>>>HONG KONG - H7N9, the latest variant of the avian flu virus, has spread 700 kilometers across three Chinese provinces since it was identified last month.  With researchers struggling to identify how the disease is transmitted, concern is mounting about its danger to humans.

Authorities culled poultry in Shanghai markets after detecting H7N9 in local pigeons. Taiwan will make anti-viral drugs available for public purchase, at a subsidized price, through April.  

While China reported that a four-year-old boy made a full recovery from H7N9 flu, of 24 known cases, seven people have died.

Professor Malik Peiris is director of the Pasteur Research Centre at Hong Kong University.

“You have to be cautious about interpreting mortality rates because, usually, only the most severe cases are investigated," said Peiris. "There could be milder cases that go unrecognized. So on the one hand this would make the mortality and the severity less. But on the other, it would mean there is more transmission occurring in humans too.”

Beginning April 11, imported live poultry will only be sold in Hong Kong after a 3-percent sample is tested for H7N9.  To develop vaccines and break the infection cycle, Peris says, the source of the outbreak must be identified.

“It is an unpredictable virus," he said. "There are hundreds of people working closely with poultry who do not seem to get infected. But there is the one person who may have quite a tenuous contact who [does]. "What is crucial is to go upstream, along the poultry marketing chain, ideally to the farms, and identify which species is the main source.”

Thomas Abraham, who wrote a book about the 2003  SARS epidemic, says the Chinese government cover-up which contributed to the spread of SARS, is unlikely to be repeated with H7N9.

“One of the early [H7N9] cases in Shanghai, even though the hospital said nothing, the patient’s admission slip was photographed and put on [the Chinese website] Weibo. This kind of information flow is a dam that is unstoppable," said Abraham.

While World Health Organization officials say there is no need for panic, Laurie Garrett, an expert at the Council on Foreign Relations, is concerned that the H7N9 death toll will rise.

“What 2009 taught us with swine flu is that global solidarity can break down very fast," said Garrett. "Countries start closing airports and quarantining travelers. They start hoarding drugs and vaccines. It is not a pretty picture.”

With public fear an issue, researchers in Hong Kong have announced they will revisit a 2009 study to confirm that surgical masks - widely worn during flu season - are indeed 70 percent effective in preventing the spread of flu viruses.