EVA

EQUINE VIRAL ARTERITIS

A MANAGEABLE PROBLEM

UNITED STATES DEPARTMENT OF AGRICULTURE

ANIMAL AND PLANT HEALTH INSPECTION SERVICE

PROGRAM AID NO. 1566
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and

activities on the basis of race, color, national origin, sex, religion, age, disability, political

beliefs, sexual orientation, or marital or family status. 

(Not all prohibited bases apply to all programs.) Persons with disabilities who require

alternative means for communication of program information (Braille, large print, 

audiotape, etc.) should contact USDA’s TARGET Center at (202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write 

USDA, Director, Office of Civil Rights, 

Room 326-W, Whitten Building, 

1400 Independence Avenue, SW, Washington, DC 20250–9410 

or call (202) 720–5964 (voice and TDD). 

USDA is an equal opportunity provider and employer.

Mention of companies or commercial products does not imply recommendation or 

endorsement by USDA over others not mentioned. 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 April 2001

Photo credits:

The horse images on the front cover, page 2 and 3, and the image of the virus vaccine 

materials on p.8 were taken by Bob Langrish and are reproduced by permission. The photograph of the depressed horse on p. 6 was taken by coauthor Peter Timoney, of the University

of Kentucky, and is reproduced by permission. On p. 8, the image of the male horse was

taken by Gemma Giannini and that of the female horse, by Martha Bell; both shots are

reproduced by permission. All these images remain under copyright held by the 

photographers themselves.

EVA

EQUINE VIRAL ARTERITIS

A MANAGEABLE PROBLEM

1 Dr. Timoney is Director and Frederick Van Lennep Chair in Equine Veterinary Science at

the Maxwell H. Gluck Equine Research Center, Department of Veterinary Science,

University of Kentucky, Lexington, KY 40546. He can be reached via the Internet at 

ptimoney@ca.uky.edu or by telephone at (859) 257–1531.

2Dr. Cordes is a Senior Staff Veterinarian with the National Animal Health Staff, Veterinary

Services, Animal and Plant Health Inspection Service, U.S. Department of Agriculture, 4700

River Road, Riverdale, MD 20737. He can be reached via the Internet at

Timothy.R.Cordes@usda.gov or by telephone at (301) 734–3279.

3Dr. McCollum is a professor in equine viral diseases at the Maxwell H. Gluck Equine

Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY

40546. He can be contacted by telephone at (859) 257–3620.

Peter J. Timoney, M.V.B., M.S., Ph.D., FRCVS1

Timothy R. Cordes, D.V.M.2

William H. McCollum, M.S., Ph.D.3
2 3

T ABLE OF C ONTENTS

Introduction

Facts and Fiction About EVA

Geographic Distribution of Equine Arteritis Virus

Clinical Outcome of Equine Arteritis Virus Infection

How Equine Arteritis Virus Is Spread

Persistent Equine Arteritis Virus Infection in the Stallion

Economic Significance of EVA

How To Confirm a Diagnosis of Equine Arteritis Virus Infection

Preventing the Spread of Equine Arteritis Virus

Immunization Against EVA

Conclusions

Acknowledgments

Suggested Readings

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In the past 15 years, few equine

diseases have stimulated more

interest or gained greater international notoriety than equine viral

arteritis (EVA). 

The disease was thrust into the

limelight of industry attention 

following a 1984 epidemic on a

large number of Thoroughbred

breeding farms in Kentucky. No

outbreaks of EVA had previously

been reported in Thoroughbreds 

in North America. At the time,

many people feared that a strain 

of the causative agent, equine

arteritis virus (EAV), had emerged

that was likely to spread within

the largely antibody-negative

Thoroughbred population, causing

disease and extensive outbreaks 

of abortion. The international

community took the threat 

posed by EVA so seriously that it

placed major restrictions on the

movement of horses from the

United States. Many of these

restrictions are still in force. EVA

remains a considerable impediment to international trade in

equids and semen.

In contrast to how EVA has

been regarded internationally, the

U.S. horse industry has traditionally attached relatively little significance to this disease. Over the

past several years, however, the

American Horse Council,

American Association of Equine

Practitioners, and United States

Animal Health Association have

stressed the importance of controlling EVA at the national level.

Their efforts have been hampered

by the lack of awareness of the

disease and its potential economic

consequences among most sectors

of the Nation’s horse industry.

Recent findings from the U.S.

