The xenotransplant patient who made history by receiving a pig heart has died, about 40 days after his operation. David Bennett, a 57-year-old with serious heart failure, may have died of a pig virus, but doctors are still not sure what triggered his death.

The transplant team at the University of Maryland announced that they had found porcine cytomegalovirus in Mr Bennett’s body, even though the pigs were specially bred to avoid passing on porcine viruses.

Antonio Regalado, who broke the story in MIT Technology Review, noted that:

“Transferring pig viruses to humans has been a worry—some fear xenotransplantation could set off a pandemic if a virus were to adapt inside a patient’s body and then spread to doctors and nurses. The concern could be serious enough to require lifelong monitoring for patients.”

A German virologist told Regalado: “It’s a latent virus and hard to detect. But if you test the animal better, it will not happen. The virus can be detected and easily removed from pig populations, but unfortunately they didn’t use a good assay and didn’t detect the virus, and this was the reason. The donor pig was infected, and the virus was transmitted by the transplant.”

Doctors stressed that Mr Bennett was extremely unwell even before the operation, so the pig virus may have only been one of a number of factors in his death.

The death has revived ethical questions about the risky experiment. Bioethicist Arthur Caplan, of New York University, told Regalado that he had doubts about whether a man in Bennett’s precarious health could give informed consent.