Infectious hematopoietic necrosis virus enhanced infectious pancreatic necrosis virus multiplication during co-infection in Chinook salmon embryo cell lines

Abstract

Complicated viral interactions make viral co-infections more difficult to treat. Co-infection of infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) causes huge economic losses to the salmonid industry in China. To reveal the impact of IHNV on IPNV during co-infection, Chinook salmon embryo (CHSE-214) cells were inoculated with IHNV prior to or after IPNV at different time intervals, and propagation of IPNV was determined at the RNA, protein, and virion levels by real-time quantitative polymerase chain reaction (RT-qPCR), an immunofluorescence antibody test (IFAT), flow cytometry, and virus titration. Taken together, the results showed that IPNV multiplication was enhanced in all of the co-infection groups compared with the single IPNV infection group. This enhancement became stronger with an increasing infection time interval irrespective of the infection order, and the highest IPNV multiplication level was observed when IHNV was inoculated 12 h after IPNV (P12H). Compared with the single IPNV infection group, the IPNV RNA level in the P12H group was at least 10-fold higher, the proportions of IPNV-infected cells determined by IFAT and flow cytometry were approximately 2-fold higher, and the viral titer was about 40-fold higher. A significant difference was detected between each group in which IHNV was inoculated after IPNV. These findings suggested that a synergistic effect was induced by IHNV over IPNV, and IPNV multiplication was enhanced during co-infection in CHSE-214 cells. This enhancement was dependent on the infection time interval but not the infection order and the synergistic effect became stronger with increasing infection time interval within the study period.