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Judge Paola Plaza speaks to reporters in Santiago, Chile, on Feb. 15, after receiving a report by international forensic experts regarding the cause of death of Chilean poet Pablo Neruda.Esteban Felix/The Associated Press

The Chilean poet Pablo Neruda died with toxic bacteria in his body, scientists have found, a result that is consistent with – though not proof of – allegations that the Nobel laureate and diplomat was poisoned soon after a military coup toppled Chile’s government in 1973.

After a detailed analysis, parallel teams working in Canada and Denmark found DNA belonging to Clostridium botulinum in a single molar and in bone fragments that were sampled in 2015 after the poet’s body was ordered exhumed.

The neurotoxin-producing species, which causes botulism, is one of the most dangerous pathogens known.

“We’re feeling very confident that it was present in his body when he died,” said Debi Poinar, a research associate with McMaster University’s Ancient DNA laboratory in Hamilton, who led the Canadian part of the investigation.

Researchers hope Pablo Neruda's bones hold answer to poet's death

Ms. Poinar was among the experts who presented their findings to a Chilean tribunal on Wednesday. Although the hearing was not open to the press, lawyers had leaked news earlier in the week that suggested forensic teams had verified that Mr. Neruda was poisoned.

“We made it clear that we could not say that,” Ms. Poinar said. She added that further investigations could help remove some of the remaining ambiguity around the poet’s death.

Born in 1904, Mr. Neruda was internationally celebrated for his literary works, including Twenty Love Poems and a Song of Despair, first published in 1924. A prominent left-wing intellectual and avowed communist, he served as Chile’s ambassador to France from 1970 to 1972 during the government of president Salvador Allende.

He died on Sept. 23, 1973, just 12 days after the U.S.-backed coup that swept Mr. Allende from power and hours after he returned home from a clinic where he suspected that he had been injected with something.

The suspicion that Mr. Neruda was the victim of a covert assassination is long-standing. It is bolstered by the fact that Clostridium botulinum is a known biological weapon that was employed by agents of general Augusto Pinochet, who ruled Chile following the coup until 1990. In 2021, five ex-officials of the regime were convicted of using the toxic bacteria to poison a group of political prisoners who were held in a Santiago jail in 1981.

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Research assistant in the department of anthropology at McMaster University in Hamilton looks at sliced bone fragment of poet Pablo Neruda in February, 2016.Glenn Lowson/The Globe and Mail

In 2017, the McMaster team helped to determine that Mr. Neruda did not die of prostate cancer, which has been listed as his official cause of death.

Together with their Danish counterparts, the team was then able to demonstrate the presence of Clostridium botulinum after collecting and reconstructing fragments of bacterial DNA from Mr. Neruda’s remains, in particular the interior of the tooth that they sampled.

In their investigation, researchers turned up the DNA of other bacteria, including those that cause tooth decay, and another species associated with a urinary-tract infection that the poet is known to have had. This added to the team’s confidence that they were sampling microbes that were present in Mr. Neruda’s blood when he died rather than those that may have shown up long after his burial.

“We think we’ve done a pretty good job of creating a picture of what the microbial life of his blood was at the time of death,” Ms. Poinar said.

But the result was not enough to make firm conclusions about the cause of Mr. Neruda’s death because, unlike some human pathogens, Clostridium botulinum can also live in soil.

To eliminate the possibility, the McMaster team then tested soil samples obtained from around the burial site. They were not able to find a match with the Clostridium botulinum present in Mr. Neruda’s body.

The team also undertook a more detailed exploration of the DNA they retrieved to see if they could identify the genes associated with the neurotoxin that is produced by the deadliest strains of the Clostridium botulinum. However, the team was only able to reconstruct about one-third of the bacterial genome that lacked most of the genes required to enable the toxin. This meant the result was not enough, on its own, to say that Mr. Neruda had been killed by the bacterium.

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In this October 21, 1971 file photo, Nobel Prize winning poet Pablo Neruda sits in Paris France.MICHEL LIPCHITZ/The Associated Press

“We got some really interesting scientific information on this thing, but it’s not definitive. It doesn’t tell us what happened,” said Charles Brenner, an expert panel member and forensic mathematician affiliated with the University of California Berkeley Human Rights Center.

Dr. Brenner added that the result was still a big step forward, considering that “up to now there was nothing but rumours.”

In their report, the McMaster team said that another avenue of investigation would be to sample the remains of those prisoners who were known to have died of Clostridium botulinum in 1981. If the bacteria that killed them were to match the one that was found in connection with Mr. Neruda, it would provide a definitive link to the Pinochet regime, since the chance of two genetically identical strains showing up under such circumstances would be astronomically small.

“It would be a slam dunk,” Ms. Poinar said.

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