Comparison among three different serological methods for the detection of equine influenza virus infection

The equine influenza virus (EIV) H3N8 subtype is responsible for all EIV outbreaks worldwide while the H7N7 subtype is less pathogenic and is considered extinct as it has not been confirmed in outbreaks since 1980. Although EIV is enzootic in Brazil, few reports describe the actual EIV antibody status in the country. The aims of this study were: - to evaluate the efficiency of different serum treatments described by the World Organisation for Animal Health (OIE) and the World Health Organization (WHO) to remove non-specific haemagglutination inhibitors for the haemagglutination inhibition (HI) assay for EIV - to evaluate the presence of EIV antibodies by HI, enzyme-linked immunosorbent assay and agar gel immunodiffusion in 83 non-vaccinated equines from São Paulo State - to evaluate a strategy to better analyse equine sera for EIV antibodies. Although there was no statistical difference among treatments, receptor-destroying enzyme treatment followed by chicken erythrocyte adsorption showed more consistent results, which corroborate the OIE and WHO recommendation to use this treatment preferentially. The HI results suggest equine H3N8 virus circulation among the animals tested from São Paulo State. The algorithm suggested here could be used to guide antibody detection against equine influenza virus in equines, improving the test specificity by aiming to avoid false positive results.