Department of Agriculture’s

(USDA) National Animal Health

Monitoring Systems Equine ’98

Study have confirmed that the

great majority of those surveyed

had little if any knowledge about

EVA itself, let alone why it should

be prevented or how to do so.

This brochure and companion

video, produced and directed by

the USDA’s Animal and Plant

Health Inspection Service

(APHIS), aim to educate you—

the horse owners and breeders of

the United States—about EVA.

Your involvement and support are

critical to the effectiveness of any

industry-driven disease-control

program. We hope you will use

these materials to increase your

general awareness of EVA, gain a

clearer understanding of its true

4

I NTRODUCTION

equine 

viral

arteritis 

equine 

arteritis 

virus

EAV vs EVA

is the virus that 

causes

EAV

EVA

veterinary medical and economic

importance, and above all, recognize that much of what has been

said about this disease since 1984

was misinformation. Based on

what is currently known about EVA

and how to prevent it, spread of

the disease can be controlled. To

be successful, however, a control

program must be a cooperative

effort involving members of the

horse industry, private-sector veterinarians, and Federal and State

animal health officials.

5

FACTS AND FICTION

ABOUT EVA

Few equine diseases have been

the subject of more misinformation or misperception than EVA.

It is an acute, contagious viral 

disease known to affect horses

and other members of the equid

family only. EVA is not transmissible to humans or other domestic

species. Like influenza and

rhinopneumonitis, it is considered

primarily a viral infection of the

equine respiratory tract.

Contrary to the opinion of

some at the time, the 1984 epidemic in Kentucky was not the

first in North America or elsewhere. The veterinary literature

details outbreaks of a clinically

indistinguishable disease in

Germany and Great Britain in the

latter part of the nineteenth century. The first virologically confirmed outbreak of EVA in the

world occurred on a Standardbred

breeding farm near Bucyrus, OH,

in 1953. Little concern was

expressed at the time or indeed

over the subsequent 30 years in

spite of the fact that the virus had

been shown to be capable of causing contagious respiratory disease

and abortion in mares.

In contrast to the misperception that prevails in some coun-
6

• fever

• loss of

appetite

• depression

• skin rash, 

often localized to the

cheeks or sides of

the neck but sometimes all over the

body

• nasal 

discharge

• conjunctivitis

• abortion

• pneumonia 

or pneumonia

with enteritis in

very young foals

SIGNS OF EVA

• swelling, most notably

of the legs, scrotum,

sheath or mammary

glands or other dependent parts of the body

tries, EVA is not a disease that

occurs primarily in the United

States. Nor is the causal agent,

EAV, particularly limited in its distribution in horse populations

throughout the world.

Considerable confusion still

exists over the incidence of outbreaks of EVA and the clinical outcome in cases of naturally acquired

infection with the virus. In spite of

its relatively widespread global distribution, EAV is seldom associated

with outbreaks of disease in susceptible populations of horses or

other species of equids. Detailed

investigation of outbreaks of EVA

over the years has confirmed that

the vast majority of cases of acute

infection with EAV are asymptomatic. That is, most infections are

not associated with the development of any observable clinical

signs of disease. There are indications, however, that the incidence

of EVA has increased over the past

10–15 years, due in part to greater

industry awareness of the disease,

more widely available laboratory

capability to diagnose this infection, and continued expansion in

international trade in horses 

and semen.

Confusion also prevails over the

veterinary medical importance of

EVA. First, it should be emphasized that most horses naturally

7

infected with EAV display no 

visible signs of disease. The term

EVA refers to a specific disease

syndrome—a particular set of

clinical signs that certain horses

or other equines acutely infected

with EAV may develop. The term

is not applicable to cases of acute

EAV infection where there is no

clinical evidence of disease.

Much misinformation about

the medical significance of EVA

can be traced back to reports in

the earlier veterinary literature

that describe severe disease with a

case-fatality rate as high as 

40–60 percent, even in older 

horses. What is frequently not

realized is that these descriptions

refer to infection in horses with an

experimentally derived variant of

the virus isolated in 1953. They do

not represent the type and severity

of clinical disease observed in field

outbreaks of EVA. Mortality is very

infrequent in the field. Mortality

has been reported in neonatal

foals congenitally infected with

the virus and, uncommonly, in

foals up to a few weeks of age.

The vast majority of animals

affected with EVA make total clinical recoveries. In the 40–50 years

since EVA was first identified, no

naturally occurring, highly pathogenic strains of the virus have

been reported or isolated.
8

THE MOST COMMON MEANS OF EAV TRANSMISSION

respiratory system

reproductive 

tract male female

The virus can be

transmitted via

fresh-cooled or

frozen semen

used in artificial

insemination.

