What killed Charles Darwin?

It's always interesting to me when researchers try to diagnose the ailments of famous historic figures based on reported symptoms. The Historical Clinicopathological Conference does just that every year. This year, the conference focused on Charles Darwin, narrowing down his then-mysterious collection of symptoms to probably being attributable to one of three ailments: cyclic vomiting syndrome, Chagas disease, or peptic ulcers. Of the three, I'm particularly fascinated by the idea of Darwin with Chagas, a parasitic infection that can cause heart failure over many years. If that were the case, it would mean the naturalist picked up the disorder that killed him while on the South American travels that eventually made him famous.