Erythema migrans is a skin lesion associated with which infection after a tick bite?

• A. Rocky Mountain spotted fever
• B. Ehrlichiosis
• C. Lyme disease
• D. Anaplasmosis

Answer: (C)

Erythema migrans is the hallmark early skin finding of Lyme disease caused by Borrelia burgdorferi transmitted by Ixodes ticks. The rash begins at the bite site and expands outward, often with central clearing, giving a bull’s-eye appearance. This expanding annular lesion signals Lyme disease and helps differentiate it from other tick-borne illnesses, which do not produce this characteristic pattern. For example, Rocky Mountain spotted fever usually presents with fever and a rash that starts on the wrists and ankles and may involve the palms and soles, not a single migrating lesion; ehrlichiosis and anaplasmosis present with fever and malaise and rash is less common, not the distinct migratory ring.