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Another person has fallen ill with bird flu in the United States, but this time, public health officials don't know how they caught the highly pathogenic avian influenza virus (HPAIV).
Thankfully, the patient has recovered, but they are the 14th person to fall ill with bird flu in the US this year, and the first patient with "no immediate known animal exposure", according to the Centers for Disease Control and Prevention (CDC).
All previous human cases were among workers who had contracted the virus from sick animals on poultry or dairy farms. This new case is a mystery the CDC is desperately trying to solve.
On August 22, an adult patient tested positive for the avian virus at a hospital in the state of Missouri, where only poultry and wild birds have previously tested positive for the H5N1 strain of the virus.
Initially, the patient tested positive for influenza A, but they didn't match any known human subtype. Further testing revealed the patient had somehow picked up the avian influenza, which is currently spreading among wild and domesticated birds and mammals across the US, as well as Europe, South America, Africa, parts of Asia, and the Antarctic.
This person had no known contact with animals, although it is possible they were exposed to an infected animal without their knowledge.
Officials at the CDC are now sequencing the viral genome of this recent human case to better understand where the pathogen came from and how it might have adapted to infect mammals like ourselves.
The patient in Missouri has not passed the virus on to any close contacts, and without any known case of human to human transmission thus far, the CDC still lists the threat of avian flu to the public as "low".
"The risk of sustained transmission or infection among the general public remains low," confirms the Missouri Department of Health and Senior Services.
The fact that this patient ended up in hospital is a concerning sign, however; it is unknown at this point whether their severe symptoms were due to the virus itself or to underlying medical conditions.
Deputy director of the CDC, Nirav Shah, told The Guardian in an exclusive interview in July that their team is carefully watching for increasing severity of avian flu in humans, as this could indicate the virus is mutating in a way that could be dangerous to public health.
"If we were to see individuals with no connection to a farm whatsoever, or chicken exposure, developing signs and symptoms – that would be greatly concerning," Shah said at the time.
The recent case in Missouri is the first case of bird flu detected as part of the nation's flu surveillance system, under which curious forms of influenza are sent for further testing.
