Body Lice Possibly Contributed to Rapid Spread of Bacteria in the Bubonic Plague, Study Reveals

Scientists have long argued whether human body lice played a part in the quick transmission of the microorganism accountable for the Black Death in the Middle Ages.

Although rat fleas are known to have been a primary cause, some population studies recommend that their bites alone may not have caused the contagion that killed tens of millions in Europe, Asia, and other regions in the 14th century.

Body Lice Contributed to Bubonic Plague

Research circulated in PLOS Biology on Tuesday signifies that body lice may be more efficient at spreading the plague bacterium, Yersinia pestis, than formerly believed, possibly adding essentially to the bubonic plague pandemic.

Body lice, which are different from the more typical head lice that commonly affect school-age children in the U.S., are parasites that spread disease and usually pester people in congested situations. Both types of lice feed on human blood.

"There's a long-standing medical historical debate about the Black Death pandemic in Europe," said Joe Hinnebusch, the study's senior author and former senior investigator at the National Institute of Allergy and Infectious Diseases Laboratory of Bacteriology. He is now retired.

Hinnebusch noted that some studies examining the rapid spread of the plague in the Middle Ages have suggested that another blood-sucking insect might have been involved.

Initially, researchers considered human fleas but found they were not effective in spreading the bacteria. The focus then shifted to body lice.

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Researchers Studied Blood Samples in Body Lice 

In their experiments, the researchers allowed body lice to feed on blood samples infected with Yersinia pestis using an artificial skin model. The lice became infected and, when later placed on another piece of artificial skin to feed on sterile blood, they transmitted the bacteria, which was detectable in the formerly sterile blood sample.

"You could see transmission as early as day one, but more bacteria were transmitted on days three to seven after infection," Hinnebusch said.

Although plague cases are infrequent in the U.S. today, with one to 17 cases reported yearly, mostly in the rural West, the CDC notes that the bacteria possibly arrived in the U.S. around 1900 via rat-infested ships.

Dr. Meghan Brett, an associate professor of infectious diseases at the University of New Mexico, noticed that the new research might shed light on how the plague spread so widely in the Middle Ages, causing 30% to 50% fatality. She noted that the role of rats and fleas alone had been inadequate to clarify the pandemic's reach, making this research essential.

Dr. William Schaffner, a professor of infectious diseases at Vanderbilt University Medical Center, pointed out that although the research was managed in a lab setting, it shows that body lice can indeed spread plague bacteria. However, it remains ambiguous how many real-life infections were due to body lice.

In the U.S., people commonly contract the plague through bites from prairie dog fleas while hunting or hiking. Infected people experience swollen lymph glands in the groin, and prompt antibiotic medication can cure the virus. However, penetration of the bacteria in dusty environments can result in serious pneumonia, which can be deadly within days.

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