(Nature) An engineered influenza virus based on a haemagglutinin protein from H5N1 avian influenza, with just four mutations, can be transmitted between ferrets, emphasizing the potential for a human pandemic to emerge from birds.
Influenza pandemics in humans arise from animal influenza viruses, yet the molecular changes required for an animal virus to be transmitted efficiently between humans are poorly understood. Highly pathogenic H5N1 avian flu viruses have circulated in poultry for more than 16 years, only rarely resulting in human infections. But when people do catch H5N1 bird flu, their disease is of unusual severity, raising concerns that a human H5N1 pandemic might have a catastrophic impact on public health. However, an H5N1 virus that can be efficiently transmitted from human to human has not yet emerged, leading some researchers to question whether these viruses are inherently incapable of acquiring this capacity. On page 420 of this issue, Imai et al.1 demonstrate that H5N1 viruses do have the potential to cause a human pandemic. The authors identify mutations in the avian virus that permit viral transmission between ferrets by means of respiratory droplets — the best available model for influenza transmission in humans.