On September 13, 2009, Malcolm Casadaban, a University of Chicago professor of genetics and cell biology, was taken by ambulance to a hospital and died just a few hours later. Cause of death: The Plague, with a capital P.
Casadaban had been working with Plague bacteria as part of his research, but, despite that fact, this wasn't an open-and-shut case. Casadaban's bacteria were genetically modified, weakened so they couldn't infect humans. Scientists have been handling this sort of wishy-washy Plague for decades, without much incident. Until Casdaban, no-one had ever been killed by lab-acquired Plague. In fact, 1959 was the last time lab Plague had even made anyone sick.
The Centers for Disease Control wanted to know what made Casadaban different. And this is where the story gets weird. Turns out, Casadaban had his own weakness—a genetic mutation, common in people of European descent. In fact, this particular mutation is common because it protects against naturally acquired strains of the Plague. If your ancestors lived through a Plague outbreak, you're more likely to carry it. But, the same mutation also seems to leave you particularly susceptible to weakened, laboratory Plague bacteria.
An autopsy found the researcher had a medical condition called hemochromatosis, which causes an excessive buildup of iron in the body, according to the CDC report. The disorder affects about 1 in 400 people and goes unnoticed in about half of patients.
Casadaban's illness is important because of the way the plague bacterium had been weakened. Yersinia pestis needs iron to survive. Normally it gets this iron by stealing it from a host's body with proteins that bind to it and help break it down. To make the bacterium harmless, scientists genetically stripped it of the proteins needed to consume iron.
"It's like having a lion, where we took out all its teeth and all its claws," Alexander said. "But in the case of Dr. Casadaban, the lion didn't even need to have teeth. There was so much iron that it was freely available and easy to get."
The hemochromatosis that contributed to Casadaban's fate has been credited with protecting people from strains of plague that circulate in the wild. Sharon Moalem, an evolutionary biologist and author of "Survival of the Sickest," posited that the disorder shifts iron from certain white blood cells, where it is typically sought by the plague bacterium.
Morbidity and Mortality Weekly Report: Fatal laboratory-acquired infection with an attenuated Yersinia pestis strain—Chicago, Illinois, 2009
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.