Human infections with influenza-A H7 viruses, a virus group that normally circulates among birds, have been rare until now, according to a researcher at Harbin Veterinary Research Institute under the Chinese Academy of Agricultural Sciences.

Tian Guobin said that in addition to human infections with H7N9 - one subgroup among the larger group of H7 viruses recently reported from China - some H7 strains, such as H7N7, H7N3 and H7N2, have in the past infected humans in other countries, including the UK, the US, the Netherlands and Canada.

The H7N9 virus was first isolated in turkeys in the US state of Minnesota in 1988, he said.