Equine Viral Arteritis (EVA)

Question 1

EVA definition

Answer 1

a contagious disease
of equids so named because of its characteristic vascular pathology.
►Causal agent is equine arteritis virus (EAV).

Question 2

principal industry concerns

Answer 2

Risk of spread of the disease through national /
international movement of horses and shipment of semen.
►Potential to cause extensive outbreaks of
abortion in naive populations of pregnant mares.
►Risk of illness and death in foals up to a few
months of age.
►Likelihood of establishment of the carrier state
in a variable percentage of stallions.

Question 3

distribution and prevalence of EVA

Answer 3

Virus present in horse populations in
many countries.
►Prevalence of infection can vary widely
among various breeds in the same country and between different countries
Confirmed outbreaks of the disease not
reflective of widespread distribution of
etiologic agent.
►Majority of confirmed cases of infection
continue to be asymptomatic.
►Virus infrequently diagnosed as a cause
of abortion or illness/death in young foals.
►Occurrences at racetracks, horse shows
or sales very sporadic.

Question 4

why are there more reported EVA outbreaks today?

Answer 4

Greater awareness and reporting of disease. ►Bona fide increased incidence of EVA. ►Improved laboratory capability in diagnosing
disease.
►Increased frequency of national / international
movement of carrier stallions / shipment of infective semen / equine embryos.

Question 5

Acutely infected modes of transmission

Answer 5

respiratory, venereal,
congenital (pregnant mare), and indirectly, through virus contaminated fomites.
• Respiratory spread very important in outbreaks on breeding farms, equestrian events, veterinary clinics, sales, etc., and wherever horses come into close contact

Question 6

chronically infected modes of transmission

Answer 6

venereal, solely

by direct sexual contact or indirectly, through virus contaminated fomites.

Question 7

shedding patterns of EVA by acutely infected horses

Answer 7

After an incubation period of from 2 - 13 days following natural exposure to EAV, detectable virus shedding takes place in the following secretions / excretions:
Respiratory tract secretions: 2 - 16 days Urine: 1 - 28 days Semen: 7 days - years Reproductive tract secretions (mare): 2 - 9 days
Virus can also be detected in the buffy coat cells of the blood for 1 - 21 days.

Question 8

EVA means of spread

Answer 8

Movement of horses incubating the infection or
subacutely infected with the virus.
►Importation of carrier stallions - highly important. ►Shipment of virus-infective semen - highly
important.
►Low risk through embryos from an EAV infected
donor mare inseminated with virus infective semen.

Question 9

clinical outcome of natural infection

Answer 9

Subclinical or inapparent infection in the vast
majority of cases.
►Sporadic occurrence of clinical disease of
varying severity.
►Possibility of abortion in pregnant mares.
►Very infrequently, fatal respiratory or pneumo-
enteric syndrome in young foals.

Question 10

frequently encountered clinical signs

Answer 10

Fever, inappetence, depression. ► Leukopenia. ► Dependent oedema (limbs, scrotum, prepuce,
mammary glands).
► Conjunctivitis. ► Skin rash.

Question 11

clinical outcomes of EVA

Answer 11

Regardless of severity of clinical signs, natural cases invariably make complete clinical recoveries.
► Mortality in naturally acquired infection is an infrequent occurrence in foals a few days to several months of age, and a very rare outcome in older horses.

Question 12

potential consequences of EVA in breeding populations

Answer 12

Abortion.
► Fulminant pneumonia / pneumo-enteritis in congenitally infected neonatal foals and in foals up to 3 months of age.
► Temporary subfertility in stallions.
► Establishment of the carrier state in the stallion.

Question 13

the carrier state

Answer 13

Frequent occurrence as a sequel to natural infection in the stallion.
► Unconfirmed in the mare, gelding or sexually immature colt.
► Establishment and maintenance of the carrier state is testosterone-dependent.


Question 14

significance of the carrier stallion

Answer 14

Principal reservoir of the virus between outbreaks of the disease.
► Very important role in equine arteritis virus transmission on breeding farms.
► Source of genetic and phenotypic diversity among strains of the virus.


Question 15

characteristics of stallions with persistent EVA

Answer 15

Clinically normal.
► Seropositive (SN titre ≥ 1:4) for antibodies to the virus.
► Constant semen shedders of the virus.
► Predilection sites of virus persistence - certain of the accessory sex glands, especially the ampulla of the vas deferens.

Question 16

EVA transmission by the carrier stallion

Answer 16

Infection spread solely by the venereal route.
► No evidence of spread by the respiratory or
other non-venereal routes.
► Transmission rates of 85 - 100% in susceptible mares bred naturally or by A.I. with virus infective semen.

Question 17

diagnosis of EVA

Answer 17

Confirmation of a diagnosis of EVA is based on virus detection and / or demonstration of antibodies to the virus in paired sera.

Question 18

viruses clinically resembling EVA

Answer 18

Equine herpesvirus 1 or 4 infections.
► Equine influenza.
► Equine infectious anemia.
► Purpura hemorrhagica.
► Urticaria.
► Toxicosis due to hoary alyssum (Berteroa
incana).
► Getah virus infection (exotic).
► African horse sickness fever (exotic).
► Dourine (exotic).
► Equine encephalosis (exotic).

Question 19

EVA treatment

Answer 19

Symptomatic treatment only indicated in moderate to severe clinical cases of the disease, especially important in affected stallions.
► Non-surgical strategies to promote elimination of the carrier state in the stallion have yet to be fully validated.

Question 20

EVA vaccines

Answer 20

Used in the USA and Canada since 1985, and more recently, New Zealand.
► Safe and highly effective for use in stallions and non-pregnant mares.
► Does not persist in the reproductive tract of the stallion. Inactivated vaccine (ARTERVAC®, Ft. Dodge Animal Health):
► Licensed for use in France, Germany, Ireland, and the United Kingdom.
► Safe and reputedly effective for use in stallions and mares.

Question 21

vaccine considerations

Answer 21

Stimulates effective protection against clinical disease and establishment of the carrier state in the stallion.
► Vaccinal induced immunity can last for 1+ years.
► Maternally acquired passive protection in foals
can persist for 2.5 – 6 mo.
► Vaccinated stallions and their semen can be exported to other major horse breeding countries.

Question 22

Control of EVA

Answer 22

Identify carrier stallions in a breeding population.
► Separately manage any carrier stallions.
► Vaccinate non-carrier breeding stallions annually.
► Restrict the breeding of carrier stallions to EVA vaccinated mares or mares naturally seropositive to EAV.
► Isolate mares bred for the first time to a shedding stallion from EAV seronegative horses for 3 weeks.
► Screen semen for A.I. use for virus; if EAV positive, observe same precautions as recommended for
natural service.
Observe sound management practices especially for pregnant mares.
► Vaccinate colt foals between 6 & 12 months of age to avoid possible development of carrier state later.
► Under circumstances of intensive management of mares (feed-lot situation), highly advisable to vaccinate all at-risk animals.
► In situations of frequent animal movement onto a premises & limited facilities to isolate incoming horses, highly advisable to vaccinate all at risk equines.