EVA Flashcards
What is the etiological of EVA (Equine viral arteritis)?
Equine arteritis virus which is single stranded enveloped RNA virus of the same family than porcine respiratory and reproductive virus syndrome.
What breed of horse EVA is more prevalent?
EVA is more commonly diagnosed in Standardbreds, but lately high number of cases on Warmbloods have been diagnosed.
What is the most common route of transmission for EVA?
The most common route of transmission is through contamination with respiratory secretion of acutely infected horses. The disease can also be transmitted venereally by Stallion persistent infected with the virus and there is also transplacental transmissions from infected mare to unborn foal. There has been also report of contamination during embryo transfer due to semen contaminated with the virus and by a variety of fomites contaminated with the semen of persistently infected Stallions and infectious secretions of an infected horses, and through contact with aborted fetus, fetal membranes, and fetal secretions.
What are the clinical signs associated with EVA?
The majority of primary cases are asymptomatic. The clinical signs associated with EVA depend on the virus, host immunity, and environment.
The signs appear 2-13 after infection (generally 6-8 days after venereal infection) and vary from:
- Fever
- Anorexia
- Leukopenia
- Depression
- Supraorbital and periorbital edema
- Nasal discharge and ocular discharge
- Conjunctivitis
- Photofobia
- Skin rash maybe localized to face, neck or pectoral region or generalized to the body
- Dependent edema especially of the lower limbs, scrotum and prepuce in the males, and mammary glands in the female
A range of other clinical signs include coughing, respiratory distress, submaxilar lymphadenopathy, posterior paresis or ataxia, swelling of submandibular area, pectoral and shoulder, gingival and bucal erosions, and infrequently diarrhea.
The duration of the clinical signs is generally 2 weeks.
Young, old, and debilitated horses have more severe cases of EVA.
With few exceptions horses with clinical signs of EVA has uneventful recoveries.
Abortion can range from less than 10% to greater than 70% for unprotected mares and can be sequential to asymptomatic or clinical cases.
Cases of abortion can occur between 3 and 10 months of gestation.
Infection very late in gestation might result in the birth of infected foals and the placental fluids and tissues are very infective with EVA to any unprotected animals.
It seems that abortion only occurs when a pregnant mare is contaminated via the respiratory route and not venereal route. Thus, mare bred with semen contaminated with EVA that had conception will not abort because EVA that is in the semen can be harbor in the mare and contaminated the fetus later.
Stallions contaminated with EVA that develop several clinical signs including edema of prepuce and scrotum may become febrile and have an transient period of infertility unless treated promptly. Changes will include decrease percentage of normal sperm that commences 1 week after infection and reach a nadir at ~week 7 before returning to normal levels in 16 weeks.
What is pathogenesis of EVA?
The virus invades the respiratory epithelium and rapidly replicates in bronchial and alveolar macrophages before migrating to lymph nodes. Within 3 days a leukocyte mediated viremia develops and the virus goes to all tissues and fluids in the body. By 6 to 8 days a generalized vasculitis characteristics of virus occurs leading to most of clinical signs present in the disease. Maximal vascular injury is noticed at 10 days into the infection, after which the lesions start to resolve. The pathogenesis for abortion remain to be elusive. Pathological evidence suggest that fetal death occur prior to parturition. EVA-related abortion are frequently associated with minimal vascular to other tissue damage of the placenta and fetus.
What percentage of Stallions become carriers for EVA?
Frequency of the carrier state can vary from less than 10% to more than 70%. Viral persistence of the Stallion might be several weeks, months, or many years. NOT all Stallions will remain carriers for life. Many will clear the infection. Establishment and carrier maintenance is androgen-dependent with EVA harbored in certain accessory sex glands, especially the ampulla and vas deferens. Virus are present in sperm rich fraction. Success of transmission either from natural service or insemination can be as high 85-100%. Carrier stallion are soropositivo for antibodies for EAV, are clinically normal, and have normal fertility.
How can EVA be diagnosed?
Clinical signs are only suggestive of the disease. In animals where acute infection and clinical signs are present, virus isolation, RT-PCR, or demonstration of specific antibodies for virus can be used as diagnostic tools.
Appropriate specimens to collect are nasal swabs or washes, and blood samples on citrate or EDTA or clotted blood. Specimens should be collected as soon as possible after fever or other clear clinical signs.
In cases of abortion, virus isolation from fetal lungs, liver can be used to diagnosis the virus. Specimens should also be taken for IHC.
For identification of carrier Stallion history needs to be considered. Only Stallion with antibody titter > 1.4 and without history of vaccination should be considered potential carrier. The carrier state is confirmed by demonstration of virus in the sperm-rich fraction of the semen by virus isolation or RT-PCR.
What is the treatment of EVA?
Limited to controlling the severity of clinical signs. Temporary down regulation of testosterone GnRH antagonist and GnRH immunization has been associated with elimination of EAV in some, but not all Stallions. Recent studies have shown that gradient centrifugation and swim-up protocol for processing semen reduced the presence of the virus in the semen.
How can EVA be prevented?
Two vaccines are commercially available. A modified live virus (MLV) vaccine (Arvac, Fort Dodge Animal Health) approved to be used in US and Canada; and an inactivated vaccine (Artevac, Fort Dodge Animal Health), which is conditionally licensed to be used in Europe. The MLV is safe for Stallion, non-pregnant mares, fillies, and colts. It is not recommended for pregnant mares especially in the last two months of pregnancy. Biosecurity measures that need to be use concurrently with vaccination are minimize or eliminate direct and indirect contact with EAV-naive horses with the secretions of infected animals. Quartantine and isolated incoming horse. Screen Stallions for the condition of carrier and isolate and take proper sanitary measures to contain the carrier infection. Carrier Stallion should preferably only breed naturally seropositive mares or vaccinated mares. Screen all shipped semen. Mares bred with infected semen should be managed naturally seropositive for the virus or vaccinated. In case of an outbreak contact proper regulatory authorities and suspend all breeding activities. All areas should be desinfectes and suspected animals isolated and identified.
