'Severely ill' man discovered to have 'unpredictable' virus that's never been seen before in humans

What is believed to be the world's first ever animal-to-human transmission of the H5N5 virus has taken place in Washington, with the infected man said to be 'severely ill'.

This strain of avian influenza, more commonly called bird flu, had previously only been detected in animals. But a man from Grays Harbor in Washington State was diagnosed with the infection after being admitted to hospital with a high fever, respiratory problems, and confusion.

After confirming the infection on November 14, health officials said the patient would remain in hospital as they are an older person with 'underlying health conditions'.

The man is understood to have kept a 'mixed backyard flock of domestic poultry' at his home, which had 'exposure to wild birds,' likely causing the H5N5 infection which caused him to fall ill at the start of this month.

Bird keepers are being urged to keep an eye on their animals (Jay L Clendenin/Getty Images)

Washington State Department of Health explained to residents: "On rare occasions, avian influenza viruses can infect people and make them sick. Most cases have occurred in people who were exposed to sick or infected animals."

The risk of bird flu spread increases significantly during the fall and winter months, with more wild birds migrating south and shedding the virus among domestic poultry populations.

Contact tracing is being rolled out in Washington to track down anyone who might have come into contact with the infected man.

"To ensure that human-to-human spread is not occurring, public health officials are contacting anyone who has been in close contact with the patient to monitor for symptoms and provide testing and treatment as needed," state health officials said.

However, despite this first-ever animal-to-human transmission of the H5N5 strain, the Center for Disease Control (CDC) continues to view the wider risk of avian influenza to the general population as low.

Poultry and cattle workers make up the majority of bird flu infections (Lokman Vural Elibol /Anadolu via Getty Images)

Other strains of bird flu have previously infected humans, with H5N1 and H7N9 variations identified in people, largely spreading from poultry to farm workers - there have been no human-to-human transmissions of this virus.

The H5N1 strain killed an older man in Louisiana in January, with a further 71 cases currently identified across the country by the CDC. 41 of these cases came from cattle workers, while 24 came from poultry workers.

Anyone in Washington state who keeps birds is being advised to monitor their health closely and report any sick or dead birds Washington State Department of Agriculture (WSDA), which can be notified online.

Citizens are also being urged to avoid touching any dead or sick wildlife they might notice while outside, with an additional warning to keep any pets away from deceased birds to help prevent the virus' spread.

People are also being warned to avoid unpasteurized milk and cheese, as well as raw or undercooked meats, to prevent any further spread of avian influenza.