As of early December 2025, 60 cases of equine herpesvirus-1, or EHV-1, have been reported in horses from eight states, with most showing neurologic signs.

EHV-1 and EHV-4 are the most common of the nine EHV viruses and the ones posing the highest risk to horses. Both can cause mild self-limiting respiratory disease and abortion, but EHV-1 can also cause potentially fatal neurologic disease.

Carrier horses with no clinical signs can spread EHV to other horses. Vaccines are approved for the respiratory and abortive forms of EHV, but there’s no vaccine currently labeled for the neurologic form.

Disease spread can be mitigated by isolating and monitoring new or returning horses for at least 21 days and regularly cleaning and disinfecting equipment and surfaces.