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Lyme disease is caused by the bacteria Borrelia burgdorferi, which is transmitted by the bite of infected Ixodes ticks. In the United States, Lyme disease is common in the northeastern states, Atlantic coastal states, and the upper Midwest. Infections occur most often in late spring and summer when ticks are most prevalent. Generally, Lyme disease is uncommon in the Pacific Northwest. In Washington state it occurs primarily in the western half of the state.


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