A 37-yr old male comes into the emergency room complaining of fever, chills, diarrhea, headaches, weakness, and fatigue. He had a similar bout of symptoms 2 days earlier, but then they disappeared and he felt better. Now the symptoms have returned. When you draw his blood you find that he is severely anemic—that is, he has very few red blood cells. He has just returned from a subtropical region in Africa, where he had a fabulous time, although he has nothing nice to say about the blood-sucking mosquitoes they have there. In passing, he mentions that his regular doctor had given him some chloroquine pills to take during his trip, but he had forgotten to take them with him. What does the man have and what is one causative agent?