Serum and mucosal antibody testing to detect viral exposure in contact horses during an equine herpesvirus myeloencephalopathy outbreak.

Abstract

OBJECTIVE: To apply equine herpesvirus type 1 (EHV-1) antibody testing in nasal swabs and serum in nonclinical horses during a naturally occurring outbreak of (EHV-1). Previous experimental EHV-1 challenge studies showed stable serum anti-EHV-1 antibody concentrations paired with rapidly increasing nasal mucosal antibodies (mucAbs) prevent EHV-1 infection, viral shedding, and cell-associated viremia. From this, we hypothesized that EHV-1 antibody testing can confirm exposure in non-clinical horses during an outbreak. METHODS: 2 horses with neurological signs from 1 farm were admitted to an equine hospital. Equine herpesvirus type 1 was confirmed by PCR. Five concurrently hospitalized, possibly exposed horses, 4 of which were vaccinated against EHV-1 and -4 within 7 months, were studied. Possibly exposed horses had their temperatures measured along with serum and nasal swab samples taken for EHV-1 PCR and antibody quantification between 1 and 29 days of potential EHV-1 exposure. RESULTS: None of the possibly exposed horses developed fever or clinical signs of EHV-1. Polymerase chain reaction results on nasal swabs and blood were negative. Only mild seroconversion was observed. Mucosal antibodies were initially low and increased rapidly in 4 possibly exposed horses that were considered exposed to EHV-1 yet neither infected (protected) nor infectious. One nonimmune horse without increasing mucAbs was not exposed. CONCLUSIONS: MucAbs provide information on EHV-1 exposure and, together with clinical monitoring and PCR, enable improved management of equine herpesvirus myeloencephalopathy outbreaks. Serum antibodies obtained at the same time provide information on preexisting EHV-1 immunity. CLINICAL RELEVANCE: Repeatedly measuring the serum and mucAbs of possibly exposed horses during an EHV-1 outbreak, starting shortly after the index case is confirmed, may identify nonimmune horses and possibly exposed animals that are protected to make informed treatment decisions (nonimmune) and reduce quarantine time (protected horses).