Infectious hematopoietic necrosis virus promoted infectious pancreatic necrosis virus multiplication during co-infection in rainbow trout (Oncorhynchus mykiss)

Because plenty of pathogenic microbe exist in natural aquatic environments, co-infection is common. Infectious hematopoietic necrosis (IHN) and infectious pancreatic necrosis (IPN) are prevalent viral diseases in cultured salmonids, with infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) known to infect rainbow trout ( Oncorhynchus mykiss ). To understand the influence of IHNV on IPNV in co-infection in rainbow trout, we intraperitoneally (ip) inject rainbow trout with IHNV at different time intervals prior to or after IPNV injection, and determine propagation of IPNV with absolute quantitative analysis in brain, gill, heart, liver, spleen and head kidney tissues. Meanwhile, to prove the existence and replication of IHNV in co-infections, IHNV loads were also detected by real-time quantitative polymerase chain reaction (RT-qPCR). For rainbow trout ip-injected with IHNV simultaneously or after IPNV, IPNV multiplication increases ( P < 0.05) in each tissue. For rainbow trout ip-injected with IHNV 2 d prior to IPNV (H2P), levels of IPNV are enhanced ( P < 0.05) in all but brain and heart tissues on 2 d post IPNV infection. For rainbow trout ip-injected with IHNV 7 d prior to IPNV (H7P), IPNV multiplication increases ( P < 0.05) only in gill, heart, liver, spleen and head kidney tissues on 7 d post IPNV infection. At the same time, antiviral responses also occurred in all challenge groups. Results reveal that ip injection of IHNV simultaneously or after IPNV can enhance IPNV multiplication in in vivo co-infection, and that when ip injection of IHNV occurs prior to IPNV injection, IPNV multiplication can also be enhanced, although premature injection of IHNV does not obviously affect IPNV proliferation. • IHNV promotes replication of IPNV in co-infection. • The effect of IHNV in six different tissues on IPNV replication was examined. • Rainbow trout were intraperitoneally injected with IHNV at different time intervals prior to or after IPNV injection.