Evaluation of the kinetics of anti‐NP and anti‐HA antibody after infection of Pekin ducks with low pathogenic avian influenza virus

Serological monitoring is a feature of surveillance programmes for the detection of the circulation of notifiable low pathogenic avian influenza (LPAI) viruses in commercial poultry holdings. Commercial multispecies nucleoprotein (NP) enzyme-linked immunosorbent assays (ELISAs) have been replacing the haemagglutination inhibition (HI) test as pre-screening tools. Few comparative studies have been conducted to test sera from domestic ducks for diagnostic purposes. Therefore, we evaluated the correlation between commercial NP ELISAs and the HI test. Anti-NP and anti-haemagglutinin (HA) antibodies were measured in sera from domestic ducks that had undergone serological screening and from juvenile domestic Pekin ducks that were experimentally infected with LPAI viruses. The findings highlight an absence of a correlation between NP ELISA and HI results with both field and experimental duck sera. Dissimilar kinetics of the antibodies detected during the follow-up evaluation of the humoral immune responses in experimentally infected ducks may explain this lack of correlation. Indeed, anti-NP titres decreased over time, whereas anti-HA titres remained unchanged after inoculation with the H3N1 LPAI virus isolated from domestic duck or the H7N1 LPAI virus isolated from chicken. Despite these differences, the NP ELISA may serve as a valid pre-screening tool to detect circulating LPAI viruses in domestic duck populations at the flock level.