Herpesvirus: What you need to know
March, 2007
Equine Herpesvirus 1:
What is the Problem?
Outbreaks of equine herpesvirus 1 (EHV-1) in different states around the country
have resulted in the sickness and death of a number of horses, cancellation of some
major annual equine events, and quarantine of certain facilities and farms. The
states mainly affected were Florida and California, but Connecticut, Rhode Island
and Wisconsin also had officially documented cases of EHV-1.
A fairly common virus, EHV-1 (also called rhinopneumonitis or "rhino")
typically causes upper respiratory infection in young horses and abortion in pregnant
mares. Unfortunately, this strain can also mutate and cause a more severe neurological
condition. Even worse, while the available vaccines provide only partial protection
against the respiratory and reproductive forms, they provide NO protection against
the form that causes central nervous system (CNS) problems.
The respiratory form of the disease can cause fever, nasal discharge, cough, lethargy,
inappetence and sometimes swelling of the legs. The reproductive form can cause
abortion, stillbirths, damage to the uterus or placenta, and sickness and death
in newborn foals. The neurologic form can cause weakness, incoordination and paralysis
in the hind legs; urinary incontinence and loss of tail tone; and other CNS signs.
What makes EHV-1 so challenging to control is that many horses are "silent
carriers" meaning they don’t show any signs of sickness themselves but are
secretly shedding the virus, especially during times of stress. In addition, the
virus can be spread by direct contact between horses, by "aerosolization"
of the virus into the air through coughing or snorting, and by "fomites,"
which include anything the virus may stick to such as buckets and tanks, fences
and walls, and shoes and hands.
What You Need to Know
What is the Solution?
Because EHV-1 is a virus, antibiotics will not work against the primary disease.
They will only help if a secondary bacterial infection occurs. So no matter which
body system the virus attacks, providing good nursing care is the best treatment.
Anti-inflammatories may be helpful to reduce fever, pain or swelling, but should
only be administered upon the advice of your veterinarian, who should be contacted
at the first sign of disease. He or she can diagnose EHV-1 by isolating the virus
from nasal swabs or by drawing blood 7 to 21 days apart and checking for a rise
in antibody titer. A complete blood cell count (CBC) is also helpful.
To prevent infection, all horses new to a facility should be isolated from the other
horses for 21 days, the longest a horse could have an active EHV-1 infection and
not show signs. Even horses returning to their barn after a show, clinic or trail
ride should be kept and handled separately for at least 2-3 days. During this time,
temperatures should be taken daily and any horses above 101.5 should be further
isolated.
Even though the vaccines currently available only offer moderate protection against
the respiratory and reproductive forms of the virus—and no protection against the
neurological form--it is still a good idea to vaccinate against EHV-1. In fact,
because the virus is difficult for the body to form antibodies against and because
there are different strains, it may be a good idea to vaccinate MORE frequently.
Talk to your veterinarian about which vaccine and when is best for your horse and
your particular situation.
Source: Equine herpesvirus 1 and 4
written by Stephen Reed, DVM and Ramiro Toribio, DVM, PhD in Veterinary Clinics
of North America 2004, Vol. 20, pages 631-642.
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