Scientists believe that the H7N9 avian influenza virus is evolving to adapt better to human cells. A study of samples taken from recent cases of the bird flu in China shows that the virus is mutating to thrive in the cooler temperatures found in the human upper respiratory system. This suggests that the virus will be better able to infect humans.

Flu viruses carry hemagglutinin and neuraminidase activity proteins on their surfaces. Inside, they contain eight RNA segments of genetic material needed to produce new viruses. When different strains of the virus enter a host cell, the elements can recombine to create new mutant viruses.

In the case of H7N9, scientists say they have traced the virus back to three different strains of bird flu. Hemagglutinin proteins found on the virus have mutated to be more adaptable to the conditions of the human body, leading scientists to believe that it could evolve into a strain that might be transmissible between humans, and thus potentially pose the risk of a pandemic. At present, bird flu is only transmitted from bird-to-bird and bird-to-human.