Equine Herpesviruses (EHV) are highly prevalent and often latent pathogens of equids which can be fatal when transmitted to non-equids. Stress and elevated glucocorticoids have been associated with EHV reactivation in domestic horses, but little is known about the correlation of stress and viral reactivation in wild equids. We investigated the effect of environmental stressors (long-distance transport and social group restructuring) on EHV reactivation in captive Grévys zebras. One mare was translocated by road transport from Zoo Mulhouse, France, to join a resident group of three mares in Tierpark Berlin, Germany. We measured fecal glucocorticoid metabolite (fGCM) concentrations daily in each individual from 6 days before the translocation event, to 14 days after translocation. EHV shedding was screened for all animals at Tierpark Berlin using an indirect sampling method. Following the translocation event we found significantly elevated fGCM concentrations in all animals compared to fGCM levels before the translocation event, which coincided with increased rates of EHV shedding. Our results support the hypothesis that environmental stressors induce viral reactivation in wild equids. This finding suggests that potentials stressors such as translocation and group restructuring should be considered in the management of zoological collections to reduce the risk of fatal EHV infections in novel hosts. Moreover, environmental stressors may also play an important role regarding EHV reactivation and spreading in wild equid populations.

Supplement to: Seeber, Peter A; Quintard, Benoît; Sicks, Florian; Dehnhard, Martin; Greenwood, Alex D; Franz, Mathias (2018): Environmental stressors may cause equine herpesvirus reactivation in captive Grévy's zebras (Equus grevyi). PeerJ, 6, e5422