An Explanation of How Avian Flu Spreads
Recent reports that two teams of scientists had genetically altered a deadly flu virus to make it more contagious have provoked fear, even outrage, in some quarters.
CULLING Health workers in Hong Kong killed about 17,000 chickens at a wholesale poultry market after a case of avian flu was discovered in a bird there last month.
Biosecurity advisers to the American government, which paid for the research, have urged that full details not be published for fear that terrorists could make use of them.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 argue that the 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.
There is one point on which the factions agree: The ability of a virus to spread easily from person to person is the key to determining whether it can cause a pandemic. There is much scientists do not know about what makes a virus transmissible — and much they must learn before they are able to prevent another flu 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.