Thursday, August 25, 2005

Geographic spread of H5N1

On August 18, WHO issued a statement calling attention to what we have become accustomed to hearing from the daily bird flu news feed: H5N1 has greatly expanded its geographic range. Starting in 1996 in southern China, it moved to Hong Kong in 1997, where it infected a number of people. After a hiatus where no infections were reported, it reappeared in 2003 in Hong Kong, swept into southeast asia where it has infected over a hundred people killing half of them, become entrenched in western China and eastern Russia and Kazakhstan, been found in wild birds in Mongolia and is poised to enter Europe (if it hasn't done so already).

Despite Draconian measures which have involved killing over 100 million birds, the geographic spread of H5N1 has been inexorable and unstoppable. WHO's statement goes on to mouth their usual platitudes about how most human cases to date have involved close contact with poultry, the need for continued surveillance, etc., etc., but finishing with the real bottom line:
The expanding geographical presence of the virus is of concern as it creates further opportunities for human exposure. Each additional human case increases opportunities for the virus to improve its transmissibility, through either adaptive mutation or reassortment. The emergence of an H5N1 strain that is readily transmitted among humans would mark the start of a pandemic.
If it hasn't already started somewhere. All previous pandemics have had a subterranean prologue of smoldering human infection, below the radar screen, followed by sudden explosive spread. Given the relative inability most of the countries where the disease is now endemic in poultry to mount effective surveillance efforts, I wouldn't be too confident.