Once a horse is infected with equine herpesvirus-1 (EHV-1), the dormant virus resides in the horse's nervous system, where it can reactivate when the horse's immune system is compromised by stress or illness.

Nicola Pusterla, DVM, PhD, Dipl. ACVIM, and his colleagues at the University of California, Davis, wondered if stress caused by transporting horses would reactivate a latent infection. They tested 302 healthy horses imported from Europe and quarantined at the UC Davis facility for EHV-1.

Typically a horse's trip from a European stable to their new home in the United States requires about 12-14 days and includes a plane ride and quarantine.

"That's a lot of stress for a horse," Pusterla said, noting the research team expected to see positive test results