August 1, 2006
Researchers at the Centers for Disease Control and Prevention (CDC) have used a newly developed research method to investigate the ability of a lab-engineered combination of the bird flu virus and a more common human virus to spread in lab animals.
The H5N1 virus does not yet have the ability to spread efficiently from one human to another, which has so far prevented the virus from causing a pandemic.
In a series of experiments, published in the July 31 issue of the journal Proceedings of the National Academy of Sciences, genes from a human H3N2 flu virus were added to genes from an H5N1 bird flu virus to create new hybrid viruses.
The new viruses were tested in ferrets because their susceptibility to flu viruses is similar to that of humans. The animals were then placed in close proximity, to see if infected ferrets passed the new virus to uninfected animals and whether they transmitted it more easily than the original H5N1 virus.
In this test, human H3N2 viruses transmitted efficiently between the ferrets, but avian H5N1 viruses did not. When the hybrid viruses were tested it was found that these viruses also did not pass easily between ferrets.
"This important science has established a new research method to help us learn more -- in advance -- about the genetic changes that enable new influenza viruses to spread efficiently and in a continuous manner among people," said CDC Director Dr. Julie Gerberding.
"H5N1 viruses continue to spread among birds worldwide and their genetic properties are constantly changing. There is an urgent need to better understand how these viruses could acquire the ability to spread efficiently between people. This research increases our knowledge, and may enable us to more quickly identify H5N1 viruses and other influenza viruses that have the potential to cause a pandemic," she added.
Most influenza experts believe another pandemic will occur, but it is impossible to predict which strain will emerge as the next pandemic strain, when it will occur or how severe it will be. As of late July, H5N1 had caused more than 230 cases of disease in humans worldwide and is widespread in bird populations in Asia, Africa and Europe.
However, the virus has only rarely passed between humans and does not currently transmit easily from human to human. H5N1 avian viruses have not been found in the United States in either birds or humans.
