Lyme disease is an increasingly prevalent tick-borne disease. It is difficult to definitvely diagnose as most of our affordable testing options only measure exposure. Treatment, vaccination and long-term testing regimens are controversial. If you ever want to see a heated debate amongst veterinarians, go to a continuing education talk on Lyme disease. It can get pretty brutal. Both of my dogs have been exposed to Lyme. I waited to treat them until they showed symptoms of fever, lameness and lethargy. Luckily they responded well to therapy.
It's true that the majority of cases are found in the northeastern region of the United States but that range is growing. Even if you don't live in this part of the country it is important to know about this disease as you may come across patients with a travel history to this region. Here is an interesting article on Lyme disease from Penn warning about the increase in new positive patients.
https://pavma.wordpress.com/2015/08/19/lyme-disease-is-a-serious-threat-get-prepared/