Salmonid fish viruses and cell interactions at early steps of the infective cycle

Abstract

A flow cytometric virus-binding assay that directly visualizes the binding and entry of infectious pancreatic necrosis virus (IPNV), infectious haematopoietic necrosis virus (IHNV) and virus haemorrhagic septicaemia virus (VHSV) to several cell lines was established. The highest efficiency of binding was shown by the BF-2 cell line and this was used to study, at the attachment level, the interactions of these cells with salmonid fish viruses in coinfections, and to further determine if the earliest stage of the viral growth cycle could explain the previously described loss of infectivity of IHNV when IPNV is present. Our results demonstrated that IPNV binds to around 88% of cells either in single or dual infections, whereas IHNV attachment always decreased in the presence of any of the other viruses. VHSV binding was not affected by IPNV, but coinfection with IHNV reduced the percentage of virus-binding cells, which suggests competition for viral receptors or co-receptors. Internalization of the adsorbed IHNV was not decreased by coinfection with IPNV, so the hypothetical competence could be restricted to the binding step. Treatment of the cells with antiviral agents, such as amantadine or chloroquine, did not affect the binding of IPNV and VHSV, but reduced IHNV binding by more than 30%. Tributylamine affected viral binding of the three viruses to different degrees and inhibited IPNV or IHNV entry in a large percentage of cells treated for 30 min. Tributylamine also inhibited IHNV cytopathic effects in a dose-dependent manner, decreasing the virus yield by 4 log of the 50% endpoint titre, at 10 mm concentration. IPNV was also inhibited, but at a lower level. The results of this study support the hypothesis that IHNV, in contrast to VHSV or IPNV, is less efficient at completing its growth cycle in cells with a simultaneous infection with IPNV. It can be affected at several stages of viral infection and is more sensitive to the action of antiviral compounds.

Limited Interference at the Early Stage of Infection between Two Recombinant Novirhabdoviruses: Viral Hemorrhagic Septicemia Virus and Infectious Hematopoietic Necrosis Virus

“…Nevertheless, a more restricted distribution of IHNV in internal organs could be observed during the acute stage of the disease, and no virus was detected in the brain. The small reduction of the percentage of infection of both viruses between single and dual infections (96 versus 89% in average, respectively, for VHSV and 97 versus 73% in average, respectively, for IHNV) are comparable to the reduction of VHSV and IHNV binding on the cell surface as estimated with biotinylated viruses in single and double infections (91 versus 72% for VHSV and 91 versus 76% for IHNV, respectively) (17). These results suggest that the light interference observed between the two viruses could be explained by a competition for the same cell receptor as that demonstrated by Bearzotti et al, who identified the fibronectin as a major cell component allowing fish rhabdoviruses to bind to the target cells (3).…”

Effect of the coexistence on the replication of striped jack nervous necrosis virus (SJNNV) and red-spotted grouper nervous necrosis virus (RGNNV) using an in vitro approach

“…In fact, several VNNV reassortant isolates have been obtained from cultured diseased Senegalese sole and gilt‐head seabream (Toffolo et al., ; Olveira et al., ). The coexistence of two different viruses in a single animal may affect the course of both viral infections, as has been previously described for several fish viruses (Chinchar et al., ; Johansen and Sommer, ; Pakingking et al., ; Byrne et al., ; de las Heras et al., ; Kuo et al., ). Regarding the nodavirus, Nishizawa et al.…”

“…(). This inhibition may be the consequence of the replication of the first virus, the competence for the same cellular receptors (de las Heras et al., ), the induction of an antiviral factor (Chinchar et al., ), or it may be caused by the stimulation of the host interferon (IFN)‐mediated immune system by the first‐inoculated virus (Johansen and Sommer, ; Byrne et al., ). However, the implication of the host IFN‐mediated immune system on the superinfective virus replication could not be tested in this work due to the lack of knowledge regarding the E‐11 immunogenic sequences.…”

Trout and Salmon Viruses

“…The actual cause of the reduced pathogenesis is not known, but IPNV interferes with IHNV replication in cell cultures as well (Alonso et al 1999). Using green fluorescent protein labeled IHNV, VHSV and IPNV in flow cytometry experiments on BF-2 cells, de las Heras et al (2008) demonstrated a significant inhibition of IHNV uptake when coinfected with IPNV but no inhibition of VHSV uptake in IPNV coinfections. Using green fluorescent protein labeled IHNV, VHSV and IPNV in flow cytometry experiments on BF-2 cells, de las Heras et al (2008) demonstrated a significant inhibition of IHNV uptake when coinfected with IPNV but no inhibition of VHSV uptake in IPNV coinfections.…”

“…A study examining competition for receptors as possible cause of this inhibition was conducted by de las Heras et al (2008). Furthermore, in a coinfection one virus can suppress the replication of other viruses.…”