It's from a tick bite. The tick's are just carriers really, the desease comes from mice.(more on this) Starts out with flue-like symptoms and if it goes undiagnosed for a long time came be quite debilitating. It can hide in organs going undetected for a long time untill enough damage is done. Cronic fatigue, swollen joints, nervous system damage, organ damage including your heart.
Caught and treated early enough it's usually no problem. I'm lucky I noticed the bite mark and kept an eye on it. It did go to the classic bulls eye about 6" in diameter, thats when I went to the Doc and blood test confirmed it.
...My second time going down this road. 1st time was 8 or 10 years ago.
The only negatives now is a persistant headache and a little stomach upset from the antibiotics. Small price to pay to get rid of it. I have been lazy about using repellant this summer, so I have nobody to blame but me.
As far as the desease's origin, it's rumored to have been developed by man, in a lab off of Ct during WW2 by scientist experimenting with bio warface stuff. It's name Lyme, comes from the area in Ct where it first started showing up. (if you believe in conspirocy theories) Who knows