Ancient DNA analysis resolves 400-year-old Medici death mystery

A new study led by Yale University and the University of Pisa has utilised ancient DNA analysis to determine that Grand Duke Francesco I de’ Medici died of malaria rather than arsenic poisoning. The research, published in the journal iScience, identified genetic traces of Plasmodium falciparum and Plasmodium malariae in Francesco’s skeletal remains, resolving a 400-year-old mystery surrounding his 1587 death alongside his wife, Bianca Cappello. While some historians maintain that poisoning may have contributed to his demise, the authors argue the genetic evidence provides a definitive explanation for the illness.

The investigation centred on bone samples extracted from Francesco’s ribs and those of his brother, Cardinal Giovanni de’ Medici, who died 25 years earlier. Researchers found that Francesco suffered a double infection with two distinct malaria species, while Giovanni’s remains contained a previously unknown strain of Plasmodium falciparum. The study utilises ancient DNA analysis, which researchers argue is more definitive than previous paleo-immunological methods or toxicological investigations. The research was conducted on samples kept aside when Medici tombs were opened in 2004, as the technology was not sufficiently developed at that time.

Rumours of assassination persisted due to Francesco’s younger brother, Ferdinando, who stood to inherit the throne and had visited the couple shortly before they fell ill. Historical records from court physicians described symptoms consistent with malaria, including intermittent fever, and noted treatments such as bloodletting, which likely worsened the patients' conditions. Previous studies, including one in 2006, suggested arsenic poisoning based on toxicological investigations, while earlier paleo-immunological studies (since 2004) had hinted at malaria.

Valentina Giuffra, a professor of history of medicine at the University of Pisa and coauthor of the study, emphasised the superiority of DNA analysis over previous methods. She noted that while paleo-immunology attested to the presence of malaria, it was not resolutive, whereas ancient DNA offers a high degree of certainty by looking for direct genetic signatures of a disease. Giuffra stated that the DNA evidence solves the problem and the doubts surrounding the cause of death.

Despite the new findings, debate continues within the academic community. Donatella Lippi, a professor who supported the assassination hypothesis in 2006, argued that contracting malaria does not preclude poisoning. She cited historical records mentioning skin eruptions and swelling, symptoms she associates with acute arsenic poisoning. However, Giuffra countered that these findings were based on biological tissue from a different location, not the skeletal remains, and suggested Francesco’s interest in alchemy could explain the skin eruptions.

Other experts remain cautious about declaring the matter fully settled. David Caramelli, a professor of anthropology at the University of Florence, noted that while the study provides evidence consistent with malaria, it does not definitively rule out poison. He argued that the presence of pathogen DNA is not necessarily equivalent to demonstrating the cause of death and should be interpreted alongside historical and archaeological data. Nevertheless, he acknowledged the research as an important step forward for paleogenomics.

The study also contributes to understanding the evolution of malaria in Renaissance Central Italy. Alexander Ochoa, an associate research scientist at Yale and first author of the study, highlighted that the detection of different malaria species helps fill a historical gap regarding the disease's spread in the region. The findings underscore how technical advancements in genetic analysis can address longstanding historical questions, even if they cannot entirely eliminate speculation about concurrent poisoning.