What is Equine Herpesvirus?
Equine herpesvirus, often abbreviated to EHV, is a family of equine viruses named by numbers, with EHV-1 and EHV-4 posing the most risk for domestic horses.
EHV-1 and EHV-4 most often cause respiratory disease which is usually mild and self-limiting. Both EHV-1 and EHV-4 can cause abortion. In some cases, EHV-1 can cause the neurologic form of the disease which is known as equine herpesvirus myeloencephalopathy (EHM). In extremely rare cases, EHV-4 may cause EHM.
EHM occurs as a result of virus-induced inflammation and clotting of blood vessels within the brain and spinal cord. Though the majority of horses with EHM that are treated survive, EHM can be fatal.
Horses are exposed to EHV through inhalation, direct contact with other horses or their respiratory secretions, or through aborted fetal tissue. EHV is readily transmitted on caretakers’ clothing and equipment. Following exposure to EHV, horses may develop clinical signs as soon as 24 hours though the typical onset of illness is 4-6 days. Horses can be carriers of EHV with no clinical signs and can spread the disease to other horses. Testing and quarantining affected horses is the primary way to control the disease.
Clinical Signs
- Fever
- Nasal discharge
- Swollen limbs
- Lethargy
- Neurologic disease (EHM)
- Neonatal death
- Late-term abortion
Diagnosis: EHV-1 and EHV-4 are most readily diagnosed through PCR testing of a nasal swab and EDTA blood.
Treatment: Supportive care and rest are the chief treatments. In some cases of close-contact exposure, antivirals may be recommended before clinical signs develop. Non-steroidal anti-inflammatory medications, such as phenylbutazone (Bute) or flunixin meglumine (Banamine) are used to control fever, pain, and inflammation. In some cases, antivirals, corticosteroids, and anti-coagulants are used.
Prevention: Vaccinations are available to help prevent abortion and decrease the signs and severity of the respiratory form of EHV-1 and EHV-4. There is currently no vaccine labeled for the prevention of the neurologic form of EHV (EHM). The best method of protection is always to maintain current vaccinations on all horses on your property, to quarantine and temperature check new horses arriving on premises, and to follow good biosecurity protocol when travelling with your horse.
Biosecurity: EHV is spread via aerosolized particles and droplets from nasal discharge and fetal tissue or from contaminated surfaces including people, clothing, feed and water, equipment, and stalls. Isolation is critical to preventing spread of the virus. Horses with EHV must be physically separated in a different airspace from healthy horses. Proper biosecurity measures while travelling include twice daily temperature checks, and limiting exposure to shared spaces including wash racks and water or feed troughs.