It’s like buying two tickets instead of one for the national lottery, you may shorten the odds ever so slightly, but there’s still very little chance of winning. That should be your first thought on hearing that the strain of avian influenza currently making the media sweat has evolved into two distinct variants. That’s the big news emerging from the International Conference on Emerging Infectious Diseases in Atlanta this week.
Rebecca Garten of the US Centers for Disease Control and Prevention reports that she and her colleagues analysed more than 300 H5N1 samples from infected birds and people between 2003 and summer 2005, and found two distinct sub-types of the virus. The genetically distinct H5N1 strain is thought to have emerged in 2005 and infected people in Indonesia.
The concern is that the existence of this variant points to an increased risk of a human-transmissable form of avian influenza emerging at some stage. Of course, the emergence of distinct strains of a single type of flu virus is nothing remarkable. Flu viruses are notoriously quick to evolve. After all, they wouldn’t be endemic in their host populations if they weren’t, as a second wave of infection would simply be defeated by the already primed immune defences. Evolution provides each successive strain with a new set of proteins to avoid detection by the immune system. Regardless, H5N1 is still a bird virus, it only very rarely infects people. It will take more than a simple single mutation to allow it to leap from a bird host environment to humans and even then, many researchers concede that it is likely to lose virulence when it does so.