I lived in Vermont prior to moving here to Kansas 3 (4?) years ago. Ticks went from pretty non-existent to hordes although some specific areas interestingly remained somewhat tick free. Over the years I had many dogs diagnosed with lyme, a couple with anaplasmosis and one with ehrlichia. My terrific vet saw a lot of tick disease in his clients and after thought and research he decided that it was best to treat if testing positive. His thinking was don’t give the spirochetes the time to get comfortable and settled into the body because he felt that was when more severe and chronic problems arose. That thinking seems on target with human exposure too. People who recognize early symptoms and quickly start a full month of meds seem to usually be fine whereas the people who didn’t even know they had a tick bite and were ill for months or years before diagnosis seemed to have more difficulty. My dogs who contracted Lyme in the early days before we had/knew about testing had symptoms and a couple had chronic problems but the later ones who were treated quickly showed no symptoms.
Once Frontline came on the market I found a big decrease in disease in my dogs. I continue to use it when I grouse hunt and my dogs have been testing clear. I, however, came down with Lyme symptoms last winter a few weeks after grouse hunting in MN. I immediately started doxy for a month, symptoms quickly disappeared and I have been fine since.