In august of 2012 I got a new mini mare. She was checked and had a healthy appearance. In spring of 2013 she had biting lice which I treated her and her buddy along with the barn. I have 2 small barns. Well the lice has appeared again and I am treating again. So far it is isolated to the barn she is in. I have read all that I can find on lice and horses, been able to identify the type of lice but I have not been able to find how it spreads. So far I have it only on 2 horses in the same barn. The other 5 in my 2nd barn do not have lice. I have kept the horses that have lice isolated from the others. How does this pest spread to other horses? I only see it in the spring or am I not getting all the eggs?