The disease is transmitted in a unique way, i.e., the bite of the deer tick. Although the disease has only one vector (disease-carrying organism), deer tick is the most commonly found type of tick, which makes the propagation of Lyme disease quite easy. It is usually not fatal, though foals are more at risk. But if left unchecked, Lyme disease in horses can lead to liver damage, hepatitis and severe encephalitis, causing drastic behavioral changes.