What is the most common vector-borne zoonotic infection in the United States?

• A. Lyme disease
• B. Ehrlichiosis
• C. Rocky Mountain Spotted Fever
• D. Tularemia

Answer: (A)

This question tests knowledge of which vector-borne infection occurs most frequently in the United States. Lyme disease, transmitted by Ixodes ticks carrying Borrelia burgdorferi, has the highest incidence among vector-borne zoonoses in the U.S. Its ticks are widespread across the Northeast and upper Midwest, and outdoor exposure in these regions leads to many cases each year. Clinically, early Lyme disease often presents with erythema migrans and systemic symptoms, and if untreated can progress to arthritis or neuropathies, highlighting its impact. Other tick-borne infections exist, such as ehrlichiosis, Rocky Mountain spotted fever, and tularemia, but their overall case numbers are much lower than Lyme disease, making Lyme disease the most common vector-borne zoonotic infection in the United States.