Aquabirnaviruses, such as the infectious pancreatic necrosis virus (IPNV), Novirhabdoviruses, such as the infectious hematopoiteic necrosis virus (IHNV) and the viral hemorrhagic septicemia virus (VHSV), cause considerable losses to the salmonid industry worldwide. Coinfections of 2 viruses have been described, but the interactions between rhabdoviruses and birnaviruses have not been examined closely. Using virus titration, flow cytometry and RT-PCR assays, we compared the effect of IPNV on the replication of IHNV and VHSV in tissue culture cells. RT-PCR assays indicated that simultaneous infection of IPNV with VHSV does not affect the replication of the rhabdovirus either in the first or successive passages; the infective titers were similar in single and double infections. In contrast, coinfection of IPNV with IHNV induced a fall in infectivity, with reduced expression of IHNV viral antigens in BF-2 cells from Lepomis macrochirus and a loss of 4.5 log 10 units of the infective titer after 3 successive passages. It was possible to stimulate BF-2 cells to produce significant interferon-like activity against IHNV but not against VHSV.
KEY WORDS: Infectious pancreatic necrosis virus · Infectious hematopoiteic necrosis virus · Viral hemorrhagic septicemia virus · Coinfections · Fish viruses
Resale or republication not permitted without written consent of the publisherDis Aquat Org 67: [183][184][185][186][187][188][189][190] 2005 provides some protection against the secondary ISAV infection (Johansen & Sommer 2001). Melby & Falk (1995) infected an IPNV carrier stock of Atlantic salmon with tissue homogenates containing the infectious salmon anemia virus (ISA), and demonstrated that ISA infection did not activate the latent IPNV infections. More recently, Pakingking et al. (2003) explored experimental dual infections in flounder Paralichthys olivaceus with an aquabirnavirus and the VHSV on the one hand, and bacteria on the other. They concluded that the primary infection suppresses the secondary viral infection, but facilitates the bacterial infection. Further, the studies by Brudesth et al. (2002) on interactions between VHSV and IHNV during an experimental coinfection of rainbow trout demonstrated a reduced systemic distribution of IHNV.All these reports indicate that interactions between viruses during simultaneous infections is as interesting a line of research in fishes, as it is proving to be in mammals. In previous studies we reported that IPNV interferes with the replication of IHNV in tissue culture cells and in fishes (Alonso et al. 1999a(Alonso et al. , 2003. The aim of the present study was to determine whether coinfections of VHSV or IHNV with IPNV present similar features; i.e. whether VHSV growth is affected in a similar way to that of IHNV and whether its infectivity is reduced. This is relevant to diagnoses, since the detection methods for viral coinfections would need to be improved, as rapid identification could prevent further spread. In addition, little is known about interacti...