Detection and genotyping of an infectious pancreatic necrosis virus from asymptomatic rainbow trout (Oncorhynchus mykiss) facilities in Mexico

Background: Infectious pancreatic necrosis virus (IPNV) is a birnavirus that causes a lethal disease in both hatchery-reared juvenile salmonids and other non-salmonid fishes. IPNV has been classified into seven genogroups based on the analysis of the VP2/NS junction region of the viral A RNA segment. Methods: Ten organisms from two trout-rearing farms were used for viral isolation in RTG-2 cells. Cells were inoculated with samples from spleen, kidneys and pyloric caeca. The viral isolate was initially identified by electron microscopy, and confirmed by a commercial ELISA, RT-PCR and sequencing. A phylogenetic tree was constructed based on the deduced amino acids sequence of VP2. Results: An IPNV genogroup 1, labeled as EdoMex07, was isolated from a pool of renal tissues of five asymptomatic trout. The amino acid sequence analysis of VP2 showed that this IPNV presented the putative VP2 residue (221) already described in asymptomatic trout carriers. Conclusions: The EdoMex07 IPNV isolate belongs to genogroup 1, and has a VP2 phenotype which has been suggested to be involved in the establishment of the carrier state. This EdoMex07 IPNV is currently used as the standard positive control for detection of IPNV in rainbow trout farms in Mexico.