A 28-year-old male factory worker from Chennai presents with a 3-week history of progressive weight loss (7 kg), persistent fever (38.5–39.2°C), and profuse night sweats drenching his clothes. He also complains of dyspnea on exertion and palpitations. On examination, he is cachectic with warm, moist skin. His resting metabolic rate (measured by indirect calorimetry) is 45% above the predicted normal value. Chest X-ray shows no infiltrates. Thyroid function tests are normal. Serum salicylate level is undetectable. A urine dipstick shows 2+ proteinuria. Which of the following is the most likely explanation for his hypermetabolic state and clinical presentation?