Finches, parakeets and sparrows are the ultimate source of H7N9 avian influenza, a new study concludes. More than 600 people have contracted H7N9 bird flu in China, and more than 200 have died. Most of the people probably caught it from infected chickens, but it hasn’t been clear where chickens pick up the virus.

In laboratory experiments, society finches spread H7N9 from their mouths into water when they drank, researchers report in the April Emerging Infectious Diseases.

Chickens and quail could then be infected by drinking that same water, the researchers found. The virus does not seem to spread between birds through the air. It is unclear how the H7N9 virus re-emerged and how it will develop further; potentially it may become a long-term threat to public health.

The H7N9 viruses have spread from eastern to southern China and become persistent in chickens, which has led to the establishment of multiple regionally distinct lineages with different reassortant genotypes. Repeated introductions of viruses from Zhejiang to other provinces and the presence of H7N9 viruses at live poultry markets have fuelled the recurrence of human infections.

This rapid expansion of the geographical distribution and genetic diversity of the H7N9 viruses poses a direct challenge to current disease control systems. It’s likely to suggest that H7N9 viruses have become enzootic in China and may spread beyond the region, following the pattern previously observed with H5N1 and H9N2 influenza viruses