Development of an antigen-capture ELISA for the detection of equine influenza virus nucleoprotein

An antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) was developed for the detection of the equine influenza virus (EIV), employing monoclonal and polyclonal antibodies against the A/equine/Xingjiang/2007 (H3N8) nucleoprotein (NP). Immunoglobulin G antibodies were purified and used as capture or detector antibodies. The specificity of the optimized AC-ELISA was evaluated using EIV, equine herpesvirus 1 (EHV-1), equine herpesvirus 4 (EHV-4), equine arteritis virus (EAV) and Japanese encephalitis virus (JEV), resulting in only EIV specimens yielding a strong signal. A minimal concentration of 50 ng/ml EIV protein was detected in Nonidet P40-treated virus preparations. Virus from the nasal swabs of equines infected experimentally were detected from days 3 to 7 post-infection using this AC-ELISA, with results confirmed by virus isolation and multi reverse transcription polymerase chain reaction. Both H3N8 and H7N7 EIV subtypes were AC-ELISA positive, indicating that this assay is suitable for the detection of all EIV subtypes.