The last weeks of Oliver Cromwell's life were marked by a roller coaster of illness. From the beginning of August 1658, the man who (briefly) abolished the British monarchy complained of sharp bowel and back pains. He suffered from insomnia, cold and hot fits, sore throat, cough, confusion, diarrhea and vomiting. He would get worse and then seem like he was recovering, but by the end of the month, his fever gave his attendants "the sadde apprehension of danger." He died suddenly in London at age 59.

Cromwell's doctors at the time were unable to come up with a precise cause of death. Of course, that hasn't stopped other people from coming up with their own diagnoses in the intervening centuries. Suspicions have ranged from the mundane — infected kidney stones — to the conspiratorial — poisoning by a closeted Royalist doctor.

Now, one doctor has a new theory for what killed one of Britain's most controversial figures: a lethal combination of malaria and typhoid fever caused by a Salmonella infection. [8 Grisly Archaeological Discoveries]

While historians have suspected that Cromwell was suffering from a bout of chronic malaria (a mosquito-borne infectious disease) before he died, Dr. Sanjay Saint, a professor of internal medicine at the University of Michigan, does not think it was malaria that ultimately killed him.

"What physicians usually try to do is use Occam's razor, saying that one diagnosis explains it all," Saint told Live Science. "In this particular case, I think that Occam's razor is dull, and I'm invoking Hickam's dictum, which states that a patient can have as many diseases as he darn well pleases. I think that Oliver Cromwell had two diseases. I think that he had malaria, and I think that on top of that, he had typhoid fever, which ended up killing him."

Cromwell's legacy is still disputed today. Some see him as the father of British democracy who toppled the monarchy, while others think of him as a war criminal (especially in Ireland) for his anti-Catholic policies and military campaigns. After leading the Parliamentarians to victory over the Royalists in an English civil war and executing King Charles I, Cromwell ascended to power in 1653 as Lord Protector of the Commonwealth of England, Scotland and Ireland, serving until he died five years later.

To reassess Cromwell's death, Saint looked at the records left by his doctors and associates. During the embalming of Cromwell, examiners found that his brain had overheated, his lungs were engorged, and his spleen, while of normal size, was filled with matter that looked like the "Lees of Oyl," or the big deposits of oil that might settle at the bottom of a jar, something that is characteristic of a septic spleen, Saint said.

Saint thinks these symptoms are consistent with typhoid fever, which was common in the 17th century and is acquired from fecal-oral transmission, usually when a person eats food or drinks water contaminated with the Salmonella typhi strain of bacteria. This bacterial infection can lead to the thinning of the intestinal wall, which can give way to a rupture, releasing various microbes into the bloodstream, overwhelming the body and causing sudden death.

Saint was asked to review Cromwell's case for the Historical Clinicopathological Conference, which is being held today (Oct. 23) at the University of Maryland School of Medicine. Each year at this meeting, doctors revisit the death of a historical figure. For example, in 2007, diagnosticians at the conference determined that Abraham Lincoln may have survived his gunshot wound if he had been wheeled into a modern emergency room.

"One of the most exciting parts about being a physician is that you get to be a detective — that's why many of us go into internal medicine," Saint said. "It makes it more challenging to understand why someone died when you cannot examine them or ask questions or perform any tests on them."

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