A 36-year-old man presents at his physician’s office complaining of fever and headache. On examination, he had leukopenia and increased liver enzymes, and inclusion bodies were seen in his monocytes. History revealed that he was an outdoorsman and remembered removing a tick from his leg. Which of the following diseases is most likely causing the symptoms described?

**Core Concept**
The question is testing the student's ability to identify a tick-borne disease based on clinical presentation and patient history. The underlying concept is the pathophysiology of tick-borne illnesses, particularly those caused by Rickettsia and Borrelia species.

**Why the Correct Answer is Right**
The patient's symptoms, including fever, headache, leukopenia, and increased liver enzymes, are consistent with an acute infection caused by Borrelia burgdorferi, the causative agent of Lyme disease. The presence of inclusion bodies in monocytes is a characteristic feature of Lyme disease. The patient's history of tick removal from his leg further supports this diagnosis. The tick-borne pathogens, such as Borrelia burgdorferi, invade the host cells and cause cellular damage, leading to the observed clinical symptoms.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ehrlichiosis, caused by Ehrlichia chaffeensis, typically presents with fever, headache, and thrombocytopenia but without inclusion bodies in monocytes.
* **Option B:** Anaplasmosis, caused by Anaplasma phagocytophilum, also presents with fever, headache, and thrombocytopenia but without characteristic inclusion bodies in monocytes.
* **Option D:** Rocky Mountain spotted fever, caused by Rickettsia rickettsii, presents with fever, headache, and rash but typically does not involve leukopenia or liver enzyme elevation.

**Clinical Pearl / High-Yield Fact**
Inclusion bodies in monocytes are a hallmark of Lyme disease, and tick removal history is crucial in making this diagnosis. This is a classic exam trap, as other tick-borne diseases may present similarly but lack characteristic inclusion bodies.

**Correct Answer:** C. Lyme disease.

✓ Correct Answer: B. Ehrlichiosis