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.