I'd like to add a comment on quarantine, for those who are reading this and looking for information. Many equine illnesses have a incubation period of up to two weeks. I believe Strangles might be one of them. EHV also can take a few days to show. A horse may appear perfectly healthy, but is harboring a incubating illness. FYI, the human common cold has an incubation period of about 3 days. Chicken Pox is about a week, I think. Anyway, a health certificate just certifies that the horse appears healthy at that time. His temp and breathing, gums etc appear healthy. There are many vets who issue health certifs without even taking a temp or listening to the lungs. In order to protect the health of my existing horses, my vet recommends an incubation period of two weeks. The dogs are even prevented from sniffing the new horse as the saliva from the new horse can easily get on the dog's fur and then the dog goes and says hello to your other horses.
Bringing two new horses into my barn (they were body clipped) during one winter, caused illness in about 15 other horses and $13,000 - yes< THIRTEEN THOUSAND DOLLARS!!! - in vet bills. Of course, I didn't need to call the vet, I could have let nature take it's course, but I would have had at least 2-3 dead horses and lost foals. Don't ever think this will never happen to you, it can and will. Oh, I also fed those horses last and used Purel afterwards. They also had health certificates and negative Coggins. They came from a reputable breeder, who I don't blame at all. It just happens.