EQUINE HERPES VIRUS
The Equine Herpes Viruses are found throughout the horse population and latent infection and
in apparent carriers are common in adult horses so that most horses are latently infected and
have the potential to shed virus if it re-emerges. Re-emergence can occur at times of stress
when the immune system is suppressed. The viruses can evade the immune system and infect
horses that have been vaccinated.
Types of Virus:
There are four main types of EHV but subtypes 1 and 4 are the most significant with regard to
equine disease.
EHV1 causes abortion and myeloencephalitis (neurological disease). Specific strains of EHV1
are responsible for neurological disease. Recovery from neurological disease can be complete;
a small percentage of cases have permanent, neurological deficits, and some cases are fatal.
EHV4 causes acute respiratory disease.
Transmission:
The virus is transmitted by direct and indirect contact (ie via peoples’ clothing, equipment etc)
with infectious nasal secretions or material from abortions.
Vaccination:
Although possible, immunity is short-lived, lasting only 2-4 months. In addition it is not 100%
protective and may only serve to reduce the severity of an infection and the level of viral
shedding during an infection. Vaccination is required at 3, 5, 7 & 9 months of pregnancy to
prevent abortion. Non-broodmares require a booster every 6 months following completion of
the primary course.
The strains of EHV1 that cause neurological disease are unfortunately particularly unresponsive
to vaccination.
Breeding:
The diminished resistance to disease found in pregnant mares can result in the virus appearing
in the blood and may result in transplacental infection of the foetus. The result may be abortion
or an infected foal being born.
Horses that are known to have been affected:
It is worth remembering that most horses are latently infected. Horses that have been affected
with neurological disease may have permanent deficits. To avoid re-emergence of virus from
latently infected individuals it is important to avoid times of stress and immunosuppression (NB
pregnancy!).
Zylexis is an injectable immunomodulator which can be useful in times of stress (eg
travel/competition/mixing of horses) and may help reduce the severity and duration of disease.
Please enquire for further details.
Coach House Vets Ltd. Burlyns, East Woodhay, Newbury, Berkshire, RG20 0NU
T: 01635 254544 e: reception@coachhousevets.com www.coachhousevets.com