Girl in Australia, 2, struck with H5N1 bird flu — WHO

"This is the first confirmed human infection caused by avian influenza A(H5N1) virus detected and reported by Australia," the WHO said in a statement.

"Although the source of exposure to the virus in this case is currently unknown, the exposure likely occurred in India" where the girl had travelled, and where this group of "viruses has been detected in birds in the past", the UN health agency added.

The WHO assesses the current risk to the general population posed by the virus as low.

The girl had travelled to Kolkata from February 12 to 29. She did not have any known exposure to sick people or animals while in the city.

The girl returned to Australia on March 1 and was admitted to a hospital in the southeastern Victoria state the following day.

On March 4 she was transferred to an intensive care unit in the state capital Melbourne for one week, due to worsening symptoms. She left hospital after two and a half weeks.

The girl tested positive for influenza A while in hospital, and the samples were sent on in April for deeper characterisation.

"Virus genetic sequence obtained from the samples confirmed the subtype A(H5N1)... which circulates in southeast Asia and has been detected in previous human infections and in poultry," the WHO said.

The girl is reported to be well while no relatives in either Australia or India have developed symptoms.

The Indian authorities have been notified and have started an epidemiological investigation, the agency said.