A Disease guide for owners.

Equine Viral Arteritis is a contagious disease of equids (horses, donkeys, zebras and mules) caused by the equine 

arteritis virus.  Although rarely fatal, the disease is of great economic importance for breeding farms and training stables, and has resulted in specific import regulations of horses and semen. 

Clinical Signs:

The majority of horses that become infected with the virus show no signs of  illness!  Horses that are suffering from equine viral arteritis present with general signs of illness including fever (near 40.5 degree celcius) for 1-5 days, anorexia, depression, serous nasal discharge, lacrimation (tearing), coughing, edema of limbs, skin rash and swelling of eyelids. Scrotal swelling can be observed in males.  This disease is rarely fatal--in fact most horses recover from illness and elimate the virus completely.  The problem with EVA is its effects on reproductive activities.  EVA can cause abortions in pregnant mares, and can become a chronic infection in breeding stallions.
scrotal edema    lacrimation  Ocular edema   
Scrotal Edema                   Lacrimation                         Conjunctival edema           
Photos Courtesy of Dr. Peter J. Timoney (in Merck Manual Online )


EAV infection can be transmitted among horses in four different ways:Epidemiology of EVA
  1.  Respiratory: An acutely-infected horse spreads the virus to other in contact horses via respiratory secretions (exposure commonly occurs at racetracks, shows, sales and other events).
  2. Venereal: Virus shed in the semen of an infected stallion is transmitted to mares when they are bred.
  3. Indirect contamination: The virus is transferred indirectly through the use of contaminated tack or equipment shared among horses or on hands or clothing of personnel handling animals.
  4.  In utero: Virus passes across the placenta from an  infected mare to her unborn foal.

What your vet will do if they suspect your horse is infected with EVA:

  • Since the signs of equine viral arteritis are fairly general, your vet will send off samples to a diagnostic lab to confirm that your horse has been infected with the equine arteritis virus.  Lab results are the only means of confirming a diagnosis of EVA  as there are other pathogenic organisms that cause similiar disease. 
  • Provide supportive care if it is a severe case. Your vet will work to make your horse as comfortable as possible--giving it anti-inflammatories, anti-pyretics, and diuretics to help control the pain, fever, and swelling if they think it is necessary to do so.
  • EVA is caused by a virus--this means that there are no antibiotics to be given!  Most horses have a full and uncomplicated recovery from this infection.  Click the link to discover the implications this disease has for your MARE or STALLION

Control of EVA:

Horses naturally infected with EAV develop strong long-lasting immunity against it.  Immunity can also be induced by vaccination.  Click the appropriate link for information on vaccinating your breeding MARE, STALLION, or NON-BREEDING horse. 

What is the big deal about EVA? 

Even though EVA is not usually a life threatening disease, or even frequently encountered in Western Canada, it is important for horse owners to know about, especially if they intend to breed their horses or take them across the border.  On breeding farms it is of significant importance because of the reproductive losses due to abortion, and the costs of implementing quarantine and control measures.  At the race track or training stable, a loss of opportunity for training or racing while the horses are sick or convalescing is an important ramification of the disease.  Import regulations are also in place that govern the movement of horses--these regulations require proof that a horse has not been exposed to virulent EVA. 


  • The Merck Veterinary Manual.  Equine Viral Arteritis Introduction.  www.merckvetmanual.com 
  • AAEP Guidelines for the Vaccination of the Horse.  http://www.xcodesign.com/aaep/displayArticles.cfm?ID=171
  • Del Piero, F.  Equine Viral Arteritis.  Vet Pathol 37:287-296 (2000).