Like a zombie in a horror movie, the coronavirus can persist in the bodies of infected patients long after death, even spreading to others, according to two surprising studies.
The risk of contagion is mainly for those who handle dead bodies, such as pathologists, forensics and healthcare workers, and in settings such as hospitals and nursing homes, where many deaths can occur.
While the transmission of dead bodies is not likely to be a major factor in the pandemic, grieving family members should exercise caution, experts said.
“In some countries, people who have died of Covid-19 are left unattended or returned to their homes,” said Hisako Saitoh, a researcher at Chiba University in Japan who published two recent studies on the phenomenon.
“Therefore, I believe it is knowledge that the general public should know,” he wrote in an email.
Several studies have found traces of infectious virus in cadavers up to 17 days after death. Dr. Saitoh and his colleagues went further, showing that dead bodies can carry significant amounts of infectious virus and that dead hamsters can transmit it to living cagemates.
The research has not yet been vetted for publication in a scientific journal, but outside experts said the studies were well done and the results convincing.
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The risk of a live patient spreading the coronavirus is far greater than the potential transmission of corpses, said Dr. Saitoh and other scientists pointed out.
If corpse infection accounted for a large number of cases, “we would have noticed, right?” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases.
Still, “if there’s an infectious virus, there’s always a risk of transmission,” he continued. “I don’t think it’s something that gets addressed often.”
In the United States, bodies are usually embalmed or cremated shortly after death. But in the Netherlands, where Dr. Munster grew up, as in many parts of the world, family members can wash and dress the bodies.
In July 2020, the Japanese government urged grieving family members to keep their distance from the corpses and refrain from touching or even seeing them. Officials also recommend sealing the corpses in waterproof bags and burning them within 24 hours.
The guidelines were revised in May 2022 to allow relatives to see loved ones who died of Covid, but “in an appropriately infection-controlled hospital room”.
These guidelines partly prompted Dr. Saitoh to explore what happens to the virus in the body after death.
He and his colleagues looked at samples from the noses and lungs of 11 people who had died of Covid. The researchers found that large amounts of virus persisted in six of the 11 cadavers, even 13 days after death.
“It was surprising that infectious titers were maintained at the same high levels as in clinical patients.” Saitoh wrote. “Most surprising, however, were the results of the animal experiments.”
In these experiments, he and his colleagues found that hamsters that died within days of being infected with the coronavirus could transmit it to other animals. Also in people, contagion is more likely when a patient dies soon after infection, when levels of the virus in the body are very high, the researchers said.
The team found more virus in the lungs of human cadavers than in the upper respiratory tract. This suggests that those performing autopsies should take special care when handling lungs, experts said. Dr. Saitoh pointed to a study from Thailand that described a medical examiner who appeared to have been infected on the job.
Gases that build up after death can be expelled through any orifice in the body, including the mouth, and can carry infectious viruses, the researchers said. Embalming or practicing so-called “angel care,” a Japanese ritual in which the mouth, nose, ears and anus are covered with cotton pads, prevented transmission, they found.
Contagious corpses are not without precedent. Most famously, funeral and burial practices have triggered large outbreaks of the Ebola virus in Africa.
But the coronavirus is very different, noted Angela Rasmussen, a research scientist at the Vaccine and Infectious Diseases Organization at the University of Saskatchewan in Canada.
Up to 70 percent of those infected with Ebola die, compared to about 3 percent of those diagnosed with Covid-19. And the Ebola virus floods all parts of the body, so the risk of transmission, even after death, is much greater than what is theoretically possible with the coronavirus.
“With Ebola, it’s clearly direct contact with body fluids, because there are high titers of Ebola pretty much everywhere in someone who has died of Ebola.” Rasmussen said.
She was initially skeptical that the coronavirus could spread from dead bodies, but found the new studies convincing.
“Most people probably still have to worry much more about getting Covid from their living neighbors than those who have recently died,” he said.
But “they should be very cautious about physical contact with the remains of their loved ones,” he added.