China, which is (by far) the world's largest producer of pork (see chart below), raises as many pigs as the next 10 biggest pork producing countries combined.
And while swine around the world carry and spread a variety of H1, H2, and H3 Swine Influenza Viruses (SIVs), a 2013 survey of the Epidemic Status of Swine Influenza Virus in China also documented the presence of avian H3N8, H4N8, H5N1, H6N6, and H9N2 in Chinese pigs.
Swine possess both avian-like (SAα2,3Gal) and human-like(SAα2,6Gal) receptor cells in their respiratory tract, making them susceptible to a wide variety of avian, human, and swine influenza viruses.
This allows them to act as a `mixing vessels', which can lead to the creation of new hybrid flu viruses.
As the diversity of the pool of flu viruses circulating in pigs increases, the odds of generating new biologically fit novel viruses increases. Over time, reassortants of reassorted viruses are generated, and we end up with viruses with multiple parental contributions.
Over the past several years we've seen both swine variant viruses (like H1N1v, H1N2v, & H3N2v) and novel swine/human flu variants emerge around the world.
A few recent blogs include:
Since the influenza subtypes that commonly circulate in swine (H1, H2 & H3) are also the same that have caused all of the human pandemics going back 130 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), they are generally regarded as having less far to `jump’ to humans than many avian viruses.
Which is precisely how the H1N1 pandemic virus emerged in 2009, after kicking around (and reassorting in) swine herds for a decade or longer.
So we watch with interest reports - like the one below - of novel swine flu viruses emerging anywhere in the world.
A Novel H1N2 Influenza Virus Related to the Classical and Human Influenza Viruses from Pigs in Southern China
Yafen Song1, Xiaowei Wu1, Nianchen Wang1, Guowen Ouyang1, Nannan Qu1, Jin Cui1, Yan Qi2, Ming Liao1* and Peirong Jiao1*
- College of Veterinary Medicine, South China Agricultural University, China
- China Animal Husbandry Group, China
Southern China has long been considered to be an epicenter of pandemic influenza viruses. The special environment, breeding mode, and lifestyle in southern China provides more chances for wild aquatic birds, domestic poultry, pigs and humans to be in contact. This creates the opportunity for interspecies transmission and generation of new influenza viruses.
In this study, we reported a novel reassortant H1N2 influenza virus from pigs in southern China. According to the phylogenetic trees and homology of the nucleotide sequence, the virus was conﬁrmed to be a novel triple-reassortant H1N2 virus containing genes from classical swine (PB2, PB1, HA, NP, and NS genes), triple-reassortant swine (PA and M genes) and recent human (NA gene) lineages.
It indicated that the novel reassortment virus among human and swine influenza viruses occurred in pigs in southern China.
The isolation of the novel reassortant H1N2 influenza viruses provides further evidence that pigs are ‘‘mixing vessels”, and swine influenza virus surveillance in southern China will provide important information about genetic evaluation and antigenic variation of swine influenza virus to formulate the prevention and control measures for the viruses.
The full (provisional) PDF of the report is available here.