BY BREEDING—

Stallions and mares

acutely infected with EAV

can also pass the virus to

their breeding partners.

This is the only route of

transmission of the virus

by the persistently infected carrier stallion.

across the placenta

BY AIR—The respiratory secretions of horses acutely infected with 

EAV carry large quantities 

of the virus

BY MARE TO UNBORN FOAL—

EAV can pass across the placenta

from an infected mare to the foal in

her uterus.

GEOGRAPHIC

DISTRIBUTION OF EAV

EAV is distributed in various

horse populations throughout the

world. It has been reported from

countries in North and South

America, Europe, Africa, Asia,

Australia, and New Zealand.

Outbreaks of EVA, though relatively infrequent, are often associated with the movement of horses

or shipment of semen.

Widespread dissemination of the

virus can occur on breeding farms

and at racetracks, sales, or horse

shows, where horses are closely

congregated. The global distribution of EAV has been and continues to be influenced significantly

by the international movement of

stallions that are carriers of the

virus and by the shipment of

infective, fresh-cooled or frozen

semen.

The prevalence of EAV infection differs considerably both

among countries and among particular horse breeds in the same

country. Various serological surveys carried out in the United

States have shown that infection

with EAV can be endemic in some

breeds (e.g., Standardbreds) but

not in others (e.g., Thoroughbreds

and Quarter Horses). There is no

evidence, however, that different

9

breeds vary in their inherent susceptibility to infection with EAV.

CLINICAL OUTCOME

O F EAV INFECTION

EVA is principally a disease of the

respiratory system that can affect

horses of any age. Importantly,

most horses that are naturally

exposed to EAV develop no signs

of disease and are considered

asymptomatically infected with

the virus. The clinical outcome

following infection with EAV is

influenced by a variety of virus,

host, and environmental factors.

Severity of disease is likely to be

greater in very young or old horses

and in debilitated animals.

In cases where illness develops, the incubation period is 

usually 3–7 days but can be

longer. Clinical signs vary in

range and severity. Affected animals may exhibit some or most of

the following:

■ Fever;

■ Swelling (edema), most notably

of the legs, scrotum, sheath or

mammary glands or other dependent parts of the body;

■ Loss of appetite (anorexia);

■ Depression;

■ Nasal discharge, initially watery

(serous) but frequently becoming

mucoid later;
10

Equine arteritis virus is found

in various horse populations

throughout the world. It has been

reported from countries in North

and South America, Europe,

Africa, Asia, Australia and New

Zealand. EVA outbreaks don’t

occur often, but when they do,

they are frequently associated with

the movement of horses or shipment of semen. 

Widespread dissemination of

the virus can occur 

on breeding farms and at racetracks, sales or horse shows,

where horses are closely congregated. There is growing evidence

that the global distribution of EAV

has been, and continues to be,

influenced significantly by the

international movement of stallions that are carriers of the virus

and by the shipment of infective,

fresh-cooled or frozen semen.

The prevalence of EAV

infection differs conINCIDENCE

GEOGRAPHIC DISTRIBUTION OF EQUINE ARTERITIS VIRUS

NORTH AMERICA

EUROPE

AFRICA

SOUTH

AMERICA

With the increase 

in international

trade of horses and

semen for artificial

insemination, the

risk of spreading

equine arteritis virus

from one equine

population to 

another has grown.

11

■ Conjunctivitis that may be

accompanied by tearing down the

face and swelling above or around

the eyes;

■ Skin rash (urticaria), often

localized to the cheeks or sides of

the neck but sometimes generalized over the body;

■ Abortion; and

■ Pneumonia or pneumonia with

enteritis in very young foals.

Many strains of EAV can cause

abortion in pregnant mares, with

abortion rates varying from 10

percent to as high as 70 percent.

Abortion occurs late in the acute

phase or early in the convalescent

phase of the infection and not, as

some would believe, months after

virus exposure has taken place.

Abortion has been observed as a

sequel to either clinical or asymptomatic infection with EAV. It is

often the result when an unprotected or first-time EVA-vaccinated mare that has very recently

been bred with virus-infective

semen is commingled with one or

more pregnant mares.

Stallions acutely affected with

EVA may experience a period of

temporary subfertility that can

last up to 8 weeks. No long-term

adverse effects on fertility have

been reported in recovered stallions or in stallions that remain

persistently infected with the

siderably both between countries

and between particular horse

breeds in the same country.

