Identification of equine herpesviruses (EHV) in horses presented for evaluation of respiratory disease and/or poor performance

Introduction: The aim of this study was to evaluate the contribution of equine herpesviruses (EHV) to respiratory disease and poor performance, and to identify factors associated with infection.
Materials and methods: Respiratory tract (nasal swab, tracheal wash, bronchoalveolar lavage fluid) and peripheral blood samples were evaluated from 98 horses with owner-identified respiratory disease and/or poor performance. Results were compared with samples from 127 healthy adult horses. Within the population presented for veterinary examination, relationships between physical examination, clinical pathology and virology results were examined by multivariate logistic regression.
Results: Respiratory samples from 47/94 horses (50%) presented for respiratory disease and/or poor performance were positive for EHV. Identification of EHV1 and EHV4 infection was based on tracheal wash and/or bronchoalveolar lavage samples from 12 horses when nasal swabs were negative. Concurrent infection with multiple EHV was evident in both populations. Within the group presented for veterinary examination, horses from which EHV were identified in respiratory samples were more likely to have a history of acute disease, pyrexia, systemic illness and poor performance. Haematology and airway cytology did not discriminate virus positive horses.
Conclusion: EHV were identified more commonly in nasal swabs from horses presented for respiratory disease and/or poor performance than control horses. Evaluation of the contribution of EHV to respiratory disease of horses requires samples from the lower respiratory tract, techniques permitting recognition of co-infection with multiple EHV and discrimination of latent EHV infection.