A team of researchers from the University of California, Davis (UC Davis), recently tested if idiopathic headshaking in horses could be similar to a condition in humans–trigeminal nerve pain caused by the reactivation of a latent virus.

In horses the trigeminal nerve provides sensation to the face and muzzle. Similarly, in humans, the nerve is responsible for facial sensations and some motor functions including chewing and swallowing. Humans suffering from trigeminal neuropathic pain often complain of burning, itching, shock-like or tingling sensations, and shingles, a reactivation of a latent herpesvirus (varicella-zoster virus, more commonly known as chickenpox), has been implicated as a potential cause.

In horses, reactivated latent equine herpesvirus-1 (EHV-1) in the trigeminal ganglion could cause neuropathic pain similar to pain sensations experienced by people with shingles. This pain in horses could potentially result in unexplained headshaking.

Monica Aleman, DVM, PhD, Dipl. ACVIM, explained that this study investigated headshaking with no discernible physical cause, such as tooth, ear, or eye problems. "These are the ones we call idiopathic head shakers," she said. "It has been proposed that EHV-1 infection is involved in or is the cause of headshaking in horses