Various serological surveys carried out in the United States have

shown that infection with EAV can

be endemic in some breeds, such

as Standardbreds, but not in others, such as Thoroughbreds and

Quarter Horses. There is no evidence, however, that different

breeds vary in their inherent susceptibility to infection with EAV. 

ASIA

AUSTRALIA

NEW

ZEALAND
virus. Similarly, there is no scientific evidence that mares infected

with EAV experience any short- or

long-term, virus-related fertility

problems. Horses in training can

experience a period of impaired

performance while acutely infected with the virus, but fortunately

this is brief.

Except for EVA in young

foals—and this occurs very infrequently—the vast majority of

horses affected with the disease

make total clinical recoveries,

with or without symptomatic treatment. Where indicated, treatment

of cases of EVA is symptomatic and

aimed primarily at alleviating the

severity of some of the clinical

signs of the disease (e.g., control

of fever and reduction of dependent edema). Adequate rest during

the recovery period is important,

especially for breeding stallions

and horses in training.

H O W EAV I S S PREAD

While EAV can be spread among

horses in a number of ways, the

most common routes are respiratory (by the acutely infected animal) and venereal (by the acute

or chronically infected stallion).

Large quantities of EAV are

shed into the respiratory tract of

acutely infected horses, and the

12

virus spreads to other animals

through direct contact with

exhaled infective respiratory secretions. This is the principal means

of dissemination of EAV during outbreaks at racetracks, shows, sales,

and veterinary hospitals. It is also

an important means of transmission on breeding farms. In addition, EAV can be spread through

venereal contact with the semen of

an acutely infected stallion or the

reproductive tract secretions of an

acutely infected mare. A teaser

stallion or nurse mare can be a

potential sources of infection for

outbreaks on breeding farms.

The chronically infected or carrier stallion plays a major role in

venereal transmission of the virus

whether mares are bred by “live

cover” or by artificial insemination.

Another danger is venereal spread

of EAV through the use of infective,

fresh-cooled or frozen semen.

Mechanical spread of EAV can

occur, though this route is believed

to be less common. Virus-contaminated tack or equipment shared

among horses can be a source of

the virus for new hosts, and EAV

can also be transported on the

hands or clothing of personnel

handling the animals.

Finally, EAV can be transmitted

across the placenta from an infected pregnant mare to her unborn

foal. In such cases, the fetus, fetal

fluids, placenta, and placental fluids are plentiful sources of virus.

PERSISTENT EAV INFECTION IN THE

STALLION

A variable percentage of stallions

infected with EAV may become

long-term carriers and reservoirs

of the virus. The carrier state has

been identified only in stallions

whose blood is positive for antibodies to the virus. Such animals

show no clinical signs of disease

nor any adverse effects on fertility,

in spite of harboring the virus in

certain of the accessory sex glands.

Duration of virus persistence can

vary greatly in individual stallions,

ranging from a period of several

months to many years. A small

percentage of carrier stallions successfully clear the virus from their

reproductive tract and are no

longer a source of infection. EAV

is shed constantly in the semen of

carrier animals, and transmission

of the virus occurs solely by the

venereal route. Transmission rates

as high as 100 percent can take

place in mares bred by live cover

or artificial insemination.

Currently, there is no proven

nonsurgical means of eliminating

EAV from a carrier stallion’s 

reproductive tract.

The carrier state has never

been confirmed in stallions vaccinated with the current modified

live-virus vaccine against EVA.

Furthermore, mares, geldings, or

sexually immature colts do not

become persistently infected or

carriers of EAV.

E CONOMIC

SIGNIFICANCE OF EVA

EVA can have economic consequences for both breeding and

performance sectors of the horse

industry.

Direct financial losses resulting from outbreaks of the disease

on breeding farms can be summarized as follows: 

■ Losses due to abortion and/or

disease and death in young foals,

■ Decreased commercial value of

stallions that become persistently

infected with the virus,

■ Reduced demand to breed to

carrier stallions because of the

added expense and inconvenience

involved in vaccinating and 

isolating mares before and after

breeding,

■ Denied export markets for carrier stallions or virus-infective

semen, and

■ Reduced export markets for 

fillies, mares, colts, and geldings,

13
14

A 1998 horse industry study by APHIS’ National Animal Health Monitoring

System indicates that very few horses in the United States are vaccinated

against EVA.

