• EHV-1;
  • Reactivation;
  • Transmission

Background: Recrudescence of latent equine herpesvirus 1 (EHV-1) with subsequent viral shedding via nasal secretions is a potential source of infection for susceptible horses and has been implicated in outbreaks occurring in closed populations.

Objectives: To describe the viral kinetics of reactivated EHV-1 in blood and nasal secretions from latently infected horses after administration of corticosteroids, and to study the infectious nature of reactivated EHV-1 to sentinel horses.

Animals: Eight healthy horses.

Methods: Four horses infected 4 months previously with EHV-1 received dexamethasone on 5 consecutive days. Four seronegative horses served as sentinels and had direct contact with the latently infected horses. All horses were monitored daily for development of clinical signs. Whole blood and nasal secretions were collected daily for molecular detection and cell culture of EHV-1. Serum was collected weekly for the detection of antibodies against EHV-1.

Results: All horses in the latently infected group showed transient molecular detection of EHV-1 in blood and nasal secretions, but only 1 horse developed fever. Three latently infected horses developed an increase in antibody concentrations against EHV-l. Viral cultures remained negative for all latently infected horses after corticosteroid administration. None of the sentinel horses developed clinical signs, viremia, viral shedding, or seroconversion.

Conclusions and Clinical Importance: EHV-1 was successfully reactivated after corticosteroid administration in latently infected horses. However, transmission of reactivated virus to sentinel horses was unsuccessful. Failure to effectively transmit EHV-1 to susceptible horses may have resulted from the low level and short period of viral shedding in latently infected horses.