My pet theory is that lyme disease coevolved to make mamals "addicted" to ticks. Every reinfection and the resulting fever-body pyrolysis, resets the infections malaise sideffects for a while. Thus, if you where outside all the time, you would be conditioned to expose yourselfs to ticks all the time, to feel "healthy" again. If those little bastards secreted fentanyl it would have a similar outcome.