Traveling with your horse can be one of the most fun and
exciting parts of your relationship. Whether you travel to a show
or trail ride with friends, it’s one of the ways many people enjoy
the companionship of their equine friends. Unfortunately, with
any form of travel and interaction with other horses, there is a risk
of exposure to contagious diseases. Within recent months, reports
of outbreaks of disease caused by Equine Herpes Virus 1 (EHV- 1)
have been reported in the Midwest. Understanding this virus and
how it could affect your horse is the first step to protecting him
or her from this very scary disease. EHV- 1 is a common virus
that most horses are infected with at some point in their life. As
with human herpes viruses, the virus lies dormant in lymphoid
tissue and can be reactivated during times of stress. Vaccination
of horses against EHV- 1 helps prevent infection with other strains
of EHV- 1, and can help decrease shedding of virus in respiratory
secretions if reactivation occurs.
EHV- 1 infection usually results in respiratory disease, abortion, or early neonatal death. But just like many other viruses,
there are different strains of EHV- 1. One of the strains of EHV- 1
can cause Equine Herpes Myeloencephalopathy (EHM), which
occurs when the virus infects the central nervous system. This is
a serious and sometimes fatal manifestation of EHV- 1 disease,
because the spinal cord (and occasionally the brain) are damaged. The affected horse presents with neurologic signs, including
weakness or incoordination of the hind limbs, urine dribbling,
and sometimes, impaired mental status. This manifestation of
infection can lead to very serious complications, including the
inability to rise and death.
Much research has been done in recent years to determine
why some horses develop EHM while others do not. Recent studies have found that most cases of EHM are caused by a specific
variant of the EHV- 1 virus, which resulted from a genetic mutation. This EHM variant is not currently protected against with
the vaccinations that are available to horse owners. Without the
means to prevent infection through administration of a vaccine,
it is imperative that you take precautions to decrease exposure to
the EHM variant, and to be aware of clinical signs (symptoms) in
order to administer treatment as soon as possible.
How to be proactive in protecting your horse from
EHM while traveling:
Avoid physical contact with unknown horses—especially
; ; EHV- 1 is shed in the nasal secretions even in horses that
If you touch an unknown horse, wash your hands with
soap and water before touching your horse
EHV- 1 Rears its Ugly Head
How to Protect Your Horse from EHM while On-the-Go
By Abra Foster, DVM Student (Class of 2016)
Co-authored by Dr. Sandy Taylor, DVM, PhD, Dipl. ACVIM, Purdue Large Animal Internal Medicine
Do not share equipment, water buckets, feed bins, pitch
forks, etc with other horses
Decontaminate any equipment or environment
(such as a stall) if you have to share, using a 1:10 bleach
to water solution
Upon returning to your barn, monitor your horse’s
temperature for 10 days, and call your veterinarian if the
temperature is > 102F
; ; Fever is often the first sign of possible infection and
is strongly associated with EHM infection
Keep horses that regularly travel separated from horses
in your barn that stay home
Vaccinate your horses against EHV- 1 regularly
; ; Although it does not provide protection from the EHM
variant, it has been shown to significantly reduce the viral
shedding in the event of infection and this is very impor-
tant to slowing the spread of the disease to other horses
The mechanism by which the EHM variant of EHV- 1 causes
neurologic disease is not fully understood. White blood cells
infected with the virus are believed to travel through the blood
and then infect endothelial cells (cells lining the wall of the blood
vessels) in the central nervous system. This can lead to thrombosis
(blood clots), which cuts off blood supply to the spinal cord or
brain. This leads to severe damage and results in neurologic clinical
signs. The severity of the signs will factor strongly into the prog-
nosis of the horse. Neurologic clinical signs of EHM often show
up 6-10 days after infection and will happen very suddenly. Close
daily monitoring of temperature and assessing for any neurologic
changes will be key to your proactive approach to protecting your
horse after traveling.
If you suspect that your horse has EHM, call your veterinarian immediately! The most important aspect of EHM treatment
is supportive and nursing care, which often includes intravenous
fluid therapy, nutritional support, and treating or preventing
complications associated with recumbency (being unable to rise).
Anti-viral drugs such as valacyclovir may improve the prognosis
in horses with EHM, but not all horses respond/improve with this
treatment. It is also important to administer anti-inflammatory
drugs to decrease inflammation in the central nervous system.
The majority of horses that survive EHM will show improvement
within 10-14 days of treatment.
Information is power. Although EHV- 1 infection is not completely preventable, you can take steps to help protect your horse
against EHM during your next traveling adventure. If you have
any concerns or suspect your horse has developed EHM, contact
your primary veterinarian immediately to discuss the next step.
Resources: American Association of Equine Practitioners. FAQ: Regarding Equine Herpesvirus (EHV). 2013.
Furr, Martin & Reed, Stephen. Equine Neurology. Chapter 13: Viral Diseases of the Nervous System. Blackwell Publishing, 2008.
Perkins et al. Investigation of prevalence of neurologic equine herpes virus type 1 (EHV- 1) in a 23-year retrospective analysis (1984-2007). Veterinary Microbiology. 2009: 139, 375-378.
Pusterla, Nicola & Hussey, Gisela. Equine Herpesvirus 1 Myeloencephalopathy. Veterinary Clinics of North America: Equine Practice. 2014: 30 ( 3), 489-506.