lisar1969 wrote:
My neighbor boards 2 horses for a friend of hers. They had never been vaccinated when he bought them. He vaccinated both as soon as he moved them in and BOTH came down with PHV. They are recovering, (it's been months!) both are still thin and one is lame off and on. I don't know how much it cost him in vet bills. Neighbor said they almost lost both of them. She also told me the vet said they got sick from the vaccine and that it wasn't contagious. I thought it was contagious but spread through insect bites?
No, it's very unlikely the horses got PHF from the vaccine. As I mentioned, the vaccine is not entirely effective. There are around 6 identified strains of the disease-causing organism, and the vaccine only protects against one. I've heard rumors of a more complete vaccine becoming available.

The disease is caused by a organism that lives in mayflies and other aquatic flying insects. Horses accidentally ingest the insects when grazing or drinking and therefore the parasite. A local barn here had PHF in December once: some bugs had gotten rolled into the hay.