Equine Herpesvirus-1 has been reported in several states causing alarm in equine communities. EHV-1 is highly contagious among horses and can cause a variety of ailments in equines, including respiratory disease, abortion in broodmares, and myeloencephalopathy (EHM, the neurologic form).Here are the basic facts you should know about Equine Herpesvirus:
Overview of Herpesvirus
Herpesviruses are a species-specific family of DNA viruses. They are characteristic because of their ability to cause life-long infection by becoming latent. The virus is reactivated in times of stress, such as shipping, competition, etc. This results in re-infection and transmission of the virus to susceptible hosts. Herpesviruses cause disease by damaging a host’s blood vessels.
Herpesvirus in the Horse
Herpesvirus is common worldwide in the horse. A majority of the time the virus is dormant and does not cause illness. The most common sign of Herpesvirus is respiratory disease. While there are 5 subtypes of Equine Herpesvirus (EHV), 3 are considered health risks for horses (EHV-1, EHV-3, and EHV-4)
Equine Herpesvirus Myeloencephalopathy (EHM)
Infection with a neuropathogenic strain of EHV-1 causes neurologic disease by damaging the blood vessels of the brain and spinal cord. Altered blood flow injures the tissues, impairing their ability to function normally.
Typical signs of EHM:
The virus is shed in respiratory secretions, typically via coughing and snorting, and infected aborted fetuses and fetal membranes. Horse to horse contact is the most common way the disease is transmitted, but indirect transmission via contaminated lead ropes, tack, buckets, trailers, and people (hands and clothing) also occurs.
Polymerase Chain Reaction (PCR) is a test that detects the viral DNA in the blood or on a nasal swab. It can also be performed on neural tissues to confirm the diagnosis during a post-mortem examination. An ELISA test measures the antibodies to the virus in the blood. The levels should be measured 2-3 weeks apart.
Treatment is primarily directed to relieve symptoms, including anti-inflammatories. In some cases antiviral drugs may be used.
Biosecurity is essential in order to prevent horses’
exposure to the virus:
Vaccinations are recommended. Commercial vaccines for EHV-1/4 are available, but are not labeled to prevent the neurologic form of the disease
Take Home Message
Herpesvirus is common world-wide and causes respiratory, abortion and occasionally neurologic signs. The key to prevention is appropriate vaccination and management. Horse owners should consult with their local veterinarian for recommendations on an appropriate vaccination schedule and the risk in their area. For additional information, we recommend these resources:
Equine Herpes Virus – AAEP