A 'healthy' teenager is in critical condition after catching bird flu in Canada.
And in a potentially alarming development, health officials say it's not clear how they became infected.
The patient, who has not been identified, is currently being treated in a children's hospital in British Columbia.
'This was a healthy teenager prior to this, so no underlying conditions,' said provincial health officer Bonnie Henry.
'It just reminds us that in young people this is a virus that can progress and cause quite severe illness and the deterioration that I mentioned was quite rapid.'
The teen began suffering a fever, cough and 'pink eye' on November 2 and was admitted to hospital on November 8.
They have deteriorated since and are now suffering from severe lung damage making it hard to get oxygen around the body.
Health officials are still identifying the exact strain, but the patient is assumed to have H5N1, the virus that has infected dozens of Americans this year.
PINK EYE: The H5N1 virus causes eye inflammation, as seen in a dairy farmer in Texas who caught bird flu earlier this year
The Canadian teen - who is Canada's first bird flu victim in the latest outbreak - had no farm exposure but had been exposed to dogs, cats and reptiles.
But no infection source had been identified. 'That is absolutely an ongoing investigation,' said Henry.
The World Health Organization says H5N1's risk to humans is low because there is no evidence of human to human transmission.
In Canada, British Columbia has identified at least 26 affected premises across the province and numerous wild birds have tested positive.
Canada has had no cases reported in dairy cattle and no evidence of bird flu in samples of milk.
But disease experts have warned that as the virus circulates, the chance of evolving increases, which could lead to a pandemic.
A pig on an Oregon farm tested positive for H5N1 for the first time in the US last week which caused alarm because pigs have been a source of prior human pandemics.
Bird flu has infected nearly 450 dairy farms in 15 states since March, according to USDA data.