8 %

6 %

4 %

2 %

0%

1–5 6–19 20 or more all operations

horses horses horses 

SIZE OF OPERATION (number of resident horses)

Operations that vaccinated at least one horse against EVA

EVA VACCINATION RATES and noncarrier stallions positive

for serum antibodies to the virus.

An outbreak of EVA at a racetrack, equestrian event, or horse

show can have considerable impact

because of the potential for widespread transmission of EAV among

closely congregated horses. Such

occurrences can result in direct

financial losses through disruption

of training schedules, reduced race

or competition entries, and even

the cancellation of races or events.

In summary, outbreaks of EVA

can have considerable economic

consequences for the horse industry. At the national level, the disease can be responsible for financial losses on breeding farms, at

racetracks, equestrian events, or

horse shows. At the international

level, EVA has significantly affected trade in horses and semen with

denied export opportunities for

carrier stallions, EAV-infective

semen and, in some cases, all categories of horses that are positive

for antibodies to the virus.

H O W T O C ONFIRM A

DIAGNOSIS OF EAV

It is not possible to establish a

diagnosis of EVA based solely on

the nature and extent of clinical

signs observed in affected animals.

The clinical signs of EVA are sim15

ply not distinctive enough from

those observed in certain other

infectious and noninfectious diseases of the horse. Diseases that

can clinically mimic EVA include

equine rhinopneumonitis, influenza, purpura hemorrhagica, equine

infectious anemia, urticaria, and

toxicosis due to particular plants

(e.g., hoary allysum). Also, a few

equine diseases exotic to the

United States could be confused

on clinical grounds with EVA. The

most economically important of

these is African horse sickness.

The only definitive means of

establishing a diagnosis of EVA is

by laboratory testing of appropriate specimens, preferably obtained very early in the course of the

infection. In the case of the

acutely infected horse, EAV can 

be detected in certain tissues 

and fluids, such as nasal or conjunctival secretions, blood, semen,

and, with respect to an aborted

fetus, placental and fetal fluids

and tissues. To maximize the

chances of confirming a diagnosis,

it is very important that your veterinarian collect the appropriate

specimens as soon as possible

after the onset of clinical signs

and as early as possible in a suspected outbreak of EVA.

Besides attempting to detect

EAV in a clinically affected ani-
mal, your veterinarian can confirm

a diagnosis of EAV infection by

testing paired blood samples for

the presence of antibodies to the

virus. Have your veterinarian collect the initial blood sample as

early as possible in the course of

the disease and obtain a second

sample 3–4 weeks later. Although

highly reliable, laboratory examination of paired (acute and convalescent) blood samples suffers

from the disadvantage of not providing a rapid diagnosis of EVA.

Screening of a stallion for the

carrier state initially involves having your veterinarian take a blood

sample for laboratory testing to

determine if the animal is positive

or negative for serum antibodies to

EAV. Only stallions testing positive

(neutralizing antibody level or

titer of 1:4 or greater) without any

history of previous vaccination

against EVA should be considered

potential carriers of the virus. All

antibody-positive nonvaccinated

stallions should be screened for

presence of the carrier state by

either (1) attempting detection of

EAV in semen in the laboratory, or

(2) subjecting them to a testbreeding program involving two

seronegative mares and monitoring the mares for the development

of serum antibodies to the virus up

to 28 days after breeding. Virus

16

detection in the laboratory is 

inexpensive and safe and provides

a timely result. It can be attempted at any time before, during, or

after the breeding season because

carrier stallions shed EAV constantly in their semen. It should

be reemphasized that semen collected for virological examination

must contain the sperm-rich fraction of the ejaculate.

Specimens from a suspected

outbreak of EVA or from a stallion

that is a putative carrier of EAV

should be appropriately handled

as advised by your veterinarian

and submitted to a laboratory

known to have the diagnostic

capability and proficiency in testing for this infection.

PREVENTING THE

S PREAD OF EAV

Control Programs

Although not generally realized

by many in the horse industry, EVA

is a very controllable disease.

Controlling its spread involves

minimizing or eliminating 

direct or indirect contact of 

susceptible horses with various

secretions, excretions, or tissues

of infected horses.

Based on the outcome of a

great deal of scientific investigation of the natural and experimentally reproduced disease and the

causal agent, EAV, various industry

groups have developed effective

programs for the prevention and

control of EVA. Integral to 

the success of such programs is

the availability of a safe and 

effective vaccine (ARVAC®, Ft.

Dodge Animal Health) that stimulates a high level of protection

against the disease.

