Investigation of the Systemic Antibody Response and Antigen Detection Following Intranasal Administration of Two Commercial Equine Herpesvirus-1 Vaccines to Adult Horses.

EHV-1 vaccines are often administered intranasally during emergency situation such as outbreaks of equine herpesvirus myeloencephalopathy. However, there is currently no data available on the efficacy of such protocols, nor the diagnostic challenge when recently vaccinated horses become clinically infected and nasal secretions are collected to support a diagnosis of EHV-1 infection. Therefore, the objective of this study was to determine if two commercially available EHV-1 vaccines, a killed-adjuvanted (Calvenza) and a modified-live (Rhinomune) EHV-1 vaccine, could induce a measurable systemic antibody response postintranasal administration. A second objective was to determine the detection time of EHV-1 in nasal secretions by qPCR following the intranasal administration of the respective EHV-1 vaccines. Thirty healthy adult horses, with no recent EHV-1 vaccine administration, were randomly assigned to one of three groups: Rhinomune group, Calvenza group, and unvaccinated control group. Total Ig and isotype-specific IgG4/7 against EHV-1 measured pre- and 30-days post-vaccination were not different amongst the three study groups. Vaccine-derived EHV-1 was only detected in the two EHV-1 vaccine groups with 9/10 horses in the Rhinomune group and 8/10 horses in the Calvenza group testing qPCR-positive for EHV-1 for 1 to 3 days. There was no significant difference in number of horses testing qPCR-positive for EHV-1 and absolute quantitation of EHV-1 in nasal secretions by qPCR between the two vaccine groups. The intranasal administration of two commercial EHV-1 vaccines did not elicit a systemic immune response. Further, vaccine derived EHV-1 could be detected in the majority of the intranasally vaccinated horses, potentially impacting diagnostic interpretation of EHV-1 during outbreak situations.