-MK3 (PV872384) and ANV-ORF2-MK4 (PV872385), were sequenced. Phylogenetic analysis revealed that the ANV-ORF2-MK3 (PV872384) and ANV-ORF2-MK4 (PV872385) strains were clustered with Avian AstV Brazil 5-3 (KU711052), ANV-VF08-53 (HQ330499), and RS/BR/15/6R (MG846415) strains. Both strains showed high nucleotide and amino acid sequence identity with ANV-VF08-53 (nucleotide: 75.63% and 75.52%; amino acid: 76.06% and 75.90%, respectively), and genotype 8 was identified. Additionally, amino acid sequence analysis of the isolated strains compared with reference strains indicated substantial variability, particularly in regions 416–424, 448–489, and 558–566. A recombination signal was detected at the N-terminal region of the ANV-ORF2-MK4 strain.

Conclusion:
This study represents the first genetic characterization of ANV strains circulating in Vietnam based on the ORF2 gene. The findings provide additional insights into the genetic diversity of the ANV ORF2 gene.

Key words: Avian nephritis virus, Ben Tre province, genetic characterization, ORF2, Vietnam