China Bird Flu Outbreak Tied to Viruses That May Hit Humans Hard
By Michelle Fay Cortez and Andrea Gerlin on April 09, 201
China’s deadly avian flu outbreak is being driven by at least two closely-related viruses, a situation that may make it more difficult to contain in humans and birds, researchers said.
The H7N9 flu has shown signs of genetic diversity since the first three patients were diagnosed, said Richard Webby, director of a World Health Organization collaborating center for the virus at St. Jude Children’s Research Hospital in Memphis. It already appears more infectious than the H5N1 strain of bird flu that has been circulating since 2003, infecting 600 people and killing 60 percent of them, he said.
Scientists from around the world are working together to understand the virus because of the potential devastation caused by novel infections. The pandemics of the past century include the 1918 Spanish flu that killed as many as 50 million people and the 2003 SARS outbreak that killed 774.
“This virus might be getting more infectious to humans,” Webby said in a telephone interview. “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 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.
“The distribution of the cases, which is over several hundred kilometers, without obvious epidemiological links, suggests that there are diverse sources,” she said in a telephone interview.
Tissue Samples
Local governments must collect tissue samples from birds at poultry markets nationwide in the hunt for the cause of the outbreak that’s killed nine people, 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.
While the number of cases has risen to 28, there is no evidence yet that the virus is spreading from human to human, World Health Organization officials said. Zambon joined other flu scientists calling for evaluation of those with human exposure to H7N9 by analyzing their blood samples for evidence of antibodies produced in response to the virus.
China Response
China has increased its capacity to respond to emerging infectious pathogens since the severe acute respiratory syndrome outbreak that caused almost $40 billion in economic losses a decade ago. SARS was easily transmitted by droplets produced when an infected person coughed or sneezed.
Chinese officials are looking at two families to see if human-to-human transmission of the H7N9 avian flu occurred, a spokesman for the World Health Organization said on Tuesday.
There’s no confirmation yet that the virus is spreading between humans, the spokesman, Gregory Hartl, said at a news conference in Geneva. Members of the same family who have the flu may have caught it from the same environmental source, he said.
Proving that may not be possible immediately if an infected family member has recovered and lacks isolates of the virus in his or her blood, said John McCauley, director of the WHO Influenza Centre at the National Institute for Medical Research in London. Evidence of past infection may not be apparent until antibodies appear in the blood, which take a few weeks.
“In one of the early cases there was the possibility of a family cluster but it was not confirmed,” McCauley said in a telephone interview. “I suspect that the clustering that is going on, whether or not it is the same zoonotic source, would be difficult to prove.”
H7N9 Samples
The H7N9 virus isolated in samples from people in China may also be potentially atypical because different samples may have different lineages, or clades, said McCauley, who has also looked at its genetic profile, which has been published on www.gisaid.org.
“One of the early viruses had a genetically distinguishable nucleoprotein gene, so that was an unusual virus,” McCauley said. “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.”
