The pathogen for this patient's presentation?

A 34-year-old man develops a flu-like illness that is accompanied by a red, flat, round rash on his leg that progressively expanded outward over the course of a week. As the rash expanded, the center of the rash slowly turned clear. What was the most likely event that introduced the pathogen for this patient’s presentation?

Airborne droplet inhalation
Fecal-oral ingestion
Tick bite
Unprotected sexual contact

Correct answer
Tick bite
correct answer: D

The rash described is erythema chronicum migrans (ECM), the primary lesion of Lyme disease, which is caused by Borrelia burgdorferi. A tick bite (choice D) from the Ixodes tick transmits the spirochete from the white-footed mouse reservoir, and the illness starts about 10 days after the bite with a single ECM rash, a flu-like illness, and regional lymphadenopathy.

Lyme disease is not transmitted via airborne droplets, fecal-oral, needle-sticks, or unprotected sexual contact.