Equine herpesvirus type I (EHV-1)
S0071 - Qualitative detection of equine herpesvirus type I by polymerase chain reaction.
included in P0013 - equine
respiratory panel, in P0014 -
equine neurological panel and in
P0024 - equine breeding panel.
herpesvirus 1 (EHV-1) is a major cause worldwide of epidemic
abortion, perinatal mortality, respiratory disease and
neurological disorders in horses. EHV-1 is a member of the
Alphaherpesvirinae subfamily that also includes herpes simplex
virus (HSV) types 1 and 2 and varicella zoster virus (VZV). As
with other herpesvirus infections, lifelong latency of the virus
in the nervous system of the host occurs, and periodical
reactivation of the virus can cause new outbreaks (Slater et
primary infection generates a humoral response and the
production of neutralizing antibodies, infected animals do not
develop long lasting protection against EHV-1 and remain
susceptible to re-infection throughout life, although the
severity of secondary infection is reduced.
respiratory infection is the most common manifestation of EHV-1
infection. Commonly, young horses (weanlings, yearlings, and 2
year olds) have depression, poor appetite, nasal discharge and
cough. If young horses are housed or pastured together, many
horses in the herd may experience disease from which they
recover uneventfully. Disease may be mild or unapparent in older
horses. Neurological signs occur infrequently as a result of
EHV-1 infection; however, outbreaks of neurologic disease
associated with fever, nasal discharge and cough have been
reported in the USA and elsewhere. Neurologic signs may include
incoordination that can progress to an inability to stand.
Horses may be unable to urinate or may dribble small volumes of
urine. Horses may have difficulty producing manure. Sometimes
the neurologic signs are accompanied by cellulitis (inflammation
or swelling of the limbs) and petechiae (small hemorrhages on
transmission of EHV-1 from the mare to the foal is one of the
major causes of spreading infection. Lactating mares having the
potential to infect their suckling foals within 30 days of age.
These foals can then spread EHV-1 to other foals within their
group prior to and throughout weaning. The weaning process
involves the separation of the foal from its dam and intensive
human contact, placing foals under stressful conditions, a
contributing factor in the reactivation of EHV. The virus can
then spread through contact with other foals. Farm management
practices such as routine handling of mares and foals and the
mixing of paddock groups can also encourage the introduction and
spread of EHV.
mares are still able to transmit EHV-1 to their unweaned
unvaccinated foals, despite having received three vaccinations
during the previous gestation. The vaccine may result in a
reduction in the period of excretion of the virus, however it is
not sufficient to prevent EVH-1 infecting new foals.
of EHV-1 abortion can only be made by postmortem examination of
the fetus. EHV-1 is readily isolated from a wide range of
tissues in aborted fetuses. Infection of endothelial cells in
the uterus and placenta plays a significant role in the
pathogenesis of abortion and in dissemination of the virus.
Testing the mare's serum for antibodies is of little value,
because virus-infected foals can be born from mares that show no
evidence of recent antibody activity, and noninfected foals can
be born from dams that do show recent antibody rises.
can be isolated from pharyngeal or nasal secretions by culture.
Isolation of the virus from respiratory secretions strongly
suggests that the virus is the cause of the disease. However,
this method is slow and has low sensitivity. Molecular detection
by PCR can identify the virus in pharyngeal or nasal secretions.
Blood cells can also be tested by PCR, with detection of the
virus indicating that the horse is currently or has recently
been viremic. However, it is important to note that a negative
PCR test does not rule out EHV-1 as the cause of the disease, as
viremia is intermittent.
Help confirm the disease causing agent
Shorten the time required to confirm a clinical
diagnosis of EHV-1 infection
Help ensure that horse populations are free of EHV-1
Early prevention of spread of this virus
Minimize personnel exposure to this virus
Safety monitoring of biological products that derive
Slater, J. D., Borchers, K., Thackray, A. M. and Field, H. J.
(1994) The trigeminal ganglion is a location for equine
herpesvirus 1 latency and reactivation in the horse. J. Gen.
Virol. 75: 2007–2016.
Nasopharyngeal swab, or 0.2 ml whole blood in EDTA (purple top)
or ACD (yellow top) tube, or 0.2 ml CSF, or 0.2 ml fresh, frozen
or fixed tissue.
Contact Zoologix if advice is needed to determine an appropriate specimen type for a specific diagnostic application. For specimen types not listed here, please contact Zoologix to confirm specimen acceptability and shipping instructions.
specimen types, if there will be a delay in shipping, or during
very warm weather, refrigerate specimens until shipped and ship
with a cold pack unless more stringent shipping requirements are
specified. Frozen specimens should be shipped so as to remain
frozen in transit. See shipping
instructions for more information.
2 business days