Current control programs are

focused primarily on restricting

spread of the virus in breeding

horse populations to (1) prevent

outbreaks of EAV-related abortion

and/or illness and death in very

young foals and (2) minimize the

risk of establishment of the carrier

state in stallions. Notwithstanding

the potential economic consequences involved, there are no

ongoing programs targeted at preventing the introduction or

restricting the spread of EAV

among performance horses either

at racetracks, equestrian events,

or horse shows.

EVA can be effectively controlled if you observe sound management practices and implement

a selective vaccination program

against the disease. Current programs have centered largely

around the importance of the carrier stallion as a reservoir of EAV

and the means whereby the virus

17

can be widely disseminated in susceptible breeding populations.

The following specific preventive

and control measures can help you

minimize the spread of EVA:

■ Isolate all new arrivals and

horses returning from other farms,

sales, or racetracks for 3 to 4

weeks.

■ If at all possible, segregate pregnant mares from other horses on

the farm and maintain mares in

small groups until they have

foaled.

■ Prior to the start of each breeding season, blood-test all new

breeding stallions for the presence

of antibodies to EAV.

■ Have the semen of any antibodypositive, nonvaccinated stallion

laboratory-tested to identify any

carrier animals.

■ Annually vaccinate all noncarrier breeding stallions at least 4

weeks prior to the start of each

breeding season.

■ Maintain any EAV carrier stallions in physical isolation.

■ Observe strict hygienic precautions when breeding or collecting

from carrier stallions to avoid the

risk of inadvertent transfer of

infection through indirect contact

with virus-contaminated objects.

■ Restrict breeding EAV carrier

stallions to only vaccinated mares

or mares that have previously test-
ed positive for naturally acquired

antibodies to the virus.

■ Vaccinate EAV antibody-negative

mares against EVA at least 3 weeks

prior to breeding to a known carrier stallion or with virus-infective

semen. Mares do not have to be

revaccinated if they require to be

rebred to the same or another carrier stallion.

■ For 3 weeks after they have

been bred to a carrier stallion, isolate mares vaccinated for the first

time against EVA from all but

known EAV antibody-positive animals. It is especially important to

avoid contact between such mares

and other pregnant mares, to

which they can spread the virus by

the respiratory route.

In breeds in which EAV 

infection is endemic (e.g.,

Standardbreds or various

Warmblood breeds), we strongly

recommend that you vaccinate all

colts (immature male foals)

between 6 and 12 months of age

against EVA. This practice will

minimize, if not eliminate, the risk

of their becoming carriers of the

virus at a later date. If rigorously

implemented over a period of

years, such a vaccination strategy

will lead to a very significant

reduction in the number of carrier

stallions and largely eliminate the

primary reservoir of EAV.

18

There is a very real danger 

of introducing EAV into a susceptible horse population through 

the use of infective, fresh-cooled

or frozen semen. In light of the

significant risk involved, it is

important that you take the preliminary step of determining the

virus infectivity status of semen

used for artificial insemination,

especially if it has been imported

from abroad. The precautions you

should take with mares artificially

inseminated with EAV containing

semen are identical to those recommended for mares bred by live

cover to a carrier stallion.

In an effort to promote greater

national control of EVA, and bearing in mind the important role

that the carrier stallion plays in

the dissemination of EAV, the

American Horse Council formed 

a working group in September

1996 to develop guidelines for

breeding a mare to an EVA-shedding stallion. The working group

included representation from the

following breed organizations: the

American Quarter Horse Association, the U.S. Trotting Association,

the Tennessee Walking Horse

Breeders & Exhibitors Association,

the International Arabian Horse

Association, the Appaloosa Horse

Club, the Federation of North

American Sport Horse Registries,

and the Jockey Club. The group

also included Dr. Ralph Knowles,

of the Maryland Department of

Agriculture and chairman of the

United States Animal Health

Association’s Committee on

Infectious Diseases of Horses; 

Dr. Don Lein, director of the

Veterinary Diagnostic Laboratory

at Cornell University; and 

Dr. Don L. Notter, Kentucky 

State Veterinarian.

The overall goal of the 

working group was to develop a

voluntary, industry-driven protocol

to assist breeders in preventing

the spread of EVA. The guidelines,

released in August 1997, were subsequently endorsed by the

American Association of Equine

Practitioners and the United

States Animal Health Association.

They are available at the

American Horse Council’s Website

(www.horsecouncil.org). 

Click on the Equine Health

Advisory button.

Action To Be Taken in the

Event of an Outbreak of EVA

When dealing with a suspected

outbreak of EVA, you should make

every effort to restrict spread of

the virus and minimize potential

economic losses from the disease.

