Equine Viral Arteritis

Question 1

Equine viral arteritis (EVA)

Answer 1

a contagious disease of equids so named because of its characteristic vascular pathology

Question 2

What is the causal agent of EVA?

Answer 2

equine arteritis virus (EAV)

Question 3

When was EVA first defined?

Answer 3

1953 - following an outbreak of respiratory disease and abortion in Ohio

Question 4

What happened in 1984 with EVA?

Answer 4

a “watershed year” with respect to perceived importance of EVA, following widespread occurence on TB breeding farms in KY
-marked a change in how equine and regulatory authority viewed potential economic significance of diseases

Question 5

Principal industry concerns with EVA

Answer 5

-risk of spread of disease through national/international movement of horses and semen
-potential cause of abortion outbreaks in naive populations of pregnant mares
-risk of illness and death in foals
-likelihood of establishing the carrier state in a variable % of stallions

Question 6

What are some reasons why there has been in increase in reported outbreaks of EVA?

Answer 6

-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/semen/embryos

Question 7

How did EVA spread in acutely infected horses?

Answer 7

-respiratory
-venereal
-congenital (pregnant mare)
-indirectly through contaminated fomites

Question 8

How did EVA spread in chronically infected stallions?

Answer 8

-venereal
-solely by direct sexual contact
-indirectly through virus contaminated fomites

Question 9

How long is EVA incubation period?

Answer 9

2-13 days

Question 10

After the incubation period, when does respiratory tract secretions shed the virus?

Answer 10

2-16 days

Question 11

After the incubation period, when does urine shed the virus?

Answer 11

1-28 days

Question 12

After the incubation period, when does semen shed the virus?

Answer 12

7 days to years

Question 13

After the incubation period, when does the reproductive tract secretions (mare) shed the virus?

Answer 13

2-9 days

Question 14

How long can the virus be detected in the buffy coat cells of the blood?

Answer 14

1-21 days

Question 15

Where does the spread of EVA usually occur?

Answer 15

-racetrack
-breeding farm
-veterinary hospital
-show/sales

Question 16

What is the primary spread of EVA at breeding farms?

Answer 16

venereal transmission
-carrier stallion
-natural service
-AI
-embryo transfer

Question 17

What are the top two means of spread of EVA?

Answer 17

-importation of carrier stallions
-importation of virus-infective semen

Question 18

Clinical outcome of natural infection with EVA:

Answer 18

-subclinical infection in most cases
-sporadic occurence of clinical disease
-possibility of abortion in pregnant mares
-very rarely, fatal respiratory or pneumo-enteric syndrome in young foals

Question 19

Clinical signs of EVA:

Answer 19

-fever
-inappetence
-depression
-leukopenia
-dependent oedema (limbs, scrotum, prepuce, mammary glands)
-conjunctivitis
-skin rash

Question 20

Mortality rate:

Answer 20

-infrequent in foals a few days to a few months old
-very rare in older horses

Question 21

Clinical signs in breeding horses:

Answer 21

-abortion
-fulminant pneumonia/pneumo-enteritis in neonatal foals and foals up to 3 months of age
-temporary subfertility in stallions
-establishment of the carrier state in the stallion

Question 22

The carrier state

Answer 22

-frequent occurence as a sequel to natural infection in the stallion
-unconfirmed in the mare, gelding, or sexually immature colt

Question 23

Establishment and maintenance of the carrier is dependent on what?

Answer 23

testosterone

Question 24

Characteristics of stallions persistently infected with EAV

Answer 24

-clinically normal
-seropositive 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 25

What is the transmission rate of the carrier stallion?

Answer 25

85-100% in susceptible mares bred naturally or by AI

Question 26

Sources of economic loss resulting from EVA

Answer 26

-abortion and death of foals
-denied export markets for carrier stallions
-disruption of training schedules, reduced race entries and card cancellations
-decreased marketability of carrier stallions

Question 27

How is EVA diagnosed?

Answer 27

-laboratory tests
-virus detection and/or demonstration of antibodies to the virus in paired sera

Question 28

What other diseases resemble EVA?

Answer 28

-EHV 1 and 4
-Equine influenza
-Equine infectious anemia
-purpura hemorrhagica
-urticaria
-toxicosis due to hoary alyssum
-getah virus infection
-african horse sickness fever
-dourine
-equine encephalosis

Question 29

Treatment of EVA

Answer 29

-no specific antiviral treatment available
-symptomatic treatment only
-non-surgical strategies to promote elimination of the carrier state in stallions hasn’t been fully validated

Question 30

Prevention of EVA:

Answer 30

-minimize risk of virus related abortion
-prevent establishment of the carrier state in the stallion
-modified live vaccine

Question 31

How long can vaccinal induced immunity last for?

Answer 31

1+ years

Question 32

How long can maternally acquired passive protection (from vaccines) in foals last?

Answer 32

2.5-6 months

Question 33

Can vaccinated stallions and their semen be exported to other major horse breeding countries?

Answer 33

yes

Question 34

Measures to control EVA:

Answer 34

-identify carrier stallions in a breeding population
-separately manage any carrier stallions
-vaccinate non-carrier breeding stallions annually
-restrict breeding of carrier stallions to EVA vaccinated mares
-screen semen for AI use for virus
-sound management practices for pregnant mares

Question 35

When should colt foals be vaccinated?

Answer 35

between 6 and 12 months old