Equine Viral Arteritis (EVA) Flashcards
EVA definition
a contagious disease
of equids so named because of its characteristic vascular pathology.
►Causal agent is equine arteritis virus (EAV).
principal industry concerns
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.
distribution and prevalence of EVA
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.
why are there more reported EVA outbreaks today?
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.
Acutely infected modes of transmission
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
chronically infected modes of transmission
venereal, solely
by direct sexual contact or indirectly, through virus contaminated fomites.
shedding patterns of EVA by acutely infected horses
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.
EVA means of spread
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.
clinical outcome of natural infection
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.
frequently encountered clinical signs
Fever, inappetence, depression. ► Leukopenia. ► Dependent oedema (limbs, scrotum, prepuce,
mammary glands).
► Conjunctivitis. ► Skin rash.
clinical outcomes of EVA
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.
potential consequences of EVA in breeding populations
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.
the carrier state
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.

significance of the carrier stallion
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.

characteristics of stallions with persistent EVA
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.
EVA transmission by the carrier stallion
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.
diagnosis of EVA
Confirmation of a diagnosis of EVA is based on virus detection and / or demonstration of antibodies to the virus in paired sera.
viruses clinically resembling EVA
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).
EVA treatment
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.
EVA vaccines
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.
vaccine considerations
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.
Control of EVA
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.