Take the following measures in

the case of an outbreak on a

breeding farm:

19

■ Promptly isolate all affected

horses.

■ Notify your veterinarian immediately.

■ In consultation with your veterinarian, seek laboratory confirmation of a diagnosis as soon as

possible.

■ In the case of abortion or death

in a newborn foal, place the placenta, fetus, or foal in a leak-proof

bag, keep cold (not frozen), and

dispatch to the nearest qualified

diagnostic laboratory.

■ Disinfect stall, any equipment,

or other potentially contaminated

facilities using a phenolic disinfectant. After treatment with disinfectant, dispose of any bedding by

composting in an area away from

other horses.

■ Using the antiseptic recommended by your veterinarian, wash down

the hindquarters and tail of any

mare that has aborted and isolate

her from other horses for 4 weeks.

■ Restrict movement of horses

onto or off the affected premises. 

■ Suspend breeding operations

until the outbreak is over and notify owners of mares on the affected

premises. You can safely breed

mares affected with EVA later in

the same breeding season once

they have fully recovered from the

disease and there is laboratory

confirmation the outbreak is over.
20

■ Vaccinate all at-risk horses.

■ Notify the State Veterinarian or

appropriate regulatory agency of

the outbreak.

Measures to be taken in the

event of an outbreak of EVA at a

racetrack, equestrian event, or

horse show are broadly similar to

those recommended for dealing

with an outbreak on a breeding

farm. Place major emphasis on

isolating affected animals,

restricting movement in and out

of the facility, and vaccinating all

at-risk animals at the earliest

opportunity as advised by your

veterinarians, working in consultation with the State Veterinarian

and other regulatory officials.

IMMUNIZATION

AGAINST EVA

In sharp contrast to the vast

majority of other equine 

infectious diseases, infection with

EAV stimulates a very strong and

durable protective immunity

against EVA. This immunity can

result from natural exposure to

the virus or from vaccination

against the disease.

At the present time, there is

only one commercially available

vaccine against EVA in North

America. ARVAC is a modified

live-virus vaccine containing an

experimentally derived, highly

attenuated strain of EAV that is

safe and very effective when used

in accordance with the manufacturer’s recommendations. Have

your veterinarian administer the

vaccine to stallions at least 4

weeks prior to the start of the

breeding season. Extensive use 

of the vaccine since 1985 has

failed to reveal any evidence that

the vaccine virus is shed in the

semen or that it can establish the

carrier state in the vaccinated

stallion. We do not recommend

that you use the vaccine in pregnant mares or in foals less than 6

weeks of age unless the risk for

natural infection with EAV is high,

and then only on the advice of

your veterinarian.

Horses immunized with the

modified live-virus vaccine against

EVA on two or more occasions

develop high antibody titers to the

virus equivalent to those observed

in cases of naturally acquired

infection. Protection afforded by

vaccination is considered to last

for at least several years.

21

We hope that the information in

this brochure and in the companion video will help promote greater

industry awareness of EVA and dispel much of the misinformation

that has prevailed since the epidemic in Kentucky in 1984. EVA

can be a source of considerable

economic loss, especially for the

horse breeding industry. It is high

time, therefore, that a more rigorous effort be made to achieve

greater control over this infection

at the national level.

The success of any voluntary

prevention and control program

against EVA, however, will be critically dependent on your involvement and support and that of other

members of the horse industry

working in cooperation with veterinarians and Federal and State animal health officials. The organizations and individuals who produced

this brochure and companion video

did so to convince you of the need

to participate in such a program

and reduce the prevalence of what

is a very controllable disease in the

U.S. horse population.

C ONCLUSIONS
Cole, J. R.; Hall, R. F.; Gosser, H. S.,

et al. 1986. Transmissibility and

abortigenic effect of equine viral

arteritis in mares. Journal of the

American Veterinary Medical

Association 189(7): 769–771.

Collins, J. K.; Kari, S.; Ralston, S. L.,

et al. 1987. Equine viral arteritis at

a veterinary teaching hospital.

Preventive Veterinary Medicine 4:

389–397.

Glaser, A. L.; de Vries, A.A.F.;

Rottier, P.J.M., et al. 1996. Equine

arteritis virus: a review of clinical

features and management aspects.

The Veterinary Quarterly 18(3):

95–99.

Golnik, W.; Michalska, Z.; Michalak,

T. 1981. Natural equine viral arteritis in foals. Schweizer Archiv Fur

Tierheilkunde 123: 523–533.

