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H7N9 bird flu: what we know and don't know

The story broke in China on April 1st: a new bird flu strain, called H7N9, had emerged to infect people for the first time.

At the time, there were three known patients, two of whom were already dead. Two weeks later, the case tally continues to grow at a clipped and steady pace. The latest count, from the World Health Organization: 82 cases, 17 deaths.

H7N9 has now spread to six different provinces -- most cases are in the Shanghai area, but cases have also been confirmed in Beijing and Henan.

Source: European Centre for Disease Control and Prevention (updated as of April 15)

It can be difficult knowing how much to worry when something like this unfolds. But for now, this tweet from WHO spokesperson Gregory Hartl -- who has been actively answering H7N9 questions on Twitter -- seems to best summarize the current situation:

Not exactly reassuring -- but honest. Anything's still possible.

Given the information available so far, there is both reason to worry and reason for optimism. Here's a round-up of what we know:

The good news

*The single most reassuring piece of information right now is that there is still no evidence of sustained human-to-human transmission, which would certainly propel us into pandemic territory. There are, however, suspected cases of limited human-to-human spread that investigators are looking into -- but as the U.S. Centers for Disease Control and Prevention explains, this is not wholly unexpected and limited human-to-human transmission does not automatically mean a pandemic is nigh.

*H7N9 has not yet been found in pigs -- considered ideal "mixing bowls" for pandemic-prone viruses -- and health officials insist the dead pigs floating along the Huangpu river did not die by H7N9's hand. That being said, only 30-some pigs were ultimately tested out of more than 16,000 carcasses and the cause of these pig deaths remains a mystery. To date, the virus appears to be confined to poultry markets and has turned up in "environmental samples" as well as chickens, ducks and one wild pigeon.

*Some patients are improving or have even fully recovered, including Beijing's first case, a seven-year-old girl.

*China has invited the WHO and international experts to help with the outbreak response, including some top names in the infectious disease world. Labs around the world have also now received the virus and are busy studying its properties.

The bad news

*The world is in completely "new territory" with this new virus, according to this Canadian Press interview with WHO's senior flu expert. And there are troubling signs the virus is already well-adapted to infecting humans.

*We still have no idea what the source of the virus is despite the 48,000+ samples that have been taken from markets, farms and slaughterhouses. Are people being infected by chickens? Ducks? Pigeons? Some other bird? A still-unidentified mammal? Dust in the air? Other people? All of the above? China's Centre for Disease Control has also stated that 40 per cent of the known cases have had no contact with poultry, thus deepening the mystery of how people are getting sick.

*Unlike other avian flu strains that have caused human infections, H7N9 doesn't seem to make birds sick. This means the virus can spread silently among birds and will be difficult to stamp out through culling -- and if the virus is getting picked up by wild birds, there's no telling how far H7N9 can travel. As Nature reports, H7N9 is "poised to spread."

*The virus has now been found in a four-year-old Beijing boy who has no symptoms, making him H7N9's first known asymptomatic case. The excellent Avian Flu Diary blog has a good explainer for why this is not necessarily good news.

*Judging from a study recently published in the New England Journal of Medicine, this new bird flu strain can make people very, very sick.

*Creating a vaccine for this new flu strain will likely be very difficult.

Jennifer Yang is the Star’s global health reporter. She previously worked as a general assignment reporter and won a NNA in 2011 for her explanatory piece on the Chilean mining disaster. Follow her on Twitter: @jyangstar


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