H7N9 virus can transmit via air-borne exposure among mammals

The human-isolated avian influenza A (H7N9) virus can infect ferrets, the main mammal model for research into human influenza, and transmit from ferret-to-ferret via close contact and air-borne exposure, albeit the latter less efficiently, according to a report released on Friday by Hong Kong experts.

Meanwhile the report by Hong Kong University (HKU) Li Ka Shing Faculty of Medicine said that no "direct evidence" yet confirms human-to-human transmissibility.

The research was published on the latest Science, the prestigious international scientific journal. It also finds that pigs can be infected by the H7N9 virus, leading to mild visible clinical signs and pneumonia, so the surveillance of pigs is needed to prevent the epidemic from spreading further.

To date, a total of 130 laboratory-confirmed cases of human infection with H7N9 virus have been reported on the Chinese mainland since March this year, causing 36 dead, and the case of "Family Cluster" in Shanghai and Shandong aroused concerns towards the potential risks of human-to-human transmissibility.

Guan Yi, professor of School of Public Health at HKU, said there is no "direct evidence" that has proved the virus can transmit human-to-human. "If the limited possibility of human-to- human transmissibility ranges on the scale of 1 to 10, I'd like to put it at one. It is very low."

However, the chance of H7N9 virus evolving further to form the basis of a future pandemic threat cannot be excluded, Guan said, adding public health measures should thereby be well maintained.

Since H7N9 virus has the possibility to infect mammals, such as human, pigs and ferrets, the research team suggests that for better disease control and prevention, the health authorities should also take into consideration of other poultry and pets which may have a chance to be contacted with the virus.

In addition, the infected animals do not necessarily develop fever and other related clinical signs, indicating that asymptomatic infections among human are possible.

Guan led the research team, in collaboration with the National Influenza Center, Chinese Center for Disease Control and Prevention.