The World Health Organization has revealed the deadly bird flu virus which appeared as a cluster in an Indonesian family had mutated but the change does not increase the threat of a pandemic.

It seems an investigation has shown that the H5N1 mutation occurred in a boy aged 10 in a village in North Sumatra.

The initial source is thought to have been a woman infected by poultry who passed it on to the boy and five other blood relatives.

According to a report the boy is thought to have infected his father, whose test samples showed the same mutation.

Only one infected family member survived.

At that point say experts for the U.S. Centers for Disease Control and Prevention (CDC) the virus stopped dead.

The CDC says it is to be expected that viruses will change slightly and there is no reason for this mutation to raise alarm because the H5N1 affected blood relatives only and not spouses or other people in the village.

Meanwhile four people from a village in Azerbaijan, have died after catching avian flu from infected swans.

They are believed to have caught the lethal H5N1 virus earlier this year when they plucked the feathers from dead birds to sell for pillows.

Three other people were also infected by the swans but did not survive.

Experts from the Robert Koch Institute in Berlin, who made the discovery, say this is possibly the first transmission from a wild bird, which has been reported.

Almost all of the 220 other confirmed human cases of bird flu, including 130 deaths, have been linked to infected domestic poultry which is generally thought to be the major source of infection and many believe migratory birds are being unfairly portrayed solely as the carriers of the deadly virus.

The cluster was first reported in March in the Salyan district of Azerbaijan, where six of the seven cases all aged between 10 and 20, were from the same family.

Initially relatives denied any contact as the hunting and trading of wild birds is illegal; they eventually admitted that the victims had plucked the feathers from dead swans from a large number of the birds that died in February.

The surveillance of migratory birds in future is likely to be intensified and targeted on specific species of ducks, geese and swans than it was previously.

But experts insist picking up the virus from a dead bird is very difficult and extremely close contact is necessary.

The advice from scientific advisers remains the same, if you see a dead bird, don’t pick it up.