Pig heart transplants have been confirmed to have a virus.

Researchers investigating the death of the first human recipient of a pig's heart have revealed that the organ had an animal virus

but they are unable to determine whether this was the cause of the man's death.

It was only two months after the landmark experimental transplant that 57-year-old David Bennett Sr. died in March. 

In the heart of a pig, scientists at the University of Maryland identified viral DNA, they said on Thursday

Porcine cytomegalovirus (PCV) was not found to be the source of any current infection.

Animal-to-human transplants, on the other hand, have raised concerns about the possibility of introducing patients to new strains of illness.

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