Studies suggest the new mutations could cause the virus to be more deadly and spread more easily.

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However, there is no evidence that the mutations make it easier for the bug to cling to a persons upper lungs – a development that would raise concerns about spread among people.

Despite the new mutations, the threat to people from the virus remains low, Centre for Disease Control (CDC) officials have said.

The mutations, which have only been noted in the one hospitalised patient, may have occurred after the man got sick, the CDC added.

There is no evidence that the mutated virus spread to other people, mixed with other flu viruses, or developed the evade medicines and vaccines.

This type of flu, called Type A H5N1, was first identified as a threat to people during a 1997 outbreak in Hong Kong, when visitors to live poultry markets caught it.

Some 868 human H5N1 cases have been reported over the last two decades, just over half (456) have been fatal, according to the World Health Organisation.

There have been some reports of human-to-human transmission – but this is very rare.

The vast majority of infected people got it directly from birds.

Fears have been raised in recent months due to the “unprecedented” current outbreak among birds and mammals.

Experts worry the sheer scale of the current spread could give the virus more opportunities to mutate, which could enable H5N1 to better spread in humans.

Earlier this year, an 11-year-old girl from Cambodia died after catching the big from infected poultry.

Scientists are calling on the Government to create a new bird flu vaccine before the virus learns to more effectively jump to humans.

The new lab analysis looked at the virus found in the lungs of a 53-year-old man living in Chiles Antofagasta region.

He may of been infected through contact with sick or dead birds or infected sea lions, according to a WHO summary of the case.

The man was healthy and had not travelled recently. On March 13, he started getting a cough, sore throat and hoarseness, the WHO said.

His symptoms worsened and he eventually was sent to an intensive care unit and treated with antiviral medicines and antibiotics. He is still hospitalised and being monitored, CDC officials said.

Genetic testing this week revealed the two concerning mutations.

It comes just weeks after 40,000 poultry were culled in central Chile on Wednesday after the country detected its first case of bird flu.

Andrew Pekosz, a flu researcher at Johns Hopkins University, said he hadn’t seen the analysis of the virus found in the Chilean patient.

There are three or four kinds of mutations that would need to be seen in a H5N1 virus before that would really raise the alarm signal that something is happening of concern, he explained.