The World Health Organization does not advise special screening for people entering Canada from China, nor does it recommend any travel restrictions, after Canadian officials confirmed a case of H7N9 bird flu, the first detected outside China.

Bernhard Schwartlander, the organization's China representative, made the remarks after a Canadian woman in her 50s was diagnosed with H7N9 bird flu after returning from a trip to China. She reported being at several places with chickens.

Canada informed the health organization about the case and urged its citizens traveling to China to avoid contact with poultry and so-called wet markets, which sell and slaughter live poultry.

"The risk of the virus spreading abroad is low, as there has been no evidence of sustained human-to-human transmission of Influenza A (H7N9)," Schwartlander said.

The WHO will continue to work closely with national authorities and technical partners in China to share information about any new cases of H7N9, he said.

The virulent bird flu virus was recognized in March 2013 in China and so far has infected about 500 people in the country, according to Hou Yunde, a virologist and academician at the Chinese Academy of Engineering.

"It has replaced H5N1 since 2013 as the dominant bird flu virus causing infections in both birds and humans here," he said.

Thirty-nine percent of the human cases have ended in death - considerably lower than the 60 percent fatality rate in humans for the H5N1 strain of the virus.

"But it's easier to infect humans with the H7N9 strain," he said.

While the virus infects both birds and humans, infected birds show no symptoms, which makes intervention and prevention of human infection more difficult, medical experts said.

Schwartlander said "the risk of virus transmission of H7N9 can be substantially reduced by applying good market practices", including the avoidance of contact with live poultry and ensuring good hygiene and regular cleaning at poultry markets. Brief closures of live markets on a regular basis for thorough cleanings, with all birds temporarily removed during the process, is encouraged, he said.

Regular sampling and testing of new batches of birds brought to a live market can help ensure earlier detection and removal of infected birds, he said.

Hou urged enhanced information exchange and cooperation between China's health and agriculture departments to curb the virus. The live poultry trade continues in many parts of the country, despite the fact that it's peak season for bird flu.

shanjuan@chinadaily.com.cn