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April 8, 2011

Plague death uncovered

The death of University researcher Malcolm Casadaban caused a stir in September 2009 when it emerged that he had been working with a weakened strain of Yersinia pestis, the bacterial agent of the plague.

However, a recent Morbidity and Mortality Weekly Report released by the Centers for Disease Control and Prevention (CDC) painted a more complicated picture of the cause of death.

According to the February 25 report, Casadaban was particularly susceptible to the plague because of his hemochromatosis.

“When you deal with an attenuated organism...they are attenuated for most people but not for everybody,” said Dr. Ken Alexander, Chief of Infectious Disease at the U of C pediatrics department and a member on the emergency panel called after Casadaban’s death.

Y. pestis requires the presence of iron in order to be virulent, and the CDC-approved strain that Casadaban was researching lacked a series of iron-binding and metabolizing proteins.

Due to his hemochromatosis, however, Casadaban had unusually high levels of iron in his body, which allowed the otherwise non-virulent strain to become fatal.

“These bacteria, which normally are not very good at finding iron...found in him a rich and easy source of iron,” Alexander said.

Hemochromatosis is fairly rare, with the condition affecting roughly one in 300 Americans, according to the CDC. According to Alexander, researchers had not considered the disease a risk factor until Casadaban’s death.

Still, how the bacterium got into his blood remains a mystery. According to the report, Casadaban did not attend all of the required safety procedure classes and did not consistently wear gloves while handing Y. pestis.

According to Alexander, this constituted a breach of safety protocol, but it’s unclear whether it contributed to his death. “You can always prevent something in retrospect,” he said.

The University has made no changes to laboratory procedures in response to Casadaban’s death. The circumstances surrounding Casadaban’s death comprised a “perfect storm,” and policies are not changed based on an aberration, Alexander said.

Casadaban, an assistant professor of genetics and cell biology at the University, was unaware of his condition.

While hemochromatosis was suspected just days after Casadaban’s death, the CDC report was published almost a year and a half later, partly because multiple tests were required to confirm that the strain found in Casadaban’s blood was the attenuated strain.

Casadaban contracted the septicemic plague, a variant of plague which afflicts the blood and is more deadly than the bubonic kind.

According to the CDC, there are an average of 5 to 15 cases of plague reported each year in the United States, mostly in the rural Southwest. If diagnosed and treated, mortality for the disease is 15 percent. If untreated, mortality ranges from 50 percent to 90 percent.

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