Since the announcement of a government financed study to determine how the H5N1 virus spreads was announced last week, there has been a great deal of controversy about the release of the data. 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.
Scientists do not know everything about what makes a virus transmissible — and much they must learn before they are able to prevent another flu pandemic. Contagion (communication of disease from one person to another by close contact not the movie) 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 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. To become airborne, the virus required a range of genetic modifications. Dr. Fouchier noted that the most successful virus would be one that:
- Lives in the upper airways (versus the lower lungs as H5N1 does now) to ease release as an aerosol.
- Shed, or expelled, as individual particles instead of in clumps, where it would be more easily spewed out in the tiny droplets of a cough.
- Induces coughing or sneezing.
To increase 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.
Excerpts of the studies are being released today for those who are dying to know more…