The Department of Agriculture, Trade and Consumer Protection (DATCP) has received reports of Equine Herpes Myeloencephalopthy (EHM) cases in five Wisconsin counties: Clark, Grant, Monroe, Sauk, and Vernon.

Horses at affected facilities have tested positive for equine herpesvirus-1 (EHV-1), a highly contagious virus that causes respiratory disease, abortion, and intermittent outbreaks of neurologic disease in horses. Equine Herpes Myeloencephalopthy is often fatal. Horses at facilities where EHM has been diagnosed have been quarantined. Equine herpes viruses are reportable in Wisconsin. While cases are not reported every year, it is not uncommon for outbreaks to arise this time of year, when equine events occur where horses commingle with animals from other farms.

Symptoms that should alert horse owners to the possibility of equine herpes virus infection include lethargy, decreased appetite, fever, nasal discharge, cough, weakness or incoordination, and urine dribbling. It may cause abortion in pregnant mares. Horses with any of these symptoms should be examined immediately by a veterinarian. Suspect horses should be isolated from healthy horses and tested for EHV-1.

Vaccinations are available for EHV-1 & EHV-4 which can help prevent respiratory and reproductive symptoms. Currently licensed vaccines are not labeled for the prevention of the neurologic form of EHV-1, however vaccines may assist in limiting the spread of outbreaks of EHM by limiting nasal shedding of EHV-1 and dissemination of infection. The American Association of Equine Practitioners provides risk-based vaccination guidelines for horse owners. As spring approaches, DATCP recommends consulting with your equine veterinarian on what vaccinations are recommended for your horse.

Horses that have been exposed to any infectious or contagious disease, or have symptoms of contagious respiratory infection, must not be taken to shows, competitions, clinics or public trail rides. Horse owners should also be aware that transportation of horses to these events may increase the risk of exposure to infectious organisms. While travelling with horses, taking a rectal temperature twice daily can help detect illness early. Any temperature higher than 101°F should be reported to a veterinarian. Horses returning from a show or sale should be isolated from the herd for 21 days. Since January 1, 2024, 11 other states have reported cases of Equine Herpes Myeloencephalopthy.

Both EHV-1 and EHV-4 spread primarily by direct or indirect contact with nasal secretions from infected horses. Although humans can’t be infected by EHV-1, they can aid in spreading it to their horses. Hand washing is recommended after interacting with horses. If returning to a horse farm after a show or competition, it is also to prudent to change clothes and shoes. DATCP Division of Animal Health has resources on biosecurity on our webpage.

Wisconsin Department of Agriculture, Trade and Consumer Protection
Division of Animal Health
https://datcp.wi.gov