A 50-year-old woman presents with intermittent fever, a recurrent generalized headache, and malaise and fatigability for two weeks. Close questioning reveals the presence of a reddened painless lump on her right arm, for around the same duration.
Three weeks ago, she returned from a one-month vacation in Costa Rica, where she engaged in numerous outdoor activities, including hiking, rock climbing, swimming in rivers, and snorkeling. There is no history of unsafe sexual contact or intravenous drug abuse.
Her medical, surgical, drug, and allergic histories are unremarkable. She is unmarried, has no children, and lives alone.