You are answering a USMLE-style medical question. Question: A 21-year-old male presents to his primary care provider for fatigue. He reports that he graduated from college last month and returned 3 days ago from a 2 week vacation to Vietnam and Cambodia. For the past 2 days, he has developed a worsening headache, malaise, and pain in his hands and wrists. The patient has a past medical history of asthma managed with albuterol as needed. He is sexually active with both men and women, and he uses condoms “most of the time.” On physical exam, the patient’s temperature is 102.5°F (39.2°C), blood pressure is 112/66 mmHg, pulse is 105/min, respirations are 12/min, and oxygen saturation is 98% on room air. He has tenderness to palpation over his bilateral metacarpophalangeal joints and a maculopapular rash on his trunk and upper thighs. Tourniquet test is negative. Laboratory results are as follows: Hemoglobin: 14 g/dL Hematocrit: 44% Leukocyte count: 3,200/mm^3 Platelet count: 112,000/mm^3 Serum: Na+: 142 mEq/L Cl-: 104 mEq/L K+: 4.6 mEq/L HCO3-: 24 mEq/L BUN: 18 mg/dL Glucose: 87 mg/dL Creatinine: 0.9 mg/dL AST: 106 U/L ALT: 112 U/L Bilirubin (total): 0.8 mg/dL Bilirubin (conjugated): 0.3 mg/dL Which of the following is the most likely diagnosis in this patient? Options: A) Chikungunya B) Dengue fever C) Epstein-Barr virus D) Hepatitis A Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.