A striking feature of the novel virus is that its H protein is structurally similar to that of viruses that don’t cause severe sickness in birds, and different from those that do, such as the H5N1 virus that has been ravaging poultry flocks in Asia since late 2002. Flu viruses that don’t sicken birds can, however, cause severe disease in humans simply because we lack any immunity to them. They also may be more lethal in people depending on how they bind to receptors in the human airways.
"If this is let spread from where it is now, it will evolve further. That's what viruses do. If it isn't contained now, that will almost certainly happen."
Scientists tracking the H7N9 virus need more information about the ecosystems of birds in China, including those in live markets, feeder farms and wild populations, to better understand and tackle the virus, said Maria Zambon, director of the U.K.'s national influenza center. That will provide a clearer view of how easily H7N9 spreads and how best to control it...
Local governments must collect tissue samples from birds at poultry markets nationwide in the hunt for the cause of the outbreak, Chinese officials said yesterday. The process is more complicated because the virus doesn't seem to harm the birds, eliminating the ability to track it by following a path of dead fowl, Webby said.
There is no evidence yet that the virus is spreading from human to human... "It's got the sort of characteristics that are somewhat unusual for a poultry virus. But the background knowledge on this is pretty sparse. It's early days still."
Further investigations are still under way to figure out whether the family cluster involved human-to-human transmission," Feng Zijian, of the Chinese Center for Disease Control and Prevention, told the newspaper.
There's no evidence yet of sustained human-to-human transmission, but the team will be looking into this," he says.
Even if the disease can be spread between humans, a pandemic is not a certainty, experts say. In order to spread quickly, the virus would need to mutate to a form that is spread through incidental or casual contact. Transmission between family members is often a first step, because they generally have prolonged contact over the course of several days.
"The Spanish flu which killed millions only had a couple percent mortality rate," he says. "If this virus mutates to be transmissible from human-to-human it will be a major issue. You have the perfect storm of pandemic flu virus in that it's highly pathogenic and could potentially be spread easily."
The genetic distance between samples collected in China suggest that this virus may have been circulating for months before it was finally detected, but in what host remains a subject of debate.
Also of concern to these researchers was the finding of the PB2 E627K mutation in the human isolates, but not in those collected from birds.
This substitution - the swapping out of the amino acid Glutamic acid (E) at position 627 for Lysine (K) – has been linked to increased influenza virulence in the past.
Remarkably, the PB2 segments of the four available human virus genome sequences from China all carry this E627K substitution, which is absent in the virus isolates obtained from birds and the environment . In addition, three of the four infections with the virus with PB2 E627K were fatal. There are two plausible explanations for this observation:
the mammalian adaptation markers are selected during replication in humans following exposure to viruses that do not have this mutation, which are circulating in animals;
the mammalian adaptation markers result from virus replication in animals from which humans become infected.
The relatively protracted disease course in the current outbreak of A(H7N9) virus infection, with relatively mild symptoms at first, followed by exacerbation in the course of a week or longer, is suggestive of the first hypothesis, similar to the outbreak in the Netherlands. (H7N7 in 2003)
Therefore, an outstanding question is whether the A(H7N9) viruses are more readily mutating in humans or milder cases are being missed.
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