American Board of Internal Medicine (ABIM) Certification Practice Exam

Where is babesiosis most commonly found?

1. The coastal southeastern United States

2. The coastal midwestern United States

3. The coastal northeastern United States

4. The inland southwestern United States

The correct answer is: The coastal northeastern United States

Babesiosis is a tick-borne disease caused by the parasite Babesia, which most commonly affects red blood cells. The geographical distribution of babesiosis is closely linked to the habitat of its primary vector, the Ixodes scapularis tick, commonly known as the black-legged tick or deer tick. This disease is most prevalent in the coastal northeastern United States, particularly in areas such as New York, New Jersey, Massachusetts, and Connecticut. The ecology of these regions supports the life cycle of both the tick and the reservoir hosts, primarily deer and rodents, which are critical for the maintenance of the Babesia parasite. In contrast, the other regions mentioned do not have the same environmental conditions or tick populations conducive to the transmission of babesiosis. The coastal southeaster and midwestern United States and the inland southwestern United States may have different types of ticks and wildlife, but they are not recognized as areas where babesiosis is endemic. Therefore, the coastal northeastern United States is clearly identified as the region with the highest incidence of this disease.