Learning from Ancient DNA: What Plagues History?
S Krishnaswamy
FOR centuries, the story of the Plague of Justinian, history's first recorded plague pandemic, was woven solely from ancient texts describing a mysterious and devastating sickness that helped weaken an empire. Now, as reported in the journal "Genes" in the article Genetic Evidence of Yersinia pestis from the First Pandemic – a global team of researchers from USA, Australia and India used stringent ancient DNA protocols to extract highly degraded ancient DNA in dental pulp and human teeth. These were taken from remains in a mass grave found in an archaeological site dated approximately 550-660 CE (current era) in Jerash (the ancient city of Gerasa) in Jordan, near Amman. Subsequent proteomic and genomic analyses confirmed that the bacterium Yersinia pestis was the cause of the first Plague pandemic. A companion study in the journal "Pathogens" in the article Ancient Origins and Global Diversity of Plague: Genomic Evidence for Deep Eurasian Reservoirs and Recurrent Emergence – led by the same international team, placed this discovery into a wider evolutionary context, using phylogenetic analysis of hundreds of ancient and modern genomes of Yersinia pestis to reveal a startling pattern: plague has not arisen from a single source but has repeatedly and independently emerged from deep Eurasian animal reservoirs across millennia. Together, these findings increase our understanding of pandemics, highlighting a sobering truth – the complex interplay between human society and ancient pathogens is not a relic of the past but a recurring feature of our world.
HISTORY’S UNWANTED HITCHHIKER
The highly pathogenic bacterium that causes plague was identified in 1894 by Alexandre Yersin in Hong Kong and was named as Yersinia pestis. When the bacterium infects fleas, it starts its intricate life cycle. The bacteria multiply in the flea's gut. This leads to obstruction of the gut, and the flea gets starved. The flea then jumps to a host, which could be a human or another rodent, and in its urgent attempt to feed, regurgitates the bacteria into the bite wound. Rodents are the main reservoir in this cycle. Humans become unintended hosts due to bites by infected fleas. Critically, these fleas could travel vast distances undetected, hidden within bales of cloth, grain sacks, and other goods transported along trade routes, allowing the stealthy transit of the pathogen between cities and continents.
There are three main ways the illness presents itself. The most prevalent, bubonic plague, which is spread by flea bites and results in painful, enlarged lymph nodes called buboes, kills 30 to 60 per cent of untreated cases. In septicemic plague, bacteria enter the bloodstream, causing gangrene and rapid organ failure. The deadliest and only airborne form of plague, pneumonic plague, develops from the other forms or is transmitted directly between people through droplets, causing respiratory collapse. If treatment is not received within 24 hours, it is almost always fatal.
New research suggests that human ectoparasites (parasites that live on the outer surface, eg., skin of the host), such as lice, can also be involved in transmission in addition to the flea-rodent system. This was a major factor in outbreaks, as body lice can be carried by clothing and bedding. This was particularly important during the winter months when flea activity decreased. It has been hypothesised by some studies that natural immunity to Yersinia pestis is present in carriers of recessive familial Mediterranean fever (FMF) mutations. There is a high frequency of FMF mutations in populations around the Mediterranean (e.g., Turks, Armenians, Sephardic Jews, Arabs, and non-Ashkenazi Jews).
Researchers reported in 2019 in the journal "Cell" the most ancient case of Yersinia pestis, dating back 4,900 years ago. Their finding was based on ancient DNA analysis of archaeological remains from two individuals at a site in Sweden. This ancient strain is the oldest ever discovered and sits at the base of the family tree for all known modern and ancient Y. pestis strains. Their further analyses showed that many descendants of Y. pestis branched and expanded throughout Eurasia when the Neolithic populations in Europe were diminishing, between 6,000 and 5,000 BP (BP refers to year before present as distinct from the more common BCE and CE which measures Before Commons Era and Commons Era. It is a time scale used mainly in archaeology).
Analysis of the human genomes and the archaeological context showed that the emergence and spread were more likely due to expanding trade networks, population growth and lifestyles and not because of massive migrations. Their results corroborate those of other prior ancient DNA studies, proposing the existence of a prehistoric plague pandemic in Europe, which has also been linked to the decrease of Neolithic populations.
Three major plague pandemics have been recorded in human written history. During the Plague of Justinian (541-549 CE with recurrences into the 8th century), an estimated 25-50 million people from the Byzantine Empire to Ireland were killed. The first pandemic weakened the Byzantine empire and altered the course of western civilisation. Then followed what has been called Black Death (1347-1352 the deadliest wave of a second pandemic that reappeared sporadically until the 18th century). This second plague pandemic wiped out up to half of Europe's population – around 25 to 50 million people – within just five years, with global estimates of 75 to 200 million. It triggered widespread social upheaval and probably accelerated the collapse of feudalism. The Third Pandemic (1855-1959), a relatively slow mover, originated in China's Yunnan province. It spread globally via steamships and killed over 15 million people. In India alone, 12 million deaths occurred. British India became the epicentre, with Bombay and Punjab provinces hardest hit. In 1907, a single year, plague killed 1.2 million people in India.
LEARNING FROM PANDEMICS
The effect of plague went far beyond death. It collapsed economies, disrupted markets, and increased social disparities. The Plague of Justinian undermined the Byzantine state and contributed to long-term decline. The Black Death created shortages of labour that favoured peasants who could demand higher wages and undermined feudal hierarchies, accelerating Europe's transition out of feudalism. In colonial India, the epicentre of the Third Pandemic, British authorities adopted harsh and frequently coercive strategies – mass fumigation, forced evacuations, isolation in camps, and building inspections – that generated public resistance and exposed tensions between imperial authority and local communities. Pandemics lay bare the vulnerabilities of society: economic disruption and the tension between individual freedoms and the imperatives of public health. When the Black Death was happening, Jews were accused of causing the bubonic plague, maybe because they bore Familial Mediterranean Fever (FMF) mutations and were dying at lower rates than Christians. Jews were not the only ones who had this mutations, it was also shared with Turkish and Armenians. Accusing minorities of causing epidemics resounds throughout history and was also seen in India, perhaps for equally baseless reasons, during the recent coronavirus pandemic.
Pandemics, from the point of view of historical materialism, are never merely natural disasters but social phenomena that brutally expose the contradictions of the economic order. In the throes of crisis, the ideological veil is torn away, revealing the stark class divisions that structure our society. Pandemics and epidemics can be traced to a system that prioritises profit over human welfare. These force the serfs in a feudal system or the working class in a capitalist economy into conditions that breed infectious disease, while the aristocracy in a feudal system or the bourgeoisie in a capitalist economy retreat to safety. It can be called "social murder", a term that Engels uses in his writing in 1845, "Condition of the Working Class in England", to describe the unhealthy, crowded living conditions that workers were forced to be in for survival.
Yet, as Marx noted in "Capital", these same crises force the ruling class to implement reforms – not out of benevolence, but to preserve the health of the workforce, the very source of their profit. This is the fundamental contradiction: feudalism then or capitalism now creates the conditions for disaster and is then forced to mitigate them to ensure its own survival. Also, as the history of the plague demonstrated, as did the Covid-19 epidemic, germs transcend social boundaries. Even if the poor suffer a higher mortality, the rich are not spared either. Ultimately, a pandemic illuminates what is truly essential: the brutal inequities in healthcare, showcasing the conflict between public good and private profit. In doing so, it doesn't create new class struggles but sharpens existing ones, accelerates social change and reveals the urgent need to build a society organised not around capital and human greed, but around human need.
