The original animal was discovered because its owner was taking it out of the state. We don't know where these animals got infected. It can make the horse virtually worthless as it doesn't have much strength or stamina. Basically the disease diminishes the worth of the horse and the value to the owner. There are essentially three degrees of EIA infectiousness.
Some horses exposed to the virus develop acute symptoms and die within two to three weeks.
Others develop a chronic condition that is often marked by lethargy and anorexia. But a majority of horses with the disease are called inapparent carriers, surviving as reservoirs of the infection. They are the biggest concern. So no one does anything to prevent contact with other horses and that can be a real problem. If you know your horse is sick, chances are the animal is not going to travel and won't be exposed to other horses.