After more than a decade where H5N1 pretty much dominated the avian flu scene (albeit not totally alone, with LPAI H5's, H7's & H9N2 in the mix), over the past couple of years we've watched as a small handful of new reassortant avian flu viruses have emerged in China, and have begun to spread.
First to emerge was the H7N9 virus - low path in birds, but highly pathogenic in humans - in March of 2013 in Eastern China.
Since then more than 640 H7N9 human infections have been reported. This was followed in December of 2013 with H10N8, which has infected three people, and a few months later by H5N6 which has aslo infected three people in China.
While they haven't infected humans yet, we've seen the emergence of several highly pathogenic H5 viruses (H5N8, H5N2, H5N1 N/A) all based on a Chinese H5N8 virus that took off in Korean poultry in January of 2014, and has since spread to both Europe and North America.
And although it is hardly a new player, in 2013 we saw the first human infection by H6N1 in Taiwan.
Suddenly we find ourselves with a very crowded - and still growing - avian flu field.
And it isn't as if each one of these subtypes only comes in one flavor. The H7N9 virus has, at last count (see Nature report), produced at least 48 genotypes, spread across three major clades, and it is likely that constellation of H7N9 variants continues to expand.
So when we discuss a flu virus – like H5N1, H7N9 or H5N8 – we aren’t talking about a single, monolithic threat. We are talking about an ever-expanding family of related viruses, which can vary considerably in their behavior and the threat they pose (see Differences In Virulence Between Closely Related H5N1 Strains).
All of which serves as prelude to a very nice review of the evolution and epidemiology of avian flu viruses in China, published this week in the Journal of Virology:
Novel reassortants of H7N9, H10N8, and H5N6 avian influenza viruses (AIVs) are currently circulating in China's poultry flocks, occasionally infecting humans and other mammals. Combined with the sometimes enzootic H5N1 and H9N2 strains, this cauldron of genetically diverse AIVs pose significant risks to public health. Here, we review the epidemiology, evolution and recent outbreaks of AIVs in China, discuss reasons behind the recent increase in the emergence of novel AIVs, and identify warning signs which may point to the emergence of a potentially virulent and highly transmissible AIV to humans. This review will be useful to authorities who consider options for the detection and control of AIV transmission in animals and humans, with the goal of preventing future epidemics and pandemics.
The entire paper is available as a PDF File, and is well worth reviewing.
Two areas touched on in this study are those that we've discussed often over the past few years, First is the integral role that LPAI H9N2 has played in the emergence and continual evolution of these highly pathogenic avian viruses (see cites below):
And second on how the use of poorly matched vaccines may have driven the evolution of `vaccine escape' viruses (see cites).
Unfortunately, even as the threat seems to be escalating in China from these emerging viruses, we have seen as marked decline in the quality (and timeliness) of reporting of outbreaks by Chinese health officials over the past 6 months (see China Reports 15 H7N9 Cases in May, 7 Deaths ).