What are Viral Arteritis?
Equine viral arteritis is basically a disease that is very contagious among horses which is not really life-threatening for the average adult horse who is otherwise healthy, but can be fatal to young foals (not a common problem) and, more commonly, can cause pregnant mares to abort. This also can create a situation in which a stallion or a mare could become a carrier of the virus, thus enabling the virus to spread to other mares and stallions through the breeding process as well as via the respiratory system.
The simplest definition for equine viral arteritis is that it is a disease which is caused by an RNA virus that can be found in many countries among horse communities. An RNA virus is one that has RNA (ribonucleic acid) as the genetic material. These viruses do not reproduce using DNA.
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Symptoms of Viral Arteritis in Horses
While a large number of horses who become infected with this virus remain asymptomatic, meaning that they do not show symptoms, when symptoms do surface, it is usually in the acute stage of the viral development. Here are some of the symptoms you might see in your horse, both male and female:
- For mares, abortion can occur and these occurrences can range from 10% to 70% of the EVA-affected mares anytime after 10 to 12 weeks of gestation
- Any or all of flu-like symptoms such as fever, nasal discharge, loss of appetite, respiratory problems, skin rashes, muscle soreness or discomfort, conjunctivitis, or depression
- In some horses who have been infected with EVA, you might also see swelling around the eyes, discharge coming from the eyes, swelling in the limbs, swelling in the genitals of the stallion or swelling in the mammary glands of a mare
While there is really only one type of equine viral arteritis, it can present in the form of a respiratory infection, replete with all of the normal respiratory signs such as fever, nasal discharge, ocular discharge, lack of appetite, and muscle aches, or, it can present in the female and can cause the pregnant mare to abort anytime after about 10 to 12 weeks of pregnancy. It rarely causes death to an adult horse, but it can complicate life expectancies for very young foals (which is less common) or even the ability of the mare to carry the foal to full term, with abortion usually occurring in the final 2 months of gestation. The adult horses, whether male or female may not show any of the above noted symptoms until the virus reaches the acute stage, usually occurring within thirty days of infection.
Causes of Viral Arteritis in Horses
Equine viral arteritis (EVA) is caused by the equine arteritis virus (EAV).
- This virus can live only a short time outside the confines of the body
- However, it is important to note that it can maintain its ability to infect for extended periods of time when protected by bodily fluids and body tissues and when stored near or below freezing temperatures
- The virus can actually stay pretty viable for infection purposes when it is contained in semen that has been frozen for many years
The virus gets into the respiratory system through breathing air in shared or common areas like, but not limited to, stables, pastures, and race tracks. It can also get into a horse’s system during the breeding process, whether using fresh, cooled or frozen semen.
Diagnosis of Viral Arteritis in Horses
Diagnosing this virus is a bit on the challenging side as the symptoms, when they are present, and the clinical signs are very similar to a variety of other viral and bacterial respiratory infections, for example, fever, loss of appetite, muscle aches, and nasal discharge. Many of the infected horses, both male and female, do not generally present with symptoms until the virus is in its acute stage - usually occurring within thirty days of exposure and infection with the possibility of abortion of the fetus in the pregnant mare starting after ten to twelve weeks of conception, occurring most often in the last two months of the gestation period. There are no specific lesions noted in aborted fetuses that will show characteristics of this virus. The most accurate method of diagnosis is by gathering and analyzing samples of blood, semen, nasal discharge, tears or ocular discharge, throat cultures, placenta and fetal samples. These samples will allow the lab to isolate the virus for the veterinarian for purposes of development of a treatment plan.
Part of the analysis of the samples will involve looking at the EVA antibodies present in the sample. Just having some EVA antibodies in the sample doesn’t necessarily mean that the horse is actively infected. For those horses having a large number of antibodies when tested, it is usually necessary to test them again in 14 to 28 days. If the antibodies remain high when these two testings are compared, the animal is considered to have an active infection.
Treatment of Viral Arteritis in Horses
Since there is a virus at the root of this condition, there is no treatment. Antibiotics will not treat the viral root problem. However, in some cases, your vet may choose to treat with antibiotics to reduce the opportunity for a bacterial infection to develop in some horses. As a rule, adult horses will generally recover completely from the effects of the virus but may harbor the virus in the accessory glands of the stallion. This will then result in him becoming a carrier for many years as the virus will live extended periods of time under these conditions. The stallion will essentially become a major source of infection potential for a long time to come.
Recovery of Viral Arteritis in Horses
As noted above, recovery for the average healthy adult horse is generally complete. The virus can remain in various types of tissue in either the male or female horse for many years to come and will become a significant breeding threat for the passing along of the virus. Vaccinations are available to be utilized to protect your negative-tested horses, male and female, against infection by positive-tested horses in their environment. Testing should always be done on both the male and female horse before breeding is attempted, and if one tests positive, always be sure to have the other vaccinated before the breeding is done.
Your veterinarian will provide you with appropriate testing and vaccinating guidelines. In the event that you have a positive-tested horse in your herd, it is imperative to vaccinate it and all the other horses with whom it comes into contact, whether those horses are in your herd or at the race track or involved in any moving process. This disease is very contagious and, since one of the more serious complications from it is involuntary abortion, it is in your best interest, both financially as well as emotionally, to be aware and proactive in the discovery and containment of equine viral arteritis in your herd.