Then 'why' are there the ticks that cause this disease?
Personally, I believe that's how ecology works.
Something fills a niche, and something else tends to keep it in check.
That's one of the reasons some scientists are concerned, human beings have often been culled by disease when there are a lot of us.
Some scientists say it's just a matter of time, given how well viruses etc evolve, that one day something will dramatically reduce our numbers.
It's happened before, but now there are many more of us.
Lyme disease is just a bacteria that has evolved to survive with ticks.
http://www.nhs.uk/Conditions/Lyme-disease/Pages/Introduction.aspx#diagnosisThe reason it exists is it has evolved into a ecological niche, just like the rattlesnake.
Some people see an order in ecology, how the system works, how animals adapt etc. Some call the order God or proof of God.
Some find it too ordered to have happened randomly
Others don't.
It's in the eye of the beholder.