Four US swans die from bird flu virus

Four swans found dead in Massachusetts had the bird flu virus, authorities said Wednesday, stressing that the strain was not dangerous to humans.

"Four of the swans were tested positive of H1 avian flu," a spokesman for the state's fisheries and wildlife department said. "It's a low pathogenic form. This form of avian flu is not harmful for humans."

The strain is commonly carried by birds, he added.

The most dangerous form of avian influenza is the H5N1 virus, which has infected about 600 people since appearing in 2003, killing one in two.

Outbreaks of H5N1 have been met with mass slaughter of at-risk livestock.