It's spread by the lone star tick. Especially a concern if you live in a wooded area frequented by bobcats, since they are an asymptomatic reservoir species.
We lost our 7yo healthy kitty to it this past June. He was almost entirely an indoor cat, but we have dogs and my son runs trails. One of those two parties probably brought the tick inside the house.
I lost a sweetheart of a kitten to bob cat fever a few months ago. Vaccinated for everything except that.