Reports of disturbing changes to the H5N1 virus circulating in Asia is causing great concern and has prompted the World Health Organization (WHO) to urge countries to prepare for a influenza pandemic.
The latest report raises concerns that changes in the molecular and disease pattern could indicate the virus is becoming more adept at infecting people. It also appears that some strains of the H5N1 virus may be developing resistance to oseltamivir, a drug wealthier nations are desperately stockpiling as fears of a pandemic rise.
Dr. Keiji Fukuda, a flu specialist from the U.S. Centers for Disease Control (CDC), who is being seconded to WHO's global influenza program, says that the report signifies the rising concern and the level of anxiety regarding the virus has risen.
The report authors do however concede that they have limited scientific evidence on which to determine whether H5N1 is becoming an even graver risk to mankind, but according to Fukuda they are concerned that that is what might be happening.
These alarming changes are being observed in the northern part of Vietnam where Fukuda was part of a recent three-person WHO mission to the country.
One leading U.S. epidemiologist, Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, says the report contains no single smoking gun to suggest H5N1 is becoming a pandemic strain, but the combined evidence paints a compelling picture that cannot be ignored, and that H5N1 is "headed in the direction that none of us would like to see it go".
The report of a case where the virus was partially resistant to oseltamivir will worry public health officials around the world.
Oseltamivir, sold as Tamiflu, is one of only two antiviral drugs known to work against H5N1 and is the first choice for pandemic planners because it is easier to use than the alternative, zanamivir.
Dr. Frederick Hayden, an antiviral expert at the University of Virginia, insisted it wasn't necessarily disturbing to find limited resistance to the drug because it has also been documented in a small percentage of infections with human flu strains.
Although the finding raises the spectre of a resistant strain of the virus becoming dominant and spreading among people, creating a situation where the world has virtually no therapeutic weapons to combat pandemic flu in the months before a vaccine could be produced.
Hayden also says that human flu strains resistant to oseltamivir are generally less fit and don't transmit as well.
But Dr. Earl Brown, an influenza virologist at the University of Ottawa, said oseltamivir is too new a drug for anyone to assume that pattern will persist across all subtypes of influenza.