China’s avian flu outbreak that has killed nine people since March 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 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.
“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.
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, WHO 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.
A four-year-old boy in Shanghai has become the first patient to recover from H7N9 bird flu, China’s official Xinhua News Agency reported today. The country recorded a further three infections, taking the case total to 31, the National Health and Family Planning Commission said on its website.
A woman in Anhui and a man in Jiangsu died yesterday, the first deaths in the two provinces. The 35-year-old woman fell ill March 15, according to the health department in Anhui province. The Jiangsu man was 83, the province’s health department reported.
Authorities have detained 11 people across China since April 7 for spreading rumors about H7N9, state-run Xinhua News Agency reported today. The cases include three men in Guizhou who will be held for five to 10 days for sending messages on their microblogs about the virus being found in a live poultry market in the southwestern province, Xinhua said on its website.
To date, cases reported by authorities have been confined to eastern China -- in Shanghai and in Anhui, Jiangsu and Zhejiang provinces.
The Shanghai Composite Index closed little changed today. The gauge ended at its lowest level this year on April 8 because of concern about the spread of the virus.
The market impact will probably remain muted “for weeks at most” even if human-to-human transmission occurs, Tracy Tian and David Cui, analysts at Bank of America Merrill Lynch, wrote in an April 9 report. Possible under-performing industries include chicken and pig farms, airlines, public transport, hotels and travel agencies, they wrote.
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 WHO said yesterday.
There’s no confirmation yet that the virus is spreading between humans, Gregory Hartl, the WHO spokesman, said at a briefing 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 would 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.”
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, 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.”