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January 14, 2026 - Equine Herpesvirus-1 in Alberta

Staying ahead of a silent threat through symptom recognition and swift response.

Equine Herpesvirus-1 (EHV-1) is an equine virus that can cause three main problems: respiratory illness, abortion in pregnant mares, and in some cases a neurological disease called equine herpes myeloencephalopathy (EHM). Recently confirmed EHM cases in the province have become a harrowing reminder for many producers to always act on the side of caution. Equine Herpesvirus is found worldwide and the outbreaks resulting in EHM have been on the rise. While there are nine equine herpesviruses that affect horses, EHV-1 and EHV-4 are the most common in Canada and the U.S. 

EHV can be transmitted both directly and indirectly between horses. As a resilient virus, it can survive in the environment under typical conditions for up to seven days. While humans are unable to contract the virus, we can be key transmitters of it between horses through contaminated clothing, hands, and equipment. 

Producers can stay ahead of the virus and be on the watch for these symptoms: 

• Fever is often the earliest sign. If a horse has a body temperature higher than around 38.5 degrees Celsius, it can be reason for concern. The fever peaks once on days one to two of infection and again on days six to seven. 
• Respiratory signs include discharge from the nasal cavities and eyes, cough, lethargy, and reduced appetite. 
• Abortion, mainly in late term in pregnant mares. Abortions can happen even when the mare shows only mild or no respiratory signs. Pregnant mares with EHV-1 can experience abortion around seven months or later, but in rare cases it has been documented as early as four months. 
• Neurologic signs are typically exhibited once the virus has developed into EHM. Ataxia/weakness, stumbling, hindlimb weakness, reduced tail tone, dribbling urine, and inability to stand in severe cases all point to a neurological issue. Neurologic cases are the most serious and may require euthanasia if severe. 

If you suspect your horse has contracted an EHV virus, it is critical to follow key steps to ensure you limit the spread. These steps include: 

1. Isolate the suspect horse by moving it away from other equine species and limit access to only those essential for treatment and recovery. While you may be unsure if your horse has contracted EHV, it is important to treat any fevered or coughing horse as infectious until proven otherwise. Rapid response and isolation reduces the spread.  
2. Calling your veterinarian for assistance in clinical controls such as fever control and support care. They’re here to help you and you shouldn’t be managing this virus alone. The vet can also collect samples for diagnosis like a nasal swab for PCR and blood samples for virus detection. The testing will be completed by a trusted diagnostic lab.  
3. Starting biosecurity measures with using dedicated clothing and boots for the isolated horse, washing hands between handling horses, disinfecting tack and equipment, limiting movement of people and animals on/off the property, and documenting those who do visit. As you would do with a sick family member, cleaning and disinfecting high traffic areas. In this case that means trailers and stables. 
4. Quarantining and movement restrictions of the infected horse. It is critical to follow your veterinarian’s and provincial guidance on quarantine length. Such that any movement of exposed horses should be halted. Alberta’s Office of the Chief Provincial Veterinarian (OCPV) issues direction. This could be reporting any movement of the horse from the isolated site and ensuring those proper movement controls are in place. 

If EHV is suspected or confirmed on your farm, notify your veterinarian and follow instructions from the OCPV. 

According to the OCPV, recent case confirmations in Alberta show that even vaccinated horses can be affected, making early detection and strict biosecurity essential to the health and safety of other equine herds. 

EHV is a real and recurring threat to Alberta’s horse community. Watch temperatures daily, isolate and call your vet immediately if you see fever, respiratory or neurologic signs, and follow provincial reporting and quarantine directions. Quick action and solid biosecurity are the best ways to stop an outbreak from becoming a tragedy.