Bird flu virus strain not transmissible
The latest bird flu virus that killed a 39-year-old bus driver in the southern Chinese city of Shenzhen over the weekend is not yet transmissible between humans, Chinese health authorities said. The man, who lived in Shenzhen just across the border from Hong Kong, died from multi-organ failure on Saturday, a week after being admitted to hospital with a fever brought on by the virus, state media reported.
“The virus found in the patient was 90 percent similar to H5N1 viruses previously isolated in ducks in China, which suggested that the man was very likely to have been infected through direct contact with a bird,” the Shenzhen Center for Disease Prevention and Control said in a statement. “It is still not transmissible between people,” it said, adding that the bus driver was probably infected through direct contact with birds.
Hong Kong's Centre for Health Protection said on Monday that the virus strain found in the man was very similar to that recently found in wild birds in Hong Kong. An analysis of its genes also found that the virus can be treated by amantadine, a common antiviral drug. The virus is normally found in birds but can occasionally jump to people. Researchers worry that the virus could mutate into a form that would spread easily between humans.
More than 19,000 birds at a Hong Kong market were slaughtered and imports and sales of live poultry were banned for three weeks after a chicken carcass tested positive for H5N1. Lab tests later confirmed that an Oriental magpie robin found dead on Dec. 17 was also infected.
The Guangdong health department has said 120 people who had close contact with Chen have not developed any abnormal symptoms. The World Health Organization says 336 people have died from 573 confirmed bird flu cases since 2003. Of these, 40 cases were in China, 26 of which were fatal. China's last reported human case of H5N1 was in June 2010. A pregnant 22-year-old woman from central Hubei province died after being exposed to sick and dead poultry.
Human transmission studies with bioterrorism potential withheld
Two new studies where scientists had genetically altered a deadly flu virus to make it more contagious have provoked fear, even outrage, in some quarters. Biosecurity advisers to the American government, which paid for the research, have urged that full details not be published for fear that terrorists could make use of them. The World Health Organization warned Friday that while such studies were important, they could have deadly consequences.
Some scientists suggest that such research should not even have been done, since the modified virus could slip out of a lab and set off a lethal epidemic. Others contend that such experiments are essential to learning what naturally occurring changes in flu viruses are the most dangerous. The results could help inform efforts to predict epidemics, they say, and to develop antiviral drugs and vaccines.
The important property that makes these man-made or natural viruses important is their ability to be transmitted from human to human determining whether it can cause a pandemic. Contagion depends on a complex interplay between a virus and its victim, including where it enters the body, the types of cells in which it can reproduce and whether it can then escape to reach another human.
The virus that scientists made more contagious was the A (H5N1) avian flu. In its natural form, it is known to have infected only about 600 people since its discovery in 1997, but it killed more than half of them. Humans almost never transmit it to one another. But if that ever were to change, bird flu could become one of history’s worst pandemics.
The work to make the virus more transmissible was done by two separate groups, one at Erasmus Medical Center in Rotterdam, in the Netherlands, and the other at the University of Wisconsin. The experiments were performed on ferrets, because flu behaves in them almost exactly as it does in humans.
In Rotterdam, a team led by Dr. Ron Fouchier made a strain of bird flu that could drift through the air into nearby cages and infect other ferrets. Although that result has set off worldwide concern, some researchers say the modified virus might not behave the same way in people, because ferrets are not a perfect model for human transmission.
The new virus does not seem as contagious as either the 1918 Spanish flu or the 2009 swine flu, Dr. Fouchier said. To become airborne, the virus required a range of genetic modifications — “a combination of everything,” he said. He explained that in humans bird flu viruses live best in the lower lungs which makes it harder for them to escape in sneezes and coughs. If one could replicate in the upper airways, it would be more likely to be released as an aerosol and might be more transmissible. If the virus were shed, or expelled, as individual particles instead of in clumps, said Dr. Fouchier, it would be more easily spewed out in the tiny droplets of a cough. “It also may help if the virus induces coughing or sneezing,” Dr. Fouchier added.
Modifications to any of these viral traits may help make the bird flu virus more contagious. And in fact, it took only a few mutations to make the new virus, he said. Dr. Fouchier declined to describe them in detail. But other scientists said increased transmissibility usually depends on changes in at least two of eight genes: one that helps the virus invade cells, and one that helps it copy itself. In birds, flu is primarily a gut disease, shed in feces, whereas in people it is primarily a nose, throat and lung disease, shed in saliva and mucus.
Researchers have found that a small change in a gene called PB2 helps make a type of bird flu contagious in ferrets by enabling the virus to copy itself at the temperatures found in a mammal’s nose, which is 4 degrees Celsius cooler than a bird’s intestines.
Ram Sasisekharan, a Massachusetts Institute of Technology researcher on a team that did a 2009 study that made a bird flu more transmissible in ferrets, said another crucial mutation was in the HA gene, which codes for the hemagglutinin spike that attaches the virus to cells. The mutation slightly changed the shape of the spike, making the virus more transmissible. Dr. Sasisekharan’s study did not involve A (H5N1) bird flu. Instead, the researchers started with a type of duck flu and spliced in genes from the highly contagious 1918 Spanish flu.
There is one reassuring note in the unsettling findings from Rotterdam and Wisconsin. Fearsome though it may be, the new virus appears to be vulnerable to existing vaccines and flu drugs.
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