Equine Viral Arteritis Flashcards
Equine viral arteritis (EVA)
a contagious disease of equids so named because of its characteristic vascular pathology
What is the causal agent of EVA?
equine arteritis virus (EAV)
When was EVA first defined?
1953 - following an outbreak of respiratory disease and abortion in Ohio
What happened in 1984 with EVA?
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
Principal industry concerns with EVA
-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
What are some reasons why there has been in increase in reported outbreaks of EVA?
-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
How did EVA spread in acutely infected horses?
-respiratory
-venereal
-congenital (pregnant mare)
-indirectly through contaminated fomites
How did EVA spread in chronically infected stallions?
-venereal
-solely by direct sexual contact
-indirectly through virus contaminated fomites
How long is EVA incubation period?
2-13 days
After the incubation period, when does respiratory tract secretions shed the virus?
2-16 days
After the incubation period, when does urine shed the virus?
1-28 days
After the incubation period, when does semen shed the virus?
7 days to years
After the incubation period, when does the reproductive tract secretions (mare) shed the virus?
2-9 days
How long can the virus be detected in the buffy coat cells of the blood?
1-21 days
Where does the spread of EVA usually occur?
-racetrack
-breeding farm
-veterinary hospital
-show/sales
What is the primary spread of EVA at breeding farms?
venereal transmission
-carrier stallion
-natural service
-AI
-embryo transfer
What are the top two means of spread of EVA?
-importation of carrier stallions
-importation of virus-infective semen
Clinical outcome of natural infection with EVA:
-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
Clinical signs of EVA:
-fever
-inappetence
-depression
-leukopenia
-dependent oedema (limbs, scrotum, prepuce, mammary glands)
-conjunctivitis
-skin rash
Mortality rate:
-infrequent in foals a few days to a few months old
-very rare in older horses
Clinical signs in breeding horses:
-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
The carrier state
-frequent occurence as a sequel to natural infection in the stallion
-unconfirmed in the mare, gelding, or sexually immature colt
Establishment and maintenance of the carrier is dependent on what?
testosterone
Characteristics of stallions persistently infected with EAV
-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)
What is the transmission rate of the carrier stallion?
85-100% in susceptible mares bred naturally or by AI
Sources of economic loss resulting from EVA
-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
How is EVA diagnosed?
-laboratory tests
-virus detection and/or demonstration of antibodies to the virus in paired sera
What other diseases resemble EVA?
-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
Treatment of EVA
-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
Prevention of EVA:
-minimize risk of virus related abortion
-prevent establishment of the carrier state in the stallion
-modified live vaccine
How long can vaccinal induced immunity last for?
1+ years
How long can maternally acquired passive protection (from vaccines) in foals last?
2.5-6 months
Can vaccinated stallions and their semen be exported to other major horse breeding countries?
yes
Measures to control EVA:
-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
When should colt foals be vaccinated?
between 6 and 12 months old
