Lyme disease in the US is caused by the spirochete Borrelia burgdorferi, which is transmitted to humans by Ixodes scapularis (blacklegged [deer] tick) and I. pacificus (western blacklegged tick). Most cases of Lyme disease occur in late spring and early summer in northeastern and mid-Atlantic states, the upper Midwest, and in northern California. B. mayonii, which is also transmitted by I. scapularis, has been shown to cause a similar illness in the upper Midwest.

With increasing travel, immigration, use of immunosuppressive drugs and the spread of AIDS, physicians anywhere may see infections caused by parasites. The table in this document lists first-choice and alternative drugs for most parasitic infections.

Patients who receive pretravel advice can reduce their risk for many travel-related conditions. Vaccines recommended for travelers are reviewed in a separate issue.