Louisiana chiefs have confirmed the first US fatality linked to the deadly H5N1 strain. The victim, a man over 65 with pre-existing health issues, succumbed to the virus after being rushed to for urgent treatment.

It's believed he caught the lethal bug from a mix of domestic backyard and wild fowl. Despite an extensive probe by the Louisiana Department of Health (LDH), no further infections or human-to-human spread have been detected.

This case remains the sole instance of H5N1 in both the state and across the country. LDH has sought to calm fears, emphasising that the risk to the public is still minimal, although those in close contact with birds or farm animals might face greater danger.

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Last month, the US Centers for Disease Control and Prevention disclosed that the virus had mutated within the Louisiana patient. The CDC explained that genetic testing showed changes potentially making the virus more likely to latch onto human upper respiratory tract receptors, reports .

"The changes observed were likely generated by replication of this virus in the patient with advanced disease rather than primarily transmitted at the time of infection," the CDC reported, according to Express US.

The department has issued a statement expressing its deepest sympathies to the family and friends of the deceased, confirming that no further updates will be given due to patient confidentiality. The virus has been causing sporadic, mostly mild illnesses across the US, with the majority of infections occurring among individuals working on dairy or poultry farms.

This year, there have been 65 human cases of , with 39 linked to dairy herds and 23 associated with poultry farms and culling operations. In two cases - one adult in Missouri and a child in California - health officials are still trying to identify the source of infection.

The case in Louisiana comes weeks after Canadian officials reported a teenager in British Columbia being hospitalised with a severe case of bird flu. In both instances, the illnesses were caused by a strain of the virus found in wild birds, not cattle, according to officials.