Breeding has become a more and more international business with the possibility of artificial insemination and acquiring semen from all over the world. Next to giving us more possibilities when it comes to breeding horses it also has increased the risk of spreading a virus causing Equine Viral Arteritis.
Equine Viral Arteritis or EVA, is a highly contagious viral disease and can cause a variety of clinical signs, varying in severity. Infection with EVA can be obvious and the horses would show fever, cough, nasal discharge, inflammation around the eyes, swelling of the lower limbs, birth of weak or sick foals, and abortion. But an obvious detectable illness might not always be present.
There are multiple ways in which EVA can be transmitted between horses. When a horse has been infected it can transfer the virus via droplets coughed or snorted out. When a mare has aborted the fetus and the placenta, when touched, can transfer the virus. The main worry and transmission route is via semen, either through natural cover or artificial insemination because the virus can survive in chilled and frozen semen.
A concern surrounding EVA is that, even if horses show no sign of illness at all, they can still be able to transmit the virus to other horses. This is problematic because this poses a difficulty if the horse is not clinically ill, they will be hard to detect and to stop from infecting other horses. This is mostly a problem with stallions. They can excrete the virus in their semen, their fertility is not affected, and spread the virus via artificial insemination and natural cover. These stallions are called ‘shedders’. This happens to about 30% of the infected stallions. These stallions can spread the virus for weeks, months or even years – possibly even for life.
These stallions pose a significant risk of transmission of the disease. The mares that get inseminated could abort their pregnancy, give birth to a weak or dead foal or get clinical signs from the virus and these mares may, in turn, infect other horses. In the UK, EVA is a notifiable disease, which means that anyone who owns, inspect or manages a horse must notify the DEFRA when they suspect an animal to be infected with EVA or a stallion to be a shedder.
Unfortunately, because of the variability of clinical signs, only a blood test is reliable to diagnose that your horse has EVA. The blood test tests for antibodies against the EVA virus, which is the bodies response to the virus, and can screen for the actual virus as well. To test if a stallion is a ‘shedder’, in addition to a positive blood, the semen of the stallion would be tested twice, at least 7 days apart. If the semen does contain the virus, this would confirm that the stallion is a shedder.
Preventing and controlling EVA
Because EVA is a notifiable disease, routine vaccination would complicate being able to identify horses with a current infection, because both would have antibodies against EVA in their blood. Routine vaccination is therefore only advised for stallions, particular from the continent. This to prevent breeding stallions becoming ‘shedders’.
If your horse is to be inseminated and the semen is imported from the continent then it should be accompanied by a health certificate stating that the semen is taken from a stallion, tested and proven negative to be a shedder for EVA. For semen that comes from inside the United Kingdom, there will be no official health certificate although it’s advisable to check for the stallion’s EVA status.