Equine Herpesvirus

8/18/2019 Equine Herpesvirus

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Equine

Herpesvirus (EHV)Myeloencephalopathy

A Guide To Understanding theNeurologic For o! EHV "n!ection


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#hat is EHM$

Equine herpesvirus myeloencephalopathy

(EHM) is another name for the neurologic disease

associated with equine herpesvirus (EHV) infec-

tions. Neurological signs appear as a result of

damage to lood vessels in the rain and spinal

cord associated with EHV infection. !nterferencewith the lood supply leads to tissue damage and

a susequent loss in normal function of areas in

the rain and spinal cord.

Neurological signs appearas a result of damage toblood vessels in the brainand spinal cord associatedwith EHV infection.

#hat are the equine herpesviruses$

"o date# nine EHVs have een identified world-

wide. "hree of these$EHV-%# EHV- and EHV-

'$pose the most serious health riss for domes-ticated horses and can have significant economic

impacts on the .*. equine industry.

+ EHV%&' ,an cause four manifestations of

disease in horses# including a neurologi-

cal form# respiratory disease# aortion# andneonatal death. EHM is most often due to

mutant or neuropathogenic strains of EHV-%#

so called ecause of a particular mutation in

the genome.

+ EHV%' ,auses a venereal disease calledequine coital eanthema that affects the

eternal genitalia.

+ EHV%' ,auses a nonfatal upper respiratory

tract disease in foals and is uncommonly

associated with aortion and rarely with

neurologic disease.


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Ho* coon are EHV%& in!ections$

y / years of age# almost all horses have een

infected with EHV-%. "he initial eposure gener-

ally occurs in foals from contact with their dams.

"he virus can then ecome latent# or inactive# in

the horse0s ody# setting up a carrier state that

is life-long. Horses of any age that are carriers ofEHV-% do not show any eternal signs of disease

when the virus is in a latent form. "he virus can

e reactivated during times of stress# such as

strenuous eercise# long-distance transport# or at

weaning.

"ransmission of EHV-%

1atently

!

n

1a


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!nfection of 2oal34dult Horse

!nfection of 5ther 2oals34dult Horses

"he transmission of EHV-% occurs after an eposure to anadult horse or foal with an active EHV-% viral infection. "hiseposure generally occurs via respiratory shedding of the

virus. "he infected adult horse or foal may or may not eehiiting clinical signs of disease.


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#hy should " +e concerned

a+out EHV%&$EHV-% is the primary cause of EHM. !n recent

years# there has een a mared increase in the

numer of EHV-% cases# especially EHM# reported

in the nited *tates. "here have also een several

outreas of EHM at large horse facilities andevents$at racetracs# horse show grounds#

veterinary clinics# and oarding stales. "he large

numer of horses that can e eposed on such

premises and the serious nature of the disease

have caused significant concern within the animal

health community and the .*. horse industry.

The virus can be reactivatedduring times of stress, such

as strenuous exercise, long-distance transport, or atweaning.

2urthermore# these recent occurrences of

EHM appear to meet the criteria of an emergingdisease. 4 disease is considered to e 6emerging7

when it satisfies at least one of three criteria8

%. "he disease is identified for the first time in a

region or country9

/. 4 disease changes in severity# type of animal

that can e infected# or other changes in

pathogen ehavior9 or

&. "here is a change in geographic range of a

disease or in its incidence within a range.

EHM liely meets the second criterion of an

emerging disease# as the recent EHV-% outreas

seem to e associated with a change in the sever-

ity and ehavior of the virus. !t is possile that the

reporting of EHV-% cases has increased# rather

than an actual increase in the numer and sever-ity of cases9 however# more data are needed to

mae such a distinction.


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Ho* is the virus spread$

"he most common way for EHV-% to spread

is y direct horse-to-horse contact. "his virus

is shed from infected horses via the respiratory

tract or through direct or indirect contact with

an infected aorted fetus and fetal memranes.

Horses may appear to e perfectly healthy yetspread the virus via the secretions from their

nostrils.

!t is important to reali:e that EHV-% can also

e spread indirectly through contact with physi-

cal o;ects contaminated with infectious virus.Eamples of such o;ects include8

+ "ac#

+


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#hen should " suspect y horse ight

have EHM$*igns of EHM include8

+ 2ever preceding neurologic signs

(either in a

horse diagnosed with EHM or in horses that

have een eposed to a horse diagnosed with

EHM)#

+ >ecreased coordination#

+ rine driling#

+ 1oss of tail tone#

+ Hind lim weaness#

+ 1eaningagainst a wall or fence

to maintain

alance#

+ 1ethargy# and

+ !naility to rise.

Horses may appear to be perfectly healthy yet spread

the virus via the secretions from their nostrils.


