Seroprevalence of Infectious Respiratory Agents in Thoroughbred Race Horses at the Seoul Race Park, Republic of Korea

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Infectious respiratory disease is one of the most frequent causes of lost days in training and reduced performance of Thoroughbred racehorses. Equine influenza virus (EIV), Equine herpesvirus-1 (EHV-1) and -4 (EHV-4), equine rhinitis virus A (ERAV) and B (ERBV), and Streptococcus equi subspecies equi (S. equi) are important infectious agents of the respiratory tract of horses. The purpose of this study was to determine the seroprevalence of EHV-1, EHV-4, ERAV, ERBV, and S. equi and to measure EIV antibody levels of Thoroughbred racehorses at Seoul Race Park (SRP), Republic of Korea. All horses had previously been vaccinated against EIV and S. equi, but not against any of the other pathogens that were tested. A total of 94 serum samples, which were collected from race participants at the SRP were tested using the single radial haemolysis (SRH) test for EIV (H3N8), the complement-fixation (CF) test for EHV-1, EHV-4, ERAV, ERBV and an indirect enzyme-linked immunosorbent assay (iELISA) for S. equi. Serum samples from seventy eight out of 94 horses (83%) generated zones of over 85 mm2 in the SRH test, which classified them as clinically protected against EIV (H3N8). The most sero-prevalent agent detected was EHV-4 (30.9%, 29/94), followed by EHV-1 (9.6%, 9/94), S. equi (2.1%, 2/94), ERAV (1.1%, 1/94) and ERBV (1.1%, 1/94). All horses showed no visual clinical signs. The present study showed that the seroprevalence of infectious respiratory agents was relatively low and provides evidence of low risk of respiratory infectious agents in Thoroughbred race horses at SRP.