McCollum, W. H. 1970. Vaccination

for equine viral arteritis. In: Equine

infectious diseases II, proceedings

of the 2nd international conference;

16–18 June 1969; Paris, France.

Basel, SW: Karger: 143–151.

22

McCollum, W. H.; Swerczek, T. W.

1978. Studies of an epizootic of

equine viral arteritis in racehorses.

Journal of Equine Medicine and

Surgery 2: 293–299.

McCue, P. M.; Hietala, S. K.;

Spensley, M. S., et al. 1991.

Prevalence of equine viral arteritis

in California horses. California

Veterinarian March–April: 24–26.

Scollay, M. C.; Foreman, J. H. 1993.

An overview of the 1993 equine

viral arteritis outbreak at Arlington

International Racecourse. In: 39th

annual convention, proceedings;

5–8 December 1993; San Antonio,

TX. Lexington, KY: American

Association of Equine Practitioners:

255–256.

Timoney, P. J. 1984. Clinical, virological and epidemiological features of the 1984 outbreak of

equine viral arteritis in the

Thoroughbred population in

Kentucky, USA. In: Proceedings of

the Grayson Foundation international conference of Thoroughbred

breeders organizations on equine

viral arteritis; 31 October –

1 November 1984; Dromoland

Castle, Co. Clare, Ireland.

Lexington, KY: Grayson Jockey Club

Research Foundation: 24–33.

SUGGESTED READINGS

Timoney, P. J. 1999. Equine viral

arteritis in perspective: fact vs. fiction. In: Proceedings of the sixth

World Equine Veterinary Congress;

30 September–3 October 1999;

Paris, France. Reims, FR:

Boehringer Engelheim: 167–170.

Timoney, P. J.; McCollum, W. H.

1993. Equine viral arteritis.

Veterinary Clinics of North America:

295–309.

Timoney, P. J.; McCollum, W. H.;

Murphy, T. W., et al. 1987. The carrier state in equine arteritis virus

infection in the stallion with specific emphasis on the venereal mode

of virus transmission. Journal of

Reproduction and Fertility 35:

95–102.

Timoney, P. J.; McCollum, W. H.;

Roberts, A. W. 1987. Detection of

the carrier state in stallions persistently infected with equine arteritis

virus. In: Proceedings of the annual

meeting of the American Association of Equine Practitioners; 29

November–3 December 1986;

Nashville, TN. Lexington, KY:

American Association of Equine

Practitioners: 57–65.

23

Timoney, P. J.; McCollum, W. H.;

Vickers, M. L. 1998. The rationale

for greater national control of EVA.

Equine Disease Quarterly 7(1):

2–3.

Timoney, P. J.; Umphenour, N. W.;

McCollum, W. H. 1988. Safety evaluation of a commercial modified

live equine arteritis virus vaccine

for use in stallions. In: Powell, 

D. G., ed. Equine infectious diseases V. Proceedings of the 5th

international conference; 7–10

October 1987; Lexington, KY.

Lexington, KY: The University

Press of Kentucky: 19–27.

U.S. Department of Agriculture,

Animal and Plant Health Inspection Service. 2000. Equine viral

arteritis (EVA) and the U.S. 

horse industry. N315.0400. Ft.

Collins, CO: U.S. Department of

Agriculture, Animal and Plant

Health Inspection Service,

Veterinary Services, Centers for

Epidemiology and Animal Health,

National Animal Health Monitoring

System. 34 p.
We wish to thank those 

individuals and groups who 

provided valuable suggestions 

and support during the development of the video “Equine Viral

Arteritis: A Manageable Problem,”

especially: Amy Mann and the

American Horse Council’s EVA

working group; Ralph Knowles 

and the United States Animal

Health Association’s Infectious

Diseases of Horses Committee;

Rusty Ford, manager of equine 

programs at the Kentucky

Department of Agriculture’s

Division of Animal Health; and

USDA’s EVA review committee.

24

Funding to produce the video

and this brochure was provided by

USDA, APHIS, Veterinary Services.

We gratefully acknowledge the support of Primedia Publications, publishers of EQUUS magazine, in supplying the artwork used in the

brochure and on the video case and

in preparing the layout of these

publications. All illustrations are

copyrighted by Primedia

Publications, Gaithersburg, MD,

and may not be reproduced without

their written permission. The

horse images used in some of these

illustrations remain under copyright by the original photographers.

A CKNOWLEDGMENTS