Written By: Dr. Lisa Nesson
It’s the time of year when a few cases of equine herpes virus present around the US. As always, biosecurity is a very important part of traveling with your horse. Please read on to learn more about EHV-1 and basic biosecurity.
EHV-1: Clinical Basics
EHV-1 stands for Equine Herpes Virus 1, which describes the virus. EHV causes four conditions: respiratory disease, abortion, neonatal disease, and neurologic disease (EHM). EHM stands for Equine Herpes Myeloencephalopathy, which describes the neurologic disease caused by EHV-1. Just because the horse is infected with EHV-1 does not mean that your horse will come down with EHM. Additionally, because EHV-1 is endemic in the equine population, horses can be positive for EHV-1 but not show any signs of the clinical disease.
Transmission of EHV-1 can happen in a multitude of ways, including inhalation, contact between horses, contact via fomites (via water bucks, equipment, etc), and ingestion. The initial fever, which begins following a four to seven day incubation period, is a low grade fever, which will be difficult to notice unless closely monitoring your horse’s temperature. The second spike is around seven days after the initial fever, and will be a much higher temperature – your horse may appear depressed or lethargic, but the best way to assess a fever is to take a rectal temperature. Neurologic signs develop seven to twelve days after the second fever.
After the fever, the affected horse may recover, and appear normal, or it may go on to develop EHM, which will occur after seven to twelve days. The horse infected with EHM may appear ataxic, or uncoordinated, dripping urine, and unable to pass manure. These horses may have a normal temperature at this time. Older horses and horses with compromised immune systems may be more susceptible to develop EHM following the EHV-1 virus.
Some neurologic symptoms to watch out for include hind leg ataxia (your horse will struggle using their hind legs), vasculitis (swollen or distended blood vessels) and abnormal or lack of urination. Often, the first symptom you notice is the high temperature as this will be the first indication of the virus. When a horse does have EHV-1, he/she will spike an initial temperature, return to a normal range, and then spike a second fever. Neurologic symptoms won’t develop until seven to twelve days after the fever. To ensure early detection of EHV-1, monitor your horse for these clinical signs of disease, and keep a log of twice daily temperature readings. Immediately report any temperature over 102°F to your veterinarian.
Protecting your horse from EHV-1
The best way to protect your horse when attending an equine event or visiting outside barns is to practice proper biosecurity. Compliance with basic biosecurity practices is essential as it is an important factor in reducing exposure to, and spread of, contagious equine diseases. To reduce risk of spreading EHV-1 to your horse and other horses in your barn, ensure that you:
Limit horse-to-horse contact (keep visiting horses separate from barn herds)
Limit horse-to-human-to-horse contact (avoid touching horses other than your own)
Avoid use of communal water sources (bring your own water buckets to events)
Avoid sharing of equipment unless thoroughly cleaned and disinfected between uses
If you have any additional questions, please reach out to our office or your own local equine veterinarian.