Bite of infected tic. Lime disease is spread by ticks that have acquired the germ in the past and it stays in their system. A tick bite from another of the same species without the ld germ will not do it. The tick must get on your body, settle in for a feeding & feed long enough to pass the germ to you (hours).
Tick, fly bites &... Most lyme is from bites of the deer tick but half of those with lyme don't recall a tick bite; undoubtedly many were bitten & did not know it. It has also been shown to be caused by fly bites- see http://www.Nejm.Org/doi/full/10.1056/nejm199006143222415 some feel lyme may be spread by mosquitoes, spiders, sexually & mother to baby but these are unproven; i feel mother to baby is likely in some.