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Causes
By Mayo Clinic staff
In the United States, Lyme disease is caused by the bacterium Borrelia burgdorferi, which is carried primarily by deer ticks. The ticks are brown and often no bigger than the head of the pin, which can make them nearly impossible to spot.
Ticks feed on blood, attaching to a host and feeding until they're swollen to many times their normal size. During feeding, ticks that carry disease-producing bacteria can transmit the bacteria to a healthy host. Or they may pick up bacteria themselves if the host is infected. In areas where Lyme disease is common, as many as 50 percent of deer ticks may carry Borrelia burgdorferi.
Deer ticks typically feed on the blood of mice, small birds and deer, but they can also feed on the blood of humans, cats, dogs and horses. They live in low bushes and tall grasses of wooded areas, waiting for warmblooded animals to pass by. Deer ticks are most active in the summer.
To contract Lyme disease, you must be bitten by an infected deer tick. The bacteria enter your skin through the bite and eventually make their way into your bloodstream. Before bacteria can be transmitted, a deer tick must take a blood meal and that can take more than 48 hours of feeding. Only ticks that are attached to your skin and are feeding can transmit the bacteria. An attached tick that has a swollen appearance may indicate that enough time has elapsed to transmit bacteria. Removing the tick as soon as possible may prevent infection.
