The blood of the revolutionary Marat unveils its agony 200 years later

Last year, a team of scientists walked into the National Library of France in search of a bloody newspaper page. In it they hoped to find the answer to an enigma that has haunted the minds of doctors and scientists for decades: what horrible skin disease forced the revolutionary Jacobin Jean-Paul Marat to live inside a bath of calming waters where, in July 1793, he was stabbed to death by a woman named Charlotte Corday?

On the day of his death, Marat read The friend of the people, the newspaper he himself wrote and directed. She had given Corday an interview—a covert conservative—and at that time listed for her the list of her worst enemies. The woman stabbed him by surprise under his right collarbone, a fatal wound that severed his aorta and punctured his lung. The margins of the paper were covered in blood,

Marat's sister kept the papers, which since then passed through the hand of several private collectors until they were donated to the National Library, in Paris. The researchers passed a cotton-tipped swab both through the bloodied part and across another corner without stains. The samples were sent to the office of Carles Lalueza-Fox, a geneticist at the Institute of Evolutionary Biology in Barcelona and one of the world's leading experts in retrieving ancient DNA.

'Death of Marat', by David.

Marat was one of the fiercest and most celebrated revolutionary politicians and journalists. He was also a physician and published several books on science. He himself recounted that the skin disease started in his groins and then spread throughout his body causing terrible itching and painful ulcers that he could only relieve in the bathtub, where he arranged a table as a desk to continue filling the pages of your newspaper. The revolutionary thought he had contracted his evil in the sewers of Paris, where he had to take refuge from his political enemies in full reign of revolutionary terror,

Corday was put to justice a few days after the murder and Marat became a martyr. Jacobin painter Jacques-Louis David immortalized him in a masterpiece considered the secular piety of the French Revolution. His body was buried with honors in the Pantheon, but in 1795, after the revolutionary furore, his body was removed from there and since then his remains have been in an unknown location. The dried blood in The friend of the people is "probably" the only biological material left of it, explains Lalueza-Fox.

After a year of work, your team has just published the genetic analysis results to the public repository Biorxiv. They've recovered over 500 million DNA sequences. 72 million are human and most belong to Marat. This is the oldest DNA that has been recovered from a paper document, the study highlights. Researchers have managed to reconstruct their mitochondrial genome and part of the nuclear tree and have confirmed details of their family tree, such as the provenance of their parents: a French man and a Sardinian,

However, the most interesting thing is in the non-human sequences. Researchers have found DNA from viruses, bacteria and fungi in the blood. It is very likely that such an old sample that passed through so many hands will have pollution both at the time and the present day. To minimize it, researchers have compared the DNA in the stained corner to a clean one on the same page

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No trace has been found, no trace of syphilis, leprosy, scrofula caused by tuberculosis bacteria, thrush due to diabetes or scabies, the diseases attributed to it by different researchers since Marat's death. According to the analysis of the Spanish team it is impossible to know which disease was the culprit, but they do point to the main suspect: Malassezia restricta, a fungus that causes seborrheic dermatitis, another of Marat's hypothetical ailments.

"This fungus inhabits only human skin, it is strange to find it in the ancient documents and its DNA tells us that it is a not current variant, but can be from about 200 years ago", explains Lalueza-Fox. "There were no treatments for this infection at the time, so if i had been suffering it for three years, it was possible that the fungus had reached the blood causing immunosuppression and sepsis. If so, Marat would have died in a few weeks if they hadn't killed," he highlights

The team has found two other microbes whose DNA also indicates that they may be from the time: Staphylococcus aureus, which causes eczema, and acne bacteria. These secondary infections could have contributed to the itching that pursued the revolutionary to death,

In a case of forensic genetics with samples from 226 years ago, it makes sense for there to be loose ends. Antonio Alonso, director of the Institute of Forensic Sciences, explains that "the main problem is that there is no comparative genetic analysis of relatives to show that it is a sample of Marat's blood". "On the other hand, the swab sampling method is very inefficient compared to clipping the stain to extract DNA, but it is logical that this has been avoided to keep the newspaper intact."

"This case is well known among dermatologists, explained in the textbooks", explains Raúl de Lucas, head of pediatric dermatology at La Paz hospital, in Madrid. "Because of the symptoms and its severity we believe it was a skin lymphoma [a rare white blood cell cancer]. The fungus that has been found should not be able to spread throughout the body or end up killing anyone, even at that time, unless Marat has had an immunodeficiency, which is possible," he says,

There's a way to continue the investigation: locate another of the bloody papers that Marat had in his bathtub the day he was killed. "We know that it exists and that its owner is an English lord, but we have not yet contacted him," explains Lalueza.