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綜合
１．從來未在H7N9在人類中出現
２．H7N9變種至可轉移至哺乳動物
３．發生了的個案互相沒有關聯
４．H7N9未令雀鳥及豬出現病徵
５．中國官員的公信力
There are reasons to be concerned about H7N9, the new strain of bird flu discovered last month in China, but there are also reasons to be reassured.
The good news is that, the new strain doesn’t appear to be highly virulent in humans, at least so far.
Fewer than a dozen cases have been documented and all have been confined to China. And while five people are reported dead -- a relatively high proportion of deaths compared to the number of infections – that’s a small number in a country of 1 billion people.
Infectious diseases expert Dr. Neil Rau says if this new virus was as easily transmissible as the H1N1 outbreak of 2009 for example, the number of infected people would be “galloping,” with new cases popping up all over the regions.
“The fact that this has been going on for at least a few months with only this amount of cases, to me, is reassuring. If this were a really serious problem, this strain, we would have many more cases by now,” he told CTV News Channel this week.
Nevertheless, the World Health Organization says there is reason to be vigilant about this new strain. Here are five reasons why:
1. It’s never been seen in humans before
Flu experts have long warned that the next flu pandemic would likely come from a new strain to which most humans would have little or no immunity.
Even the last flu pandemic, the H1N1 outbreak, turned out to be somewhat similar to other swine flus seen in humans decades ago. That’s why it’s theorized that the strain killed a relatively low proportion of seniors during the 2009 outbreak.
The World Health Organization says the new human cases of H7N9 are "of concern" because they are completely new. There have been other H7 viruses that have infected people, but never an H7 and an N9, which are the names given to the proteins of the virus' surface.
"That makes it a unique event, which the World Health Organization is taking seriously," the health agency said this week.
2. Virus has learned to adapt to mammals
The Chinese Centre for Disease Control and Prevention has sequenced the genes of H7N9 and its experts say it’s clear the strain began in birds. But the virus also showed several genetic changes that suggest it is “learning” how to attach to the airways of mammals and humans, which would allow it to spread easily.
That has the World Health Organization worried.
"The tentative assessment of this virus is that it may cause human infection or epidemic," said one of the specialists who studied the virus’ genes, director of the WHO's influenza research centre in Tokyo Dr. Masato Tashiro.
"It is still not yet adapted to humans completely, but important factors have already changed."
Flu viruses are constantly mutating and swapping genes. So far, this strain doesn’t seem to have “figured out” how to infect humans easily and allow person-to-person spread. But that remains a real possibility.
3. The cases do not appear linked
In a way, the fact that the cases have been spread out across the country is a good sign: It means the virus hasn’t developed the ability to spread easily from person to person and create “clusters” of disease. But it could also mean that humans are catching the virus from infected birds or animals.
And yet, as far as been reported, there’s been no outbreak of flu in Chinese wild birds, poultry or pigs, which are the species that most often allow animal flus to jump to humans. So experts remain baffled about how humans are becoming infected.
4. The virus appears to cause no symptoms in birds and possibly pigs
The scientists who inspected the genes of the virus samples sent to Chinese labs say H7N9 appears capable of infecting some birds without causing any symptoms. That means it could be a "silent spreader" that’s moving among birds or pigs undetected
Without obvious outbreaks of flu in chickens, wild birds or pigs, that could make it difficult to pinpoint the original infection source, as well as track its spread. That wasn’t the case with H5N1 bird flu, which caused obvious signs of illness during outbreaks, allowing farmers to perform mass culls to stop the virus’ spread.
It also makes it harder to narrow down the species that’s fuelling the virus’ spread.
"At the moment, we can't see where this virus is coming from. We don't know yet what animal source is feeding this." Wendy Barclay, a flu virology expert at Britain's Imperial College London recently told Reuters.
And, if there were no obvious symptoms in birds or pigs "nobody recognizes the infection in animals around them. Then the transmission from animal to human may occur," Tashiro told Reuters.
"In terms of this phenomenon, it's more problematic."
5. Credibility of Chinese officials
Finally, there are concerns that flu experts may not be getting the complete picture about this new virus.
In 2003, Chinese authorities initially tried to cover up the emergence of a baffling condition that became known as SARS. Chinese officials later had to apologize for their slow response and promised to be more forthright during future pandemics.
China’s Health Ministry says the government is committed to communicate details of the new strain to the outside world and its own people. The Chinese Centre for Disease Control and Prevention has already shared the genetic sequence of H7N9 with other scientists around the world.
But because two of the victims fell ill in February, some are questioning why it took so long for the government to announce the new cases.
The WHO so far has praised the Chinese government, saying it’s responding well, offering detailed case management and tracing contacts of all those known to have been infected so far.
Nevertheless, it’s likely that worries will continue that given China’s track record, authorities there may not be passing on all that they know.
With files from The Canadian Press and the Associated Press
http://www.ctvnews.ca/health/h7n9-five-reasons-the-new-bird-flu-is-cause-for-concern-1.1224231#ixzz2PbtY9ecU |
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發表於 2013-4-5 09:20
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