As my colleagues mention, lyme disease
is caused by a bacteria
, borrelia burgdorferi, & is commonly thought to be transmitted by deer ticks.
However, half of those proven to have lyme don't recall being bitten by a tick. It is proven that lyme can be transmitted by biting flies & possibly by mosquitoes, fleas, spiders etc. It can be transmitted in utero to babies & probably sexually. See comment.