Development of neutralizing antibody responses in muskellunge, Esox masquinongy (Mitchill), experimentally exposed to viral haemorrhagic septicaemia virus (genotype IVb).

A complement-dependent 50% plaque neutralization test was used to assess the neutralizing antibody response in sera of muskellunge, Esox masquinongy, experimentally infected with viral haemorrhagic septicaemia virus (VHSV, genotype IVb) by immersion. Groups of muskellunge were challenged with varying concentrations of VHSV: Group 1 with 10(2) plaque-forming units (pfu) mL(-1) , Group 2 with 4 × 10(3)  pfu mL(-1) , Group 3 with 10(5)  pfu mL(-1) and Group 4 with 0 pfu mL(-1) . The fish were held at a temperature of 11 ± 1 °C and were sampled over a 20-week period. Neutralizing antibodies were not detected in sera of any of the negative control fish throughout the study. Low neutralizing titres were detected in Groups 1-3 by 6 days post-infection (p.i.). Neutralizing titres of ≥80 [corrected]. were not detected again until 3, 4 and 7 weeks p.i. for Groups 2, 3 and 1, respectively, with peak titres for those groups occurring 16, 11 and 17 weeks p.i., respectively. VHSV was detected in serum for up to 11 weeks p.i. Results of this study show that survivors can be detected by a serological technique, despite being virus negative. This may benefit the investigation of VHSV IVb distribution in the Great Lakes and the study of host immune responses to this emerging sublineage.