Review Question - QID 212841

A 33-year-old man presents to the emergency department with a fever and fatigue. He states that he has not felt well since he returned from a hiking trip in Alabama. He is generally healthy and has no other medical conditions. His temperature is 101°F (38.3°C), blood pressure is 127/85 mmHg, pulse is 108/min, respirations are 14/min, and oxygen saturation is 99% on room air. Physical exam including a full dermatologic inspection is unremarkable. Laboratory studies are ordered as seen below.

Hemoglobin: 13 g/dL
Hematocrit: 39%
Leukocyte count: 2,200/mm^3 with normal differential
Platelet count: 77,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 24 mEq/L
BUN: 19 mg/dL
Glucose: 98 mg/dL
Creatinine: 1.3 mg/dL
Ca2+: 10.2 mg/dL
AST: 92 U/L
ALT: 100 U/L

Which of the following is the most likely diagnosis?