Aug 1 2006
A team of scientists at the U.S. Centers for Disease Control and Prevention (CDC) have developed a new research method that may help identify the types of genetic changes that would be necessary for the avian influenza virus (H5N1) to be more easily transmitted among people.
At present bird flu fortunately does not appear to have an efficient and sustained human-to-human transmission property that is needed to cause a pandemic; but viruses can evolve into epidemic and pandemic forms by mixing their genetic material with other viruses.
The scientists used the new process to find out how a lab-engineered combination of the avian influenza virus and a more common human virus would spread in laboratory animals.
They wanted to understand the genetic changes that are needed for an H5N1 virus to acquire the genetic changes needed to cause a pandemic.
CDC scientists designed and tested a research method that involved three elements: ferrets; a caging system that enabled researchers to put healthy and infected animals in close proximity; and reverse genetics, a tool for combining the genes from human and avian influenza viruses.
The team mixed genes from a human H3N2 influenza virus to genes from an H5N1 avian influenza virus in order to create new hybrid viruses.
Infected ferrets were either placed in the same cage with uninfected ferrets to test transmissibility by close contact or in adjacent cages with perforated walls to test spread of the virus by respiratory droplets.
Dr. Jackie Katz one of the lead researchers at the CDC's Influenza Branch says the work was carried out in high-security labs to eliminate any risk to the public.
The human H3N2 viruses transmitted efficiently between the ferrets, but avian H5N1 viruses did not and when the hybrid viruses were tested it was found that these viruses also did not pass easily between ferrets.
Julie Gerberding CDC Director says the findings are a concern because the data does not mean that H5N1 cannot convert to be transmitted from person to person, but rather suggests that it is a complex process.
According to Gerberding there are more than 50 possible combinations of the viruses, and Katz and her team could have created a dangerous strain of flu.
The H5N1 virus remains essentially a disease of birds which is quite difficult for humans to contract and usually entails contact with sick or infected birds.
The virus has spread across much of the world and has killed 134 people out of 232 known to be infected and is widespread in bird populations in Asia, Africa and Europe.
H5N1 avian viruses have not been found in the United States in either birds or humans.
Most influenza experts believe another pandemic will occur, but say it is impossible to predict which strain will emerge, when it will occur or how severe it will be.
The few human transmissions have been between blood-related close family members living together in confined spaces.
The researchers noticed that the ferrets sneezed when they were infected with a normal H3N2 virus, but not when they were infected with the genetically engineered strain and say this suggests the ability of the virus to make its victims sneeze and cough is key to transmitting it.
Dr. Katz says there is much still to be learned and as influenza viruses are constantly changing vigilance is vital in the continuation of the research to understand the possible virus combinations or emerging changes in the H5N1 viruses that would increase the risk of a pandemic strain emerging.
The research is published in the Proceedings of the National Academy of Sciences.
Pandemic linked to 16% rise in babies born with heart defects