This is now becoming a common, and potentially fatal, type of equine adult diarrhea in Ontario. It is transmitted by insects. Each year, our veterinarians are now treating cases within our practice. We are also aware that the Ontario Veterinary College is starting to admit more cases every year as well.
The Potomavac line of vaccines will provide some protection against severe disease, with vaccinated horses being less likely to die from infection. However, at this point in time, the vaccine has a short duration of immunity, losing it effectiveness after 3 months. Your horse will require two annual doses to fully protect them during the risk period from May to October. If this is the first year you have decided to protect your horse against Potomac Horse Fever, we would recommend starting with a dose of Potomavac + Imrab along with their other spring vaccines. This will protect them against both Potomac Horse Fever and Rabies. They will require a booster shot of Potomavac (without Imrab) 4 weeks later.
We would recommend you complete the booster series by May, in order for your horse to be protected from May to July. We would then recommend a third booster in August, which will protect your horse for the remainder of the risk period from August to October.