Genetic analysis of Medicis’ remains reveal Renaissance-era malaria strains - and closes book on a murder mystery

In 1562, Cardinal Giovanni de Medici, a scion of the dynastic family that dominated politics and banking in Tuscany during the Renaissance, died of malaria. Twenty-five years later, his older brother, Grand Duke Francesco de Medici, succumbed to the same disease.

In a new study, Yale researchers in collaboration with paleopathologists from the University of Pisa in Italy conducted a genetic analysis of the brothers’ skeletal remains in search of several Plasmodium species, the parasitic protozoa that cause malaria.

They found a novel strain of Plasmodium falciparum, the species that causes the deadliest form of human malaria, in the bones of Giovanni de Medici. The researchers also discovered molecular traces of P. falciparum and a second species, P. malariae, in the remains of Francesco de Medici.

The findings — which support an ongoing effort to track the spread and evolution of malaria in Central Italy during the Renaissance and beyond — provide insights into the genetic diversity of P. falciparum and the evolution of malaria species.

The results also offer scientific proof to dispel persistent speculation that Francesco de Medici was poisoned to death, researchers say.

“Our study is a great example of how we can use advanced ancient DNA laboratory methods to map the history of this deadly pathogen,” said senior author Serena Tucci, assistant professor of anthropology in the Yale’s Faculty of Arts and Sciences.

Their work doesn’t just help illuminate events from the past, added Adalgisa Caccone, a senior research scientist in Yale’s Department of Ecology & Evolutionary Biology and co-author of the study. “It also generated data that can inform current and future research on malaria, which remains a deadly disease that afflicts millions of people worldwide,” she said.

The study was published in the journal iScience. Alexander Ochoa, an associate research scientist in Yale’s Department of Ecology & Evolutionary Biology and Department of Anthropology, is the first author.

Malaria was endemic to Central Italy from the ancient period into the 20th century, when eradication campaigns eliminated the disease from the region. But in other parts of the world, the disease still poses a dangerous public health threat. In 2024, there were about 282 million malaria cases worldwide, causing 610,000 deaths, according to the World Health Organization.

For the new study, the researchers extracted DNA from four rib samples — three belonging to the grand duke and one belonging to the cardinal. The brothers are entombed in the Medici Chapels, mausoleums within the Basilica di San Lorenzo in Florence, Italy, where the principal members of the Medici family are buried.

The finding that Francesco de Medici had traces of two malarial species aligns with earlier analyses of samples from Belgium from the same historical period showing co-occurrences of malaria in individuals. However, Ochoa said, further genetic sequencing is needed to confirm that the two species were co-occurring in Central Italy during the 16th century.

The P. falciparum strain recovered from Giovanni de Medici includes two unique genetic mutations that likely derived from demographic expansion as the parasite spread across Europe, according to the study.

“The study of ancient DNA offers us an opportunity not only to diagnose malaria in the remains of individuals from the past, but it also offers us a window for understanding the evolution of malaria species, Plasmodium falciparum in this case, which can help scientists better understand how the pathogen adapts over time,” Ochoa said.

[The findings offer] a window for understanding the evolution of malaria species, which can help scientists better understand how pathogens adapt over time.

Alexander Ochoa

Cardinal Giovanni de Medici contracted malaria with his mother, Eleonora of Toledo, and younger brother, Garzia, during a 1562 trip to the Tuscan coast, where the marshes were known to be a breeding ground for malaria. All three endured recurring fevers that killed them over the course of a month. The cardinal was 19 years old.

In 1587, Francesco de Medici and his wife, Bianca Cappello, visited the Medici family’s villa in Poggio, which was located amid swampy rice fields where mosquitos thrived. The couple died on consecutive days after suffering intermittent fevers consistent with malaria. Their quick deaths spawned rumors that Francesco’s brother and rival, Cardinal Ferdinando de Medici, had them poisoned with arsenic.

Archival sources, including contemporary reports from court physicians, describe the symptoms the brothers suffered that are consistent with malaria, which was called “febbre terzana” by residents of Central Italy at the time. 

The reports also describe the treatments to which the stricken were subjected, including bloodletting, a common practice that likely did patients more harm than good.

Now we can say with scientific certainty that malaria, not poisoning, killed Grand Duke Francesco de Medici

Valentina Giuffra

Prior immunological analyses performed by the team of the University of Pisa had indicated that both Giovanni and Francesco carried P. falciparum. But, until now, no genetic assessment had been made on their skeletal remains to confirm those findings, the researchers said.

“At the time, both were diagnosed with symptoms, such as intermittent fevers, consistent with malaria,” said study co-author Valentina Giuffra, full professor of history of medicine at the University of Pisa. “This genetic analysis confirms the historical accounts as well as prior research. Now we can say with scientific certainty that malaria, not poisoning, killed Grand Duke Francesco de Medici.”

Other co-authors of the study are Samantha Miller and Patrick Reilly of the Yale Human Evolutionary Genomics Laboratory and Gino Fornaciari, Antonio Fornaciari, and Giulia Riccomi of the Department of Translational Research and New Technologies in Medicine and Surgery of the University of Pisa.