Equine Herpesvirus (EHV) is a normally occurring, highly infectious DNA virus found all over the world in the equine population. By following vaccination and biosecurity protocols, outbreaks can be minimized and contained. Early identification and reporting of the virus is key to tracing and preventing further spread.
Currently, there is an outbreak of the neurological form of EHV-1 in Europe, which originated in Spain, that has led to the deaths of six horses. This has resulted in outbreaks in at least three other European countries and the cancellation of FEI competitions through the month of March.
What is EHV-1?
The neurologic form of EHV-1 causes what veterinarians call Equine Herpes Virus Myeloencephalopathy (EHM).
Neurological signs appear as a result of damage to blood vessels in the brain and spinal cord associated with EHV infection.
Infection with the milder form, known as the non-neuropathogenic strain, is common. By the age of two, nearly all horses have been infected with EHV-1.
Initial exposure generally occurs in foals from contact with their mothers, usually by respiratory shedding. Scientists are not entirely sure over what distance the virus can spread in this manner under typical horse management and environmental conditions.
How is it spread?
EHV-1 is contagious and spread by direct horse-to-horse contact via the respiratory tract through nasal secretions or indirectly through surfaces that have been contaminated with the virus.
Risk factors include large numbers of horses in close quarters and under the stresses of competition and travel.
The incubation period for the disease may be as little as 24 hours, but is typically 4 to 6 days. It can be longer.
Respiratory disease caused by EHV-1 is most common in weaned foals and yearlings, often in autumn and winter. Older horses are more likely than younger ones to transmit the virus without showing signs of infection.
Horses can be kept safe by implementing two strategies: biosecurity and vaccination protocols.
Implementing thorough hygiene and biosecurity protocols is important at all times, even when an outbreak has not occurred. Biosecurity and preventing the spread of disease is fresh in our minds because of the Covid-19 pandemic, and owners must now implement specific protocols at their barns for the safety of their horses. Some biosecurity steps to prevent the spread of EHV-1 include:
• Limit direct contact of your horse with others whenever possible – think equine “social distancing.” Do not use communal water buckets and avoid mixing of horses wherever possible.
• Take your horse’s temperature twice daily and report any horse with a temperature above 101.5 degrees Fahrenheit to your veterinarian immediately.
• Pay close attention for signs of respiratory or neurological disease. Clinical signs of the neurologic disease may include incoordination, hind limb weakness, lethargy, head tilt, inability to get up after laying down, and inability to maintain balance. Clinical signs of respiratory disease often include discharge from the nostrils or eyes or swelling in the throat area.
• Do not share buckets, halters, leads, bridles, or other tack between horses to prevent possible cross-contamination. Clearly label your equipment, and if you must share, make sure to scrub and thoroughly clean equipment with detergent before using it with another horse.
• Prevent people in your barn from potentially transferring the virus by washing your hands between handling different horses. Bring a change of clothes and shoes if a horse is suspected of being infected.
• If you suspect your horse may be infected or has a high temperature, immediately isolate them from the other horses at your barn and contact your veterinarian. Ideally, a potentially sick horse should be moved into a separate building or paddock, or to an isolation facility.
Making sure your horse is up to date on all their vaccines will help strengthen their immune system against potential viruses. There are vaccines available to protect against the respiratory disease and abortion-causing EHV (Rhinopneumonitis vaccine), however, there is no vaccine available for protection against the neurologic form. Some EHV vaccines can reduce nasal shedding of the disease, therefore potentially reducing transmission. Please contact your veterinarian for any questions regarding vaccinating your horse.
What to do next
If you have recently imported a horse or are planning for the arrival of a horse from any country in mainland Europe, take extra precautions by calling your veterinarian. In addition to implementing biosecurity measures in the barn, it is recommended that your imported horse receive a nasal swab and blood sample to detect the virus by PCR (polymerase chain reaction), which will identify the DNA of the virus.