Malcolm Casadaban, a 60-year-old genetics and cell biology professor, was conducting laboratory research on Yersinia pestis, the bacterium that causes the plague — yes, that plague — when he got sick — but no one was too worried, because he was working with a harmless strain:
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.
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.
People of European descent are twice as likely as the rest of the population to have hemochromatosis, according to previous studies. That’s because people with the condition were more likely to survive epidemics of the bubonic plague that killed millions of people in medieval Europe and pass the hereditary condition to their descendants, according to Moalem.
The day plague was diagnosed in Chicago, researchers tested the strain to make sure it hadn’t mutated. By a second emergency meeting that afternoon, high amounts of iron had already been discovered in Casadaban’s liver, adding credibility to the early hypothesis of hemochromatosis formed by his colleagues.
The CDC later confirmed the tests with mouse experiments that proved the strain that killed Casadaban was the same that has been safely used by hundreds of scientists doing similar research. The agency is now studying animals to learn how hemochromatosis may increase susceptibility to infection by bacteria with weakened iron-acquiring abilities.
Casadaban’s death shows that no matter how a germ has been hobbled, some people may always be vulnerable, Alexander said.