Evaluation of ELISA and haemagglutination inhibition as screening tests in serosurveillance for H5/H7 avian influenza in commercial chicken flocks

Abstract

Avian influenza virus (AIV) subtypes H5 and H7 can infect poultry causing low pathogenicity (LP) AI, but these LPAIVs may mutate to highly pathogenic AIV in chickens or turkeys causing high mortality, hence H5/H7 subtypes demand statutory intervention. Serological surveillance in the European Union provides evidence of H5/H7 AIV exposure in apparently healthy poultry. To identify the most sensitive screening method as the first step in an algorithm to provide evidence of H5/H7 AIV infection, the standard approach of H5/H7 antibody testing by haemagglutination inhibition (HI) was compared with an ELISA, which detects antibodies to all subtypes. Sera (n = 1055) from 74 commercial chicken flocks were tested by both methods. A Bayesian approach served to estimate diagnostic test sensitivities and specificities, without assuming any 'gold standard'. Sensitivity and specificity of the ELISA was 97% and 99.8%, and for H5/H7 HI 43% and 99.8%, respectively, although H5/H7 HI sensitivity varied considerably between infected flocks. ELISA therefore provides superior sensitivity for the screening of chicken flocks as part of an algorithm, which subsequently utilises H5/H7 HI to identify infection by these two subtypes. With the calculated sensitivity and specificity, testing nine sera per flock is sufficient to detect a flock seroprevalence of 30% with 95% probability.

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) from the 2021/22 epizootic is highly duck adapted and poorly adapted to chickens

“…The duck sera were pre-absorbed by adding packed chicken red blood cells and incubated in at 4 °C overnight to prevent non-specific agglutination. The beta-propiolactone inactivated viral antigen [34] A/Chicken/Wales/053969/21 (H5N1) (GISAID Accession number EPI_ISL_9012618), representative of the antigenic profile of the 2021/22 H5N1 epizootic, was used at four HA units. Reciprocal HAI titres of greater than 1/16 were considered seropositive [23].…”

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) from the 2021/22 epizootic is highly duck adapted and poorly adapted to chickens

“…The duck sera were pre-absorbed by adding packed chicken red blood cells and incubated in at 4 °C overnight to prevent non-specific agglutination [28]. The beta-propiolactone inactivated viral antigen [34] A/Chicken/Wales/053969/21 (H5N1) (GISAID Accession number EPI_ISL_9012618), representative of the antigenic profile of the 2021/22 H5N1 epizootic, was used at four HA units. Reciprocal HAI titres of greater than 1/16 were considered seropositive [28].…”

Surveillance of avian influenza and Newcastle disease viruses in backyard poultry raised near migratory bird sites in Mato Grosso state, Brazil

“…2). As the ELISA has high sensitivity and the sample size was large, the possibility of false positive results should be considered, especially in the face of inconclusive results in the HI assays (26). Highly pathogenic AI is rare in Brazil; thus, vaccination is prohibited throughout the country (27).…”