You are in Uganda doing an international elective and you see the patient shown above. He comes in because of the painful lesion on his shoulder which he got while traveling through warm shaded forests in a large blue van (with open windows). On examination, the lesion is rubbery, painful, and indurated. You are unsure what it is and tell the patient to return in a week.
In a week, the patient presents again with intermittent headaches, fevers, malaise, and arthralgias. On exam, the patient has soft painless posterior cervical lymphadenopathy and splenomegaly.
Challenge: The diagnosis is lethal if untreated, so you better know what it is before it progresses to the next stage. (What's the next stage?)
Image is in the public domain.