Detection of rainbow trout antibody to Egtved virus by enzyme-linked immunosorbent assay (ELISA), immunofluorescence (IF), and plaque neutralization tests (50%PNT)

Abstract

The humoral immune response to Egtved virus, the causative agent of viral haemorrhagic septicaemia (VHS) in rainbow trout Oncorhynchus mykiss, was investigated by means of the enzyme-linked immunosorbent assay (ELISA), immunofluorescence (IF), and the 50% plaque neutralization test (50% PNT). Sera from fish immunized with virus under aquarium conditions as well as sera collected from fish in farms with different VHS status were included in the experiments. ELISA proved to be more sensitive and less time- and material-consuming than either IF or 50% PNT. Using Elisa, antibody to Egtved virus was found in 54% of fish from infected trout farms examined while only 16% were positive by 50% PNT. The IF test had a sensitivity close to that of ELISA, but was less suitable for examination of large numbers of sera. Non-neutralizing antibodies tend to persist longer after VHS infection than neutralizing antibodies. The kinetics of the antibody response was close to that previously published. No anamnestic immune response was observed with any of the tests. We conclude that our ELISA is well suited for VHS surveillance.