Summer and fall are key seasons for the appearance of Potomac horse fever, which is caused by the bacterium Neorickettsia risticii. Don't be fooled by the name; Potomac horse fever originally was identified in 1979 as a sporadic disease affecting horses residing in the eastern United States near the Potomac River, but since that time it has been diagnosed throughout the United States and Canada. "Don't ignore fevers," warned Nathan Slovis, DVM, ...