At least three horses at a Dane County, Wisconsin boarding and training facility have tested positive for equine herpesvirus-1 (EHV-1), with one horse being euthanized as a result.

Beautiful horses
Public domain image/Dusan Bicanski

According to the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), one horse became ill in late August showing neurologic signs and was humanely euthanized.  The other two horses became ill over the Labor Day weekend and are being treated by a veterinarian.  All three horses were vaccinated in spring for rhinopneumonitis, which is caused by an equine herpesvirus.  Currently licensed vaccines are not labeled for the prevention of the neurologic form of EHV-1.

“Horses with a fever and symptoms of contagious respiratory infection should be kept at home and not taken to shows, competitions, clinics or public trail rides,” says Dr. Paul McGraw, Wisconsin’s State Veterinarian with the DATCP. Horse owners should also be aware that transportation of horses to competitions, shows and clinics may increase the risk of exposure to infectious organisms.

According to Veterinary Virology, Equine herpesvirus 1 (EHV-1) is a virus of the family Herpesviridae that causes abortion, respiratory disease and occasionally neonatal mortality in horses.

Initial spread of EHV-1 by a newly introduced horse through direct and indirect contact can lead to abortion and perinatal infection in up to 70 percent of a previously unexposed herd. Abortion usually occurs in the last four months of gestation, two to four weeks after infection of the mare. Perinatal (around the time of birth) infection can lead to pneumonia and death. Encephalitis can occur in affected animals, leading to ataxia, paralysis, and death.

See more about EHV-1 in the Merck Veterinary Manual.

Although humans can’t be infected by EHV-1, they can aid in spreading it to their horses.  Therefore, owners of affected horses should wash and disinfect their hands and change their clothes before coming into contact with healthy horses to prevent the potential spread of these infectious organisms.