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Ho* is the disease diagnosed$

>iagnostics your veterinarian might perform

for

a live horse include8

+ Nasal swa collection for

laoratory eami-nation and detection of virus y polymerase

chain reaction (=,?) assay or y

virus isola-

tion9 and

+ lood collection to detect the

virus y =,?

assay or y virus isolation. lood samples

should e collected / to & wees apart for

levels of antiodies specific to EHV-%.

!deally# your veterinarian will collect oth nasalswa and lood samples to optimi:e arriving at a

diagnosis.

>iagnostics your veterinarian might perform

for

a deceased horse include8+ Necropsy eamination of a

horse with neu-

rologic disease that dies or has to e eutha-

ni:ed# or necropsy eamination of an aorted

fetus3fetal memranes. Necropsy provides animportant means of confirming the presence

of EHV-% disease.

"s there a treatent !or EHM$

"he standard form of care for EHM is primarilysupportive. "reatments may include intravenous

fluids or anti-inflammatory drugs. 4ntiiotics may

e used to treat a secondary acterial infection if

one develops9 however# antiiotics have no effect

on the equine herpesvirus itself. 4ntiviral drugs

have also een used to treat EHM

cases. ?esearch

on the efficacy of these drugs# their cost effective-

ness# and the optimal dosing regimen for EHM is

still underway.


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Ho* can " prevent EHV%&, the priary

cause o! EHM, !ro spreading to otherhorses$

"here are many steps you can tae to help

prevent the spread of EHV-%.

+ *top horse movement

if your animals may einfected with EHV-

%. "his is the most

important first step

horse owners can tae.

Horses should neitherenter nor leave a prem-

ises where EHM has

een diagnosed until

cleared y the veterin-

arian.

+ >o not allow horses

eposed to EHM

case(s) to have contact

with uneposed horses

on the premises.

+ !solate sic horses.

Horses that have

aorted or shown signs

of fever# respiratory

disease# or neurologic

disease should eseparated from healthy horses. !deally# the

sic horse(s) should e moved into a sepa-

rate uilding or paddoc on the premises# or

e transported to a veterinary hospital with an

isolation facility.

+ >o not share equipment among

horses on the

facility. *ince this virus can e spread from

horse to horse via contaminated o;ects such

as water3feed ucets or ridles# equipment


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-an " prevent EHM *ith vaccines$

Vaccines eist to control the respiratory and

aortion manifestations of EHV-%9 however# the

currently licensed vaccines are not laeled for

the prevention of EHM. niversity and private

researchers are looing into several eisting vac-

cines to determine if they protect against EHM. New vaccines for EHM are also eing studied.

ince this virus can be spread from horse to horse via con-taminated ob!ects such aswater"feed buc#ets or bridles,e$uipment should not be

shared among horses.

Use!ul .esources

2or more information related to EHV# EHM# and

iosecurity# please refer to the following docu-

ments and epartment of

4griculture

(*>4)

*>484=H!*8V*8,E4H. /@@A. Equine Her-

pesvirus Myeloencephalopathy8 Mitigation

Eperiences# 1essons 1earned#and 2uture

Needs. NBC//.@D@A. http833www.aphis.usda.

gov3vs3nahss3equine3

+ *>484=H!*8V*8,E4H8,E!. Emerging

4nimal >isease Notice. /@@D. Equine Herpes

Virus Myeloencephalopathy8 4

=otentially

Emerging >isease.

http833www.aphis.usda.gov3vs3ceah3cei3taf3emerging diseasenotice.files3ehv.pdf

+ *>484=H!*. iosecurity$the ey to

eep-

ing Four Horses Healthy.


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+ niversity of ,alifornia ,enter

for EquineHealth (,EH)

http833www.vetmed.ucdavis.edu3ceh3topics.htm

+ 4merican 4ssociation of Equine

=ractitioners

(44E=)http833www.aaep.org3controlGguidelinesGnon-

memer.htm

http833www.aaep.org3vaccinationGguidelines.

htm

+ !owa *tate niversity iological?is Manage-

ment (?M)

http833www.cfsph.iastate.edu3?M3equinere-

sources.htm

http833www.cfsph.iastate.edu3?M3disinfects.

htm

For More "n!oration

"o find out more aout EHM# please contact8

*>44=H!*-V*-,E4H N??, uilding# M.*. /ED

/%C@ ,entre 4venue

2ort ,ollins# ,5 A@C/I-A%%D

(JD@) 'J'-D@@@

E-mail8 N4HM*Kaphis.usda.gov

http833nahms.aphis.usda.gov

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To file a complaint of discrimination, write USDA, Director, Office

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Mention of companies or commercial products does not imply

recommendation or endorsement by the USDA over others not men-

tioned. USDA neither guarantees nor warrants the standard of any

product mentioned. Product names are mentioned solely to report

factually on available data and to provide specific information.

Issued December 2008


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United States Department of Agriculture

Animal and Plant Health Inspection Service


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Equine Herpesvirus

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