Molecular surveillance and genetic characterization of infectious pancreatic necrosis virus in rainbow trout farms of East Azerbaijan, Iran.

Infectious pancreatic necrosis virus (IPNV), a member of the Birnaviridae family, is a significant pathogen in salmonid aquaculture, causing notable economic losses worldwide. This study aimed to detect and genetically characterize IPNV in rainbow trout (Oncorhynchus mykiss) farms in East Azerbaijan Province, Iran. Sampling was conducted at 12 farms. Five tissue samples were taken from each farm. A total of 60 tissue samples from juvenile fish (<10 g) were collected across 12 farms. RNA was extracted and subjected to nested reverse transcription polymerase chain reaction (RT-PCR) targeting the NS/VP3 region in segment A of the IPNV genome. The virus was detected in 8 out of 60 samples (13.3 %), with positive cases identified in three farms. Sequencing was performed on four positive samples. Sequence analysis of four representative isolates (PP316090, PP316091, PP429499, PP429500) revealed high nucleotide similarity to previously reported Iranian strains from Shiraz and Ahvaz, as well as European strains, particularly from Spain and Turkey. Phylogenetic analysis confirmed close clustering with endemic Iranian isolates, indicating minimal genetic variation and possible intra-regional transmission. The persistence of genetically stable strains over time suggests that current biosecurity measures may be insufficient to prevent viral spread. These results highlight the need for improved monitoring systems, targeted molecular diagnostics, and the development of region-specific vaccines to manage IPNV effectively. Furthermore, the genetic resemblance to European isolates highlights the importance of broader epidemiological studies. Continued molecular surveillance and strain tracking are essential for early detection and control. Future studies should also explore the pathogenic potential of local strains and assess their impact on fish health and farm productivity under field conditions.