Antibody Testing to Detect Viral Exposure in Contact Horses During an Equine Herpes Myeloencephalopathy Outbreak

Abstract: Background -Two experimental EHV-1 challenge studies showed moderate serum antibody concentrations paired with a rapid increase in nasal mucosal anti-EHV antibodies (mucAbs) prevent infection and viral shedding. Measuring mucAbs in an EHV-1 outbreak may allow for reduced quarantine time for in-contact animals that are protected.Hypothesis/Objectives –Our objective was to apply this test to a naturally occurring EHV-1 incident. We hypothesized that combined PCR and EHV-1 antibody testing could identify exposure in non-clinical horses during an outbreak.Animals – Two horses with neurological signs from one farm admitted to an equine hospital. EHV-1 was confirmed by PCR on a nasal swab in one horse. Five concurrently hospitalized horses that were previously vaccinated against EHV-1/4. Methods – Descriptive longitudinal study. In-contact horses were monitored for clinical signs. Serum and nasal swab samples were taken for EHV-1 PCR and antibody quantification (EHV-1 Risk Evaluation Assay, Cornell University) between days 6 to 21 of potential EHV-1 exposure. Results – None of the in-contact horses developed fever or clinical signs. All PCR results were negative. Only mild seroconversion was observed. MucAbs were initially low and increased rapidly in four in-contact horses who were considered exposed to EHV-1 yet neither infected nor infectious. One horse without an increase in mucAbs was not exposed.Conclusions/clinical importance – MucAb testing and PCR should be performed in potentially exposed horses as soon as the EHM index case is confirmed. MucAbs provide information on EHV-1 exposure and, together with clinical monitoring and PCR, enable improved management of EHM outbreaks.