Researchers from the Universite Libre de Bruxelles (ULB), the International Livestock Research Institute (ILRI), Oxford University, and the Chinese Center of Disease Control and Prevention analyzed new data showing the distribution and density of live poultry markets in China and of poultry production overall in the country.
They found that the emergence and spread of the disease up until now is mainly linked to areas that have a high concentration of markets catering to a consumer preference for live birds and does not appear related to China's growing number of intensive commercial poultry operations.
They have pinpointed areas elsewhere in Asia with similar conditions (places with a high density of live bird markets) that could allow H7N9-which has infected 429 people thus far and killed at least 100-to significantly expand its range.
Places at risk include urban areas in China where the disease has not yet occurred, along with large swaths of the Bengal regions of Bangladesh and India, the Mekong and Red River deltas in Vietnam, and isolated parts of Indonesia and the Philippines.
"We're not saying these are areas where we expect to see infections emerge, but the concentration of bird markets makes them very suitable for infection should the virus be introduced there, and that knowledge could help guide efforts to limit transmission," Marius Gilbert, an expert in the epidemiology of livestock diseases at ULB and the paper's lead author said.
Gilbert and his colleges developed a "risk map" for H7N9 in part to help anticipate where human infections-so far caused mainly by contact with birds and not through "human to human" transmission-might occur next.
Unlike H5N1, the other virulent form of avian influenza to emerge in recent years, H7N9 produces little signs of illness in birds, which means it could move stealthily into poultry populations long before people get sick.
The study is published in the journal Nature Communications.