Minutes for a homicide trial


French Black Death, by Aronski, licensed under CC Attribution Sharealike Unported 3.0 licence. Click image for source

The defendant:
FIRST NAME: Yersinia

LAST NAME: pestis

IDENTITY: Rod-like bacteria, pathogens responsible for plague

The allegation:
Mass murder: between 125-250 million deaths during the three major episodes of plague.

The evidence:
EXHIBIT A: Plague of Justinian from 541 to 767 AD.

The first episode began in the sixth century and is known as the Plague of Justinian, named after the Byzantine Emperor Justinian, who ruled at the time. Between 25 and 50 million lives were lost during this devastating outbreak, which spanned the globe from the East to Europe. As well as extreme economic and social consequences, the plague enabled new conquests, such as invasions of the weakened Persia and Bryzantium by the Islamic armies. Plague also enabled the conquest of Britain by the Saxons as invaders could just plough right through weakened defences.

EXHIBIT B: The Black Death, from 1347 to 1352

The second episode of plague decimated Europe in the Middle Ages, causing between 75 and 200 million deaths in five years. Termed the Black Death, it caused a social revolution, essentially leading to the end of feudalism and serfdom. Causing the death of the workforce, lack of labourers forced the lords to pay people to do the work formerly done for free by servants.

EXHIBIT C: The Modern Plague from 1855 to 1959

The latest savage attack by Y. pestis began in China and India in the late 19th century, before it spread to every  continent in the early 20th century. Modern Plague has caused the deaths of 10 million people. It is still active in some regions in Asia, Africa and North and South America. Doctor Alexandre Yersin highlighted and described the causative agent of plague, our main suspect, Yersinia pestis, in Hong Kong in 1894. Y. pestis (shown below) is thus named after Dr Yestin – oh, the perks of working in science!…


Yersinia Pestis. Title: PHIL_1918_lores_Floureszenz_Yersinia.jpg, image in public domain. Transferred to Commons by Mattias_M in October 2010. Click image for source

The bacterium Yersinia pestis infects fleas and lice. These pesky buggers bite people and thereby transmit the microbe. Rodents are key carriers – they provide a nice, warm bloody home for fleas infected by Y. pestis. When rodents live near humans (and they’re never far away from us) it increases the likelihood that humans will catch Y. pestis as they are bitten by the fleas. Rats! In this way rodents are key in promoting the spread of disease.


False colors Scanning Electron Micrograph of a Flea. Attribution: Centers for Disease Control and Prevention, by Janice Hanley Carr. CC image in the public domain.

Once in the body, Yersinia travels from its entry wound to the nearest lymph node. The node begins to swell and fester (yum!) – this marks the first symptom of the so-called bubonic plague. Bacteria then invade the rest of the body, causing a rapidly fatal septicemia (blood poisoning).

Similarly, Yersinia pestis can invade the lungs and cause pneumonia. Patients are then very contagious; transmission of Y. pestis occurs when the victim coughs up infected sputum, which is then inhaled by another person. Pneumonic plague can arise, bypassing the bubonic stage.

As reported previously, Yersinia pestis was identified as a pathogen causing the Modern Plague. For the other two killer episodes, it was necessary to determine how to find traces of bacteria on human remains dating from hundreds of years ago.

The first step for paleomicrobiologists (researchers studying the traces of microbes on archaeological remains) is to find the remains of people who died of the plague. In epidemics, during which there are hundreds of deaths each day, it is impossible to properly bury the dead; they are often piled up in mass graves (plague pits). Human remains found today in these graves are dated with carbon-14) and so it is possible to accurately estimate the date of their death. If this date corresponds to the periods of the Plague of Justinian or the Black Death, it is likely that these people died of plague.

Once scientists identify the victims of the plague, they then look at their teeth. Examination of medieval dental work?! – the scientists are particularly interested in the dental pulp (internal part of a tooth). As Yersinia moves throughout the body in the bloodstream, traces of its passage can remain in  teeth, which are protected by tooth enamel for hundreds of years. DNA contained in the pulp can thus be extracted from the teeth. The researchers then use what are called primers to perform a polymerase chain reaction, or PCR. Primers are small pieces of DNA which essentially recognize Yersinia pestis DNA and reveal its presence in the pulp.

With new sequencing technologies and DNA analysis software, scientists identified Yersinia pestis in samples dating from episodes of the Plague of Justinian and the Black Plague, leaving no room for doubt – it was Y. pestis whodunit!

Present on most continents, Yersinia pestis still exists in isolated homes mainly in Africa and Asia. Although the risk of transmission is lower thanks to improved hygiene, danger is still present. Plague remains a contagious disease with a high mortality rate if untreated.

Yersinia pestis was repeatedly used as a biological weapon through the centuries until the Cold War. It is considered a significant risk to the people’s security because of its potential use by terrorists in biological warfare. Antibiotics can cure the plague if the patient is rapidly treated, but scientists warn us that Yersinia pestis can also be genetically engineered to be resistant to these antibiotics.

Update – Last year the Centers for Disease Control and Prevention in the US reported the first known incidence of plague transmission from a dog to a human. Uh oh…

VERDICT: Yersinia pestis is deemed GUILTY and is refused the right to appeal.

This article is by Virginie Barrere, bilingual curator of the blog www.parasitesetcie.com, depicted below in glorious Technicolor (?).


For those interested, the review by Ligon, B.L. (2006) further details use of plague as a bioweapon: Plague: a review of its history and potential as a biological weapon. Semin Pediatr Infect Dis. 17:161-70.

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    • The author: Yes, I agree, I apologize for the scary side of the article, but when I found out that it can be done, I figured I should let people know. You can find the information on this publication: Plague: A Review of its History and Potential as a Biological Weapon by B. Lee Ligon, and published in 2006. However, Plague is not that good to be transmitted from a person to another. But still, yes, it is scary…

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