Harrisburg, South Dakota
Excellence in Large Animal Medicine and Surgery since 1981!
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Harrisburg, South Dakota Excellence in Large Animal Medicine and Surgery since 1981! |
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Equine Viral Arteritis – Revisited A viral infection uncovered in a very popular quarter horse stallion this past breeding season has brought to light a contagious disease and all its problems. In this case it involves abortion, quarantine, and vaccination. Equine Viral Arteritis (EVA) is a world wide disease of horses which often lives under the radar until the infection causes problems and is diagnosed. Outbreaks of EVA are infrequent but of special concern because the virus can cause abortion in pregnant mares, death of young foals, and establish a carrier state in stallions. Typical of a lot of viral infections EVA can be spread via respiratory secretions. This virus is also spread in the semen of infected stallions. It can be transmitted by live covering, or artificial insemination with cooled and frozen semen. The infection in this particular stallion was discovered on a breeding farm when a large number of mares came up open on follow up pregnancy exams. By this time not only was it a farm problem but all the mares that were brought in to be bred along with all the semen that had been shipped around the country made it a huge problem. The subsequently infected mare then can shed the virus via nasal droplet spray to other horses they come in contact with. The virus then infects all horses that the newly infected horse contacts and continues to spread. Pregnant mares that get exposed are at risk to abort. Their exposure can be venereal or respiratory. Clinical signs of EVA are usually asymptomatic, meaning nothing is apparent. When symptoms do occur they include a fever, swelling to the legs, respiratory distress, coughing, and edema around the eyes, off feed, abortion, and stillborns. Normal foals can succumb to severe respiratory problems shortly after birth. To diagnose the disease we take blood samples from your horse to detect antibodies against the EVA virus. It may take 2 blood samples collected 2 to 3 weeks apart. Other tests involve sending various samples to the laboratory to detect the virus directly. Mares, geldings, and sexually immature stallions will not become persistent carriers of the disease. Their immune system will build antibodies which will clear the virus. Stallions however can become carriers for an extended period of time, because EVA is a testosterone dependent virus. It is estimated that 30 to 60 % of stallions will become carriers, and continue to shed the virus through their semen. Some stallions will eventually clear the virus and cease to be carriers. Other stallions will shed the rest of their life. The carrier stallions are the EVA virus’s main way to perpetuate in nature. The biggest lessons to be learned involve those in the breeding business. Stallion owners should know the status of their stallions by testing them annually. Vaccination 28 days before the breeding season is an option that should be discussed with your veterinarian. If the stallion is tested positive for antibodies in blood against EVA his semen should be tested to see if he is shedding. Testing to see if the stallion is shedding involves either test breeding to negative mares or evaluating semen for the presence of the virus. The semen is collected and sent to Dr. Timoney’s lab in Kentucky. If the stallion is shedding the virus, the mares that he books need to be vaccinated for EVA 28 days before breeding. This includes natural cover, AI, shipped cooled and frozen semen. If it is determined that he is not shedding the mares would not have to be vaccinated. Stallions which test negative on the blood test and stallions which test positive but are non-shedders can be used normally to breed mares. It is still a good idea to vaccinate negative antibody stallions and non-shedding positive antibody stallions annually 28 days before the start of the breeding season. This is the best assurance that they do not end up becoming carriers by getting exposed to the virus. As mare owners it is important to know the EVA status of the stallion which you are considering to breed your mare. If he is negative or if he is vaccinated and was negative before vaccination there should be no problems. It still may be a good idea to vaccinate your mare anyway to protect against a new outbreak of EVA. If the stallion is positive and shedding you can still breed to him but need to vaccinate your mare 28 days before covering her. You will need to isolate her from all non-positive titer horses for 3 weeks after being covered. Isolation is only necessary the first cycle the mare is bred after vaccination. If revaccinated annually you will not need to post breed isolate again. Before the initial vaccination it is important to test your horse for exposure to the EVA virus and know the current status. After vaccinating the blood test will show positive, and the antibodies will be present to stop infection if the horse is exposed. Once vaccinated testing in subsequent years is not necessary. The vaccine needs to be boostered yearly. Hopefully this outbreak has run its course. We will not know until after the 2007 breeding season and no new outbreaks occurred. Remember that these infections are often non-clinical. We may have a lot of carrier stallions that we do not know about. It makes good sense to vaccinate our mares and is almost critical that we vaccinate our stallions or take other steps to protect them so they do not become carriers and shed the virus. An ounce of prevention is worth a pound of cure. Take proper precautions for a problem free and successful 2007 breeding season. |
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