Effect of raising water temperature on proliferation of hirame novirhabdovirus (HIRRV) and antiviral response of olive flounder (Paralichthys olivaceus)

Abstract

Hirame novirhabdovirus (HIRRV) is a serious viral pathogen of olive flounder and causes high mortality and significant economic losses. However, the virulence of HIRRV to olive flounder could be greatly affected by the water temperature, which would be significantly attenuated when the water temperature was increased from 10 to 20 °C. In this study, Olive flounders were artificially infected with the HIRRV CNPo2015 strain at 10 °C, and then a water temperature shift-up (T-Sup) to 20 °C were carried out at 0, 12, 24 or 72 h post infection (hpi). Results showed that the mortality rates of 0 and 6.67% were observed in the groups with a T-Sup at 0 and 12 hpi, respectively, which were lower than that of the group (96.67%) with a T-Sup at 72 hpi. Also, significantly lower virus copy numbers were detected in the olive flounder with a T-Sup at 0, 12, 24 hpi compared to the olive flounders with a T-Sup at 72 hpi. The percentage of CD8+ T lymphocytes in spleen was obviously increased post viral infection, whereas which was significantly higher in the olive flounders with a T-Sup at 0 and 12 hpi than the olive flounders with a T-Sup at 72 hpi. Meanwhile, the expressions profiles of 6 antiviral-related genes, including two IFNs genes (typeI IFN and Mx), two proinflammatory genes (TNFα and IL-1β) and two antigen presenting-related genes (CD8α, MHCIα) revealed that earlier T-Sup could induce significantly quicker and stronger up-regulation of antiviral-related genes. Taking together, these results demonstrated that shifting cultivating water temperature from 10 to 20 °C at early stage after HIRRV infection could evoke a quick and strong antiviral immune response in olive flounders and paly an effectively protective role against HIRRV infection, which indicated that water temperature shift-up was a promising measure for the prevention of HIRRV infection. While commercially available vaccines are not yet available for olive flounder, our results showed the possibility of developing effectively preventive measures against HIRRV by manipulation of water temperature.