A 32-year-old trekker returns from a forested area in Europe with fever, headache, and an annular red plaque on the thigh with central clearing that has expanded from 2 cm to 12 cm over a week. He recalls a tick bite at that site. What is the causative agent and its vector?

• A Borrelia recurrentis, Pediculus humanus corporis
• B Leptospira interrogans, contaminated water
• C Borrelia burgdorferi, Ixodes tick ✓
• D Rickettsia conorii, dog tick

Explanation

Erythema migrans, an expanding annular lesion with central clearing appearing days to weeks after a tick bite, is the hallmark of stage 1 Lyme disease caused by Borrelia burgdorferi, transmitted by Ixodes ticks. Relapsing fever borreliae cause recurrent febrile episodes without a persistent expanding skin lesion. Leptospirosis follows water exposure and causes conjunctival suffusion and jaundice, while R. conorii produces an eschar and maculopapular rash rather than erythema migrans.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.