DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03185

Viral haemorrhagic septicaemia virus remains viable for several days but at low levels in the water flea Moina macrocopa

Takafumi Ito*, Niels Jørgen Olesen

*Email: takafumi@fra.affrc.go.jp

ABSTRACT: Viral haemorrhagic septicaemia virus (VHSV) genotype IVb has been isolated from amphipods belonging to the genus Diporeia, but it has yet to be established whether crustacean zooplankton act as vectors of this virus for fish species. Therefore, this study evaluated the viability of infectious VHSV in the water flea Moina macrocopa. VHSV was re-isolated from replicate groups of M. macrocopa that had been immersed with 108.0, 107.0 and 105.0 TCID50 ml1 of VHSV (DK-3592B, genotype Ia). Furthermore, 40 M. macrocopa that had been immersed with 108.0 TCID50 ml1 of VHSV for 72 h had VHSV titers of 102.7–104.3 TCID50. Thus, VHSV was clearly taken up by M. macrocopa and remained viable in this crustacean for several days. However, no mortality was observed over a 28-day period in rainbow trout Oncorhynchus mykiss that were fed VHSV-contaminated M. macrocopa for 14 days and it was found that the virus titer significantly decreased after a 4h incubation with pyloric caeca extracts from rainbow trout, indicating that passage through the gut is likely to result in a significant decrease in viral titer. This may explain why consumption of prey containing low levels of VHSV did not result in causing clinical VHS.