Advisors of biosecurity to the US Government, which paid for the research, asked that details not be published for fear that terrorists could make use of them.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 believe that research should not even have been made, since the modified virus could drag a laboratory and triggered a deadly epidemic. Others argue that such experiences are essential to learn what natural changes in the influenza viruses are more dangerous. The results could help inform efforts to predict epidemics, they say and develop vaccines and antiviral drugs.
It is a point on which the factions agree: the ability of a virus to spread easily from one person to another is the key to determine whether it can cause a pandemic. There is much scientific do not know what makes a transmissible virus - and that they must learn to prevent an another influenza pandemic. Contagion depends on a complex interaction between a virus and the victim, including when it enters the body, the types of cells in which it can reproduce, and it may then escape to another human being.
Made more contagious than scientific virus was influenza avian influenza. In its natural form, it is known to have infected only about 600 people since its discovery in 1997, but it has killed more than half of them. Human it almost never transmit to each other. But if it ever change, avian influenza could become one of the worst pandemics in history.
Work to make more transmissible virus was made by two separate groups, one at the Erasmus Medical Center in Rotterdam, in the Netherlands and the other at the University of Wisconsin. The experiments were conducted on ferrets, because flu behaves in their almost exactly as it does in humans.
Rotterdam, a team led by Dr. Ron Fouchier in a strain of avian influenza which could derive in the air in cages nearby and infect other ferrets. Although this result has raised concern in the world, some researchers say the modified virus could not behave in the same way in people, because the ferrets are not a model for human transmission.
The new virus appears not as contagious as the 1918 Spanish flu or influenza swine 2009, said Dr. Fouchier. To become airborne, the virus required a range of genetic modifications - "a combination of everything", he said.
In humans, avian flu, virus live better in the lower lungs, he said, which makes it more difficult for them to escape in the sneezing and coughing. If could replicate in upper airway, it would be more likely to be released as an aerosol and perhaps more transmissible.
If the virus have been delivered or expelled, as individual particles instead of in clumps, said Dr. Fouchier, it might be more easily vomie in tiny droplets of a cough.
"It also can help if the virus causes coughing or sneezing," added Dr. Fouchier.
Viral changes to one of these traits may help make the most contagious bird flu. And in fact, it took only a few changes to make the new virus, he said.
Dr. Fouchier refused in detail. But other scientists said increased transmissibility usually depends on changes in at least two of the eight genes: one which helps the virus invade cells, and which helps to copy itself.
In birds, influenza is primarily a bowel disease, shed in feces, while among people, it is mainly a nose, throat and lung disease, shed in the saliva and mucus.
Researchers have found that a small change in a gene called PB2 helps make a type of ferrets contagious avian influenza by enabling virus copy itself to the temperatures found in the nose of a mammal, which is 4 degrees Celsius colder than the intestines of a bird.
RAM Sasisekharan, a researcher at the Massachusetts Institute of Technology on a team that did a study of 2009 that an avian flu more transmissible ferret, said an another mutation crucial gene HA, which codes for the Spike hemagglutinin attaches the virus to the cell. The mutation has slightly changed the shape of the spur, making more transmissible. Dr. Sasisekharan study did not influenza avian influenza. Instead, researchers have begun with a type of duck influenza and spliced in the genes of the Spanish flu of 1918 highly contagious.
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