When I began blogging regularly on the H5N1 pandemic threat last January, the bird flu virus had just swept out of its Asian stronghold and had appeared in places like Iran and Turkey for the first time. The geographic spread of the virus progressed from roughly 15 countries in late 2005 to nearly 50 countries by the end of 2006. Suddenly, bird flu wasn’t just a problem for S.E. Asia anymore; it was a problem for the world.
Since its discovery in 1996, the virus has mutated into several distinct strains, with the new fujian-like strain reportedly spreading across China. Along the way, the virus appears to have picked up the ability to survive at higher temperatures and in some instances, appears to have a greater affinity for the receptor cells found in the upper airway passages.
The Case Fatality Ratio (CFR) of the virus has also increased this year, going up from roughly 50% last year, to in some areas, nearly 75%. This is an ominous trend, and goes against the conventional wisdom that states that a virus must lose lethality as it gains transmissibility. Late in 2006, the WHO (World Health Organization) finally admitted the possibility that the virus’s mortality rate might not drop, even in a pandemic.
We also had confirmation of the first suspected H2H (Human-to-Human) transmission of the virus, in the Karo Cluster in Indonesia last May. Other H2H transmission is suspected, but it is very difficult to prove.
2006 also brought with it news that hosts other than birds, and the occasional human, were being infected. We’d known about tigers in 2004 that had been fed infected bird carcasses coming down with the virus, but it wasn’t until 2006 that we had confirmation of dogs, cats, pigs, and martens (a weasel-like mammal) contracting the disease.
Additionally, we learned late in the year that infected birds were shedding the virus, not just in their droppings, but through their respiratory tracts, which is unusual for an avian flu virus. We also recently learned that previously unsuspected bird species, such as pigeons and sparrows, could be major vectors of the virus.
At the risk of anthropromorphizing the virus (they really hate that!), the H5N1 pathogen has obviously been learning new tricks.
Whether any of these changes mean we are closer to a pandemic is impossible to tell. An influenza virus is either a pandemic strain, capable or sustained H2H (Human-to-Human) transmission or its not. So far, the H5N1 virus hasn’t made that leap.
What we do know is the virus is not static; it changes as it infects new hosts, and while most of these changes are evolutionary dead ends, some of them appear to make the virus more a competent pathogen.
There are some scientists who believe that since the virus hasn’t made the jump to a pandemic strain yet, it is unlikely to. Other scientists, watching the changes over the past decade, see a real potential in this virus, and believe it is a contender for the next pandemic.
Only time will tell.
While there are many ominous signs, there are no clear signals, no absolute indicators. This is a threat that will remain with us for years to come, spreading throughout the world on the wings of migratory birds, hidden in mammalian hosts as yet unidentified, and always changing, always mutating.
Today, the virus is more widespread than it was a year ago. It is also more diverse, having developed more mutations, and strains. It is evolving.
While the endgame of this evolutionary experiment is uncertain, the smart money says we dare not take our eyes off of this threat. We may, or may not see a pandemic in 2007.
But one thing is almost certain.
The H5N1 virus will likely learn some new tricks in the coming year. And they will be interesting to watch.