There are many different types of ticks in the United States, some of which are capable of transmitting infections. The risk of developing these infections depends upon the geographic location, season of the year, type of tick, and, for Lyme disease, how long the tick was attached to the skin.
While many people are concerned after being bitten by a tick, the risk of acquiring a tick-borne infection is quite low, even if the tick has been attached, fed, and is actually carrying an infectious agent. Ticks transmit infection only after they have attached and then taken a blood meal from their new host. A tick that has not attached (and therefore has not yet become engorged from its blood meal) has not passed any infection. Since the deer tick that transmits Lyme disease must feed for >36 hours before transmission of the spirochete, the risk of acquiring Lyme disease from an observed tick bite, for example, is only 1.2 to 1.4 percent, even in an area where the disease is common.
The organism that causes Lyme disease, Borrelia burgdorferi, lies dormant in the inner aspect of the tick's midgut. The organism becomes active only after exposure to the warm blood meal entering the tick's gut. Once active, the organism enters the tick's salivary glands. As the tick feeds, it must get rid of excess water through the salivary glands. Thus, the tick will literally salivate organisms into the wound, thereby passing the infection to the host.