Understanding the genetic make-up of currently circulating avian influenza strains may offer one of the best lines of defence against widespread human transmission, according to a recent report from the Roslin Institute.

This is according to new research that has found a key human gene responsible for blocking most avian influenza viruses from spilling over into people.

The gene, known as BTN3A3, which is commonly expressed in human airways, offers a key human defence against avian influenza.

Through a series of extensive tests, the study team was able to show that the BTN3A3 gene is vital to protecting humans against avian influenza, as most strains of the virus cannot get past its defences.

The international study into the pandemic potential of avian influenza was led by the MRC-University of Glasgow Centre for Virus Research (CVR), supported by the Roslin Institute and published in Nature.

"Identifying BTN3A3-resistant variants when they first emerge in birds might help in preventing human infections," said Ruth Maria Pinto, Roslin Institute. "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 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 were able to show that avian influenza 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, 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 spillover events in humans.

Tracking the history of influenza pandemics in humans, researchers were also able to link BTN3A3 resistance with key influenza virus types.

All human flu pandemics, including the 1918 outbreak and the swine flu pandemic of 2009, were caused by flu viruses that were resistant to BTN3A3.

As a result, this study suggests that having resistance to this gene may be a key factor in whether any flu strain has human pandemic potential.