Researchers Identify Bacterium Linked to First Recorded Pandemic
For the first time, scientists have found direct genomic evidence of the bacterium responsible for the Plague of Justinian—the earliest known pandemic—originating from the Eastern Mediterranean. This area had been described as the outbreak’s starting point almost 1,500 years ago.
This breakthrough, spearheaded by a diverse team from the University of South Florida, Florida Atlantic University, and collaborators from India and Australia, pinpointed Yersinia pestis, the pathogen behind the plague, in a mass grave located in the ancient city of Jerash, Jordan, close to the pandemic’s epicenter. This discovery firmly connects the germ to the Justinian Plague (AD 541–750), resolving a long-standing historical enigma.
Historians have long debated the cause of this catastrophic event that resulted in millions of deaths, restructured the Byzantine Empire, and shifted the trajectory of Western civilization. Although there was circumstantial evidence, hard proof of the bacteria remained elusive—a key piece missing from the narrative of pandemics.
Two new studies, recently published by USF and FAU, provide significant insights into this critical juncture in human history. The findings, shared in the journal Genes, also highlight the ongoing relevance of plague today; though infrequent, Y. pestis continues to circulate globally. For instance, in July, a person in northern Arizona died from pneumonic plague, the most lethal type of Y. pestis infection, marking the first reported death in the U.S. since 2007. Just last week, another individual tested positive for the disease in California.
“This discovery gives definitive proof of Y. pestis at the heart of the Plague of Justinian,” commented Rays H. Y. Jiang, Ph.D., the lead researcher on the studies. “For ages, we’ve depended on historical records describing a horrendous disease but lacked tangible biological evidence. Our results fill in that gap, providing a direct genetic perspective on how this pandemic unfolded in the empire’s core.”
The plague was first identified in Pelusium (modern-day Tell el-Farama) in Egypt before it spread throughout the Eastern Roman Empire. While Y. pestis was previously discovered in western Europe, no evidence had surfaced within the empire, particularly close to the epicenter of the pandemic.
“Utilizing advanced ancient DNA techniques, we successfully extracted and sequenced genetic material from eight human teeth found in burial chambers beneath the Roman hippodrome in Jerash, just 200 miles from ancient Pelusium,” explained Greg O’Corry-Crowe, Ph.D., a co-author and research professor at FAU. The arena had been used as a mass grave during the mid-sixth to early seventh centuries when historical documents describe a sudden surge in mortality.
Genomic analyses revealed that these plague victims carried nearly identical strains of Y. pestis, establishing for the first time that the bacterium existed within the Byzantine Empire between AD 550-660. This genetic uniformity implies a swift, devastating outbreak consistent with historical accounts of widespread death.
“The Jerash site offers a unique insight into how ancient societies handled public health crises,” Jiang continued. “Jerash was a pivotal city in the Eastern Roman Empire, known for its trade and impressive architecture. The fact that a venue once meant for entertainment turned into a mass burial ground in such dire times indicates how urban centers were likely overwhelmed.”
A related study also published in Pathogens by USF and FAU places Jerash’s discoveries within a broader evolutionary framework. Researchers analyzed hundreds of ancient and modern Y. pestis genomes, including those from Jerash, showing that the bacteria had circulated among human populations for millennia before the outbreak associated with Justinian.
The team also uncovered that later plague pandemics, like the Black Death in the 14th century and more recent cases, did not derive from a single strain. Instead, they independently emerged from long-standing animal reservoirs and appeared in waves across different regions and times. This pattern contrasts sharply with the COVID-19 pandemic, which originated from a single spillover event and spread largely through human-to-human transmission.
These findings reshape how we comprehend pandemics’ emergence, recurrence, and spread, highlighting that they are not isolated historical disasters but rather recurring biological events driven by human interaction, movement, and environmental changes—concepts still relevant in today’s context.
“It’s both scientifically compelling and personally meaningful. This work allowed us to explore human history through ancient DNA while navigating our own global pandemic,” remarked O’Corry-Crowe.
Jiang added, “We’ve been grappling with the plague for many centuries, and it still poses a threat. It evolves continuously, and our containment efforts don’t eliminate it entirely. Caution is necessary, yet the risk remains persistent.”
Building upon this monumental finding, the research team is now broadening its studies to Venice, Italy, specifically examining the Lazaretto Vecchio, a prominent site for plague burials. More than 1,200 samples from this mass grave dating back to the Black Death are now held at USF, presenting an extraordinary chance to investigate early public health responses, how they intertwined with the evolution of pathogens, and the impacts on urban environments.
