Study: Novel & Variant Swine Influenzas In Korean Pigs

Since pigs can be infected by more than one flu virus at the same time, it is possible for two viruses to swap genetic material (reassort), resulting in a new hybrid strain.

# 7621

 

We’ve more evidence today that nature’s laboratory continues to produce new, and possibly troublesome, flu viruses from a report that appeared yesterday in the journal Influenza and other Respiratory Viruses.

 

Swine are considered excellent `mixing vessels’ for influenza because they are susceptible to a variety of human, swine, and avian strains of flu.  As such, they have the opportunities to be co-infected by two different strains simultaneously.

 

The most common swine flu viruses are H1N1, H1N2, H3N1, H3N2, and H2N3. These viruses, when they jump to humans, are called variant viruses (e.g. H3N2v).

 

Starting in 2011, the H1N1v virus was found to have acquired the M (matrix) gene from the 2009 H1N1 pandemic virus. Since then, this M gene has been showing up regularly in all three swine variant viruses (H1N1v, H1N2v, H3N2v).

 

The CDC has speculated that `This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’ – CDC HAN 2012

 

The concern with these variant swine flu infections, as with any novel flu, is that each new human exposure provides the virus another opportunity to better adapt to human physiology.

 

All of which brings us to a new study that has not only found the first evidence of H3N2v in swine outside of the United States, but also finds a new H3N1 reassortant virus that appears to transmit well among ferrets and replicate well in human cell lines.

 

Excerpts from the study’s abstract follow, after which I’ll return with more:

 

Emergence of H3N2pM-like and novel reassortant H3N1 swine viruses possessing segments derived from the A (H1N1)pdm09 influenza virus, Korea

Philippe Noriel Q. Pascua, Gyo-Jin Lim, Hyeok-il Kwon, Su-Jin Park, Eun-Ha Kim, Min-Suk Song, Chul Joong Kim, Young-Ki Choi

Article first published online: 30 AUG 2013

Result

We identified reassortant H3N2 (H3N2pM-like) and H3N1 swine viruses containing A(H1N1)pdm09-like segments in Korean pigs that are genetically closely related to strains recently detected in pigs and humans in North America.

 

Although the H3N2pM-like and novel H3N1 reassortants demonstrated efficient replication in mice and ferrets, all the H3N1 strains exhibited growth advantage over the representative H3N2pM-like virus in human airway cells.

 

Interestingly, A/swine/Korea/CY02-07/2012(H3N1) and A/swine/Korea/CY03-13/2012(H3N1) reassortants were more readily transmitted to respiratory-droplet-contact ferrets compared with the H3N2pM-like (A/swine/Korea/CY02-10/2012) isolate. Furthermore, serologic evaluation showed poor antigenicity to contemporary reference human seasonal H3N2 vaccine strains.

Conclusions

We report here for the first time the isolation of H3N2pM-like viruses outside North America and of novel reassortant swine H3N1 viruses with A(H1N1)pdm09-derived genes. Apart from further complicating the genetic diversity of influenza A viruses circulating in domestic pigs, our data also indicate that these strains could potentially pose threat to public health asserting the need for continuous virus monitoring in these ecologically important hosts.

 

 

One of the biggest lessons learned from the past few years was that influenza viruses don’t always follow the script.

 

Not only did the last pandemic virus emerge from the `wrong’ species (pigs instead of birds), it came from the `wrong’ continent (North America instead of Asia) and from a completely unexpected lineage (H1N1).

 

While pigs have long been considered potential mixing vessels for influenza viruses, today that threat is taken more seriously than it was in the past. The continued evolution in swine viruses, particularly reassorting with `humanized’ strains like H1N1pdm, is of particular concern.

 

 

 

Undoubtedly, influenza reassortments happen all the time and mostly outside the view of scientists. Most are viral flashes in the pan, are unable to compete with more biologically fit flu viruses, and quickly disappear into the evolutionary dustbin.

 

But occasionally, the right genetic combination will be generated, and a new emerging virus is born.

 

All of which highlights the need for continual and enhanced surveillance of humans, livestock, and wild birds for emerging viral threats. Because it isn’t a question of if another pandemic will emerge.

 

It’s only a matter of when.