A Hong Kong laboratory officially recognized by the World Health Organisation (WHO) has confirmed the latest four cases of bird flu infection in humans in Indonesia.

Two of these have died which brings the death toll there to 35.

The WHO has requested that drug manufacturer Roche be prepared to supply the anti-bird flu drug Tamiflu to Indonesia should it be needed.

The drug company has sent 9,500 treatment doses of Tamiflu and protective equipment to Indonesia as a precautionary measure.

It is apparently standard for the WHO to guarantee drugs are ready for shipment when a cluster of infections occurs as in Indonesia.

Within two weeks when health authorities are assured the human transmission is only within the family of eight, the drugs will be returned.

Europe and USA have stockpiled an emergency supply of 3 million Tamiflu doses to combat human bird flu outbreaks in any part of the world where human transmission may be evolving.

The latest deaths include a 10-year-old girl from Bandung who is suspected of contracting the virus from sick birds and an 18-year-old man, a shuttlecock maker from Surabaya who is thought to have caught the virus from the bird feathers used to make the sports equipment.

The other two infections in a 39-year-old person from Jakarta, and a 43-year-old person from Jakarta are also thought to have come from sick birds.

Eight members of one family have already died of bird flu, seven confirmed and one more than likely who died and was buried before samples could be taken.

Scientists say tests indicate that the virus samples show no changes or traits which would make it able to infect humans more efficiently.

In order for a human pandemic to begin the H5N1 bird flu virus strain must mutate.

It appears that an H5N1 infected person can only at present infect another human when continuous, close physical contact exists.

The eight family members who died from the virus slept together in a small room and transmitted the virus to each other.

Inspectors have thoroughly searched the area where the family lived for signs of sick birds and have not found any.

It is however suspected the source was a sick bird.

Critics say Indonesian authorities are slow to respond to reports of infections and it is possible that by the time experts arrive sick chickens have been disposed of and the area cleaned.

The Indonesian cluster is the largest found so far but there have been others and researchers believe only blood relatives become infected in a cluster.

This theory opens up the possibility that there is a genetic susceptibility and could explain why there are hardly any reports of nurses and other health care professionals catching bird flu from sick patients despite the close, physical contact that occurs.

Tamiflu is an antiviral and not a vaccine but has been found to be effective if given to an infected patient in the early stages of the infection.