NEW research has found a key human gene responsible for blocking most avian flu viruses from spilling over into people. 

An international study led by scientists at the MRC-University of Glasgow Centre for Virus Research (CVR) identified the human gene BTN3A3, commonly expressed in airways.

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Through a series of tests, researchers showed that most strains of the virus could not get past the gene’s defences.

Since 2022, there has been a rise in bird flu cases worldwide in both domestic and wild birds. 

While the disease mainly affects birds, it has been known to spill over into other species, including, in rare cases, humans. 

Spill over

For example, the 1918 Spanish flu virus, which caused more than 25 million deaths worldwide, is believed to have originated from an avian strain.

However, experts agree there are still several gaps in knowledge that make it challenging to predict which variant of avian influenza virus might spill over into the human population and when.

The team behind this study compared the behaviour of hundreds of genes by human cells during viral infection with either human seasonal viruses or avian flu viruses. 

The study showed that the BTN3A3 gene could block the replication of avian flu in human cells. 

Seasonal flu

In contrast, the seasonal human flu viruses, which infect the human population regularly, are resistant to BTN3A3 meaning they cannot successfully block them.

The team also looked at avian flu viruses that occasionally do infect humans, for example, H7N9, which since 2013 has infected more than 1,500 individuals with a 40% case fatality rate. 

Researchers showed that avian flu viruses like H7N9 have a genetic mutation that allows them to ‘escape’ the blocking effects of the BTN3A3 gene.

Finally, when studying the evolution of avian flu strains, the scientists were also able to show that there had been an increase in the number of BTN3A3-resistant strains circulating in poultry around the same time as spill-over events in humans.

Rute Maria Pinto, the first author of this study, said: “Identifying BTN3A3-resistant variants when they first emerge in birds might help prevent human infections. 

“Control measures against emerging avian flu viruses can be tailored specifically against those that are BTN3A3-resistant, in addition to other genetic traits known to be important for zoonotic transmission.”

The study, ‘BTN3A3 evasion promotes the zoonotic potential of influenza A viruses’ was published in the journal Nature.