Detection and phylogenetic analysis of infectious pancreatic necrosis virus in Chile

Infectious pancreatic necrosis virus (IPNV) is the etiological agent of a highly contagious disease that is endemic to salmon farming in Chile and causes great economic losses to the industry. Here we compared different diagnostic methods to detect IPNV in field samples, including 3 real-time reverse transcription PCR (qRT-PCR) assays, cell culture isolation, and indirect fluorescent antibody test (IFAT). Additionally, we performed a phylogenetic analysis to investigate the genogroups prevailing in Chile, as well as their geographic distribution and virulence. The 3 qRT-PCR assays used primers that targeted regions of the VP2 and VP1 genes of the virus and were tested in 46 samples, presenting a fair agreement within their results. All samples were positive for at least 2 of the qRT-PCR assays, 29 were positive for cell culture, and 23 for IFAT, showing less sensitivity for these latter 2 methods. For the phylogenetic analysis, portions of 1180 and 523 bp of the VP2 region of segment A were amplified by RT-PCR, sequenced and compared with sequences from reference strains and from isolates reported by previous studies carried out in Chile. Most of the sequenced isolates belonged to genogroup 5 (European origin), and 5 were classified within genogroup 1 (American origin). Chilean isolates formed clusters within each of the genogroups found, evidencing a clear differentiation from the reference strains. To our knowledge, this is the most extensive study completed for IPNV in Chile, covering isolates from sea- and freshwater salmon farms and showing a high prevalence of this virus in the country.