Rat Fleas Not the Only Culprits, Lice Also Implicated in Spreading ‘Black Death’ Plague


The infamous Black Death, a mid-14th century plague, was relentlessly catastrophic. It wiped out millions throughout Europe in just a few decades. Most believe rat fleas were the main culprits in transmitting the lethal Yersinia pestis bacterium, but recent studies suggest that human body lice also had a big part to play in the spread this plague.

How Rat Fleas Transmit the Plague

Rat fleas transferring Yersinia pestis from wild rodents to humans is a classic contagion route for plagues. Joe Hinnebusch, a retired microbiologist from the National Institute of Allergy and Infectious Diseases explained that fleas ingest this bacterium when they bite diseased rodents. When their rodent hosts die, these fleas then infect humans and other small animals by biting them.

Human Body Lice’s Potential Role in the Spread of the Plague

Rat fleas have been widely blamed for spreading plague, but new research proposes that human body lice might also have had a significant role in disseminating this disease. Human body lice transmission is not uncommon as demonstrated by diseases like relapsing fever and these insects were prevalent during poor hygiene conditions common during middle-ages.

Dr. Gene Kritsky, an entomologist has been studying insect behaviors along with his team. Their research published in PLOS Biology indicates that human body lice’s is likely more efficient transmitters of Yersinia pestis than what was previously assessed.

Recent Discoveries from Lab Investigations

The study involved feeding lice with blood infected with Yersinia pestis and observing bacterial activity within the lice. The team found out that bacteria live comfortably in lice gut and invaded the salivary glands in lice’s known as Pawlowsky glands. Presence of this deadly bacteria in these glands shows possible efficient transmission when lice’s bite humans.

Differing Opinions and Controversy

The role of human body lice’s in spreading the plague is hotly contested. While Kritsky present compelling proof, some experts insist that rat fleas are the primary carriers mainly due to their larger numbers especially during summers and falls which corresponds to higher recorded rates of plague occurrence. But we cannot entirely rule out human body lice’s involvement.

Relevance Of this Research Today

Knowing more about how plagues spread is not just significant historically, but it has practical relevance for today as well since plagues still break out occasionally, particularly in parts of Africa, Asia, and Americas.

Fast treatment with antibiotics can effectively control it but constant monitoring is needed especially where plague infected rodent populations exist. Hygiene breaking down like seen during wars or refugee camps may possibly increase transmission risks via body lice so public health officials should factor both fleas and lice into their protocols for dealing with potential new outbreaks of plague.

Hurdles In Running Lice Based Plague Studies

Keeping a population of human body lice in labs presented major issues. As Hinnebusch explained, they are high maintenance creatures needing daily feeding on human blood which takes up a lot of resources. But a partnership with University of Massachusetts Amherst lab experienced at maintaining louse colonies helped make such studies achievable.

Why Studying Lice Can Be Historically and Medically Meaningful

Kritsky and his team’s findings shed new light on our grasp of the Black Death by acknowledging possible involvement of body lice’s in transmitting the plague. This defies the long-accepted theory that only rat fleas were liable which implies we may need to reconsider how other historic disease outbreaks might have occurred and stresses upon considering all potential vectors or carriers while constructing effective preventative and control strategies against diseases.

Final Takeaway

Rat fleas are widely accepted as being chiefly responsible for the Black Death’s proliferation, but human body lice’s’ part cannot be totally denied. New study indicates that lice’s may have been capable of more efficiently transmitting Yersinia Pestis than previously considered which adds new layers to our understanding about the spread of one of history’s deadliest plagues. It serves as a reminder to maintain vigilance against all plausible transmission vectors for preventing future pandemics.


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