Background: Equine influenza virus (EIV) is one of the most important pathogens causing respiratory signs in equids. Rapid antigen detection (RAD) kits are useful for point-of-care testing because they are user-friendly and provide fast results. Although sensitive and broad-reactive RAD kits are needed for controlling horse movement, no RAD kits specified for EIV are available.

Objective: This study evaluated the usefulness of seven RAD kits originally developed for human influenza and available in Japan during 2023-2024 for EIV antigen detection.

Study design: Experimental assay comparison.

Methods: The detection limits of each RAD kit were determined using five-fold serial dilutions of two H3N8 EIV strains. According to the results of the detection limits, the three most sensitive RAD kits (Quick Chaser Auto Flu A, B, Finevision Influenza, and RapidTesta Flu·NEXT) were further evaluated using nasopharyngeal swabs of horses experimentally infected with EIV.

Results: With reverse-transcription quantitative polymerase chain reaction (RT-qPCR) as a reference assay, the sensitivities of Quick Chaser Auto Flu A, B, RapidTesta Flu·NEXT, and Finevision Influenza were 63%, 61%, and 54%, respectively.

Main limitation: Samples from naturally infected horses were not tested.

Conclusions: Since the sensitivities for detecting EIV antigens vary, choosing the appropriate RAD kits is essential. Although RAD kits are less sensitive than RT-qPCR, RAD kits are useful for detecting EIV antigens as ancillary diagnostic tools in the field.