Avian Flu Diary: JID: Evolutionary Dynamics Of Influenza A Viruses In US Exhibition Swine

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Although bird flu has captured most of our attention over the past year, scientists are abundantly aware of the potential for seeing novel swine-origin influenza viruses emerge as well.

Just last week in Live Markets & Novel Flu Risks In The United States, we looked at some of the zoonotic exposure risks and two weeks ago in Novel (H3N2v) Flu Case Reported In Minnesota, we saw the latest reported human infection with a swine-variant virus.

Swine are considered excellent `mixing vessels’ for influenza, as they are susceptible to a wide variety (swine, human, avian) of flu strains, they may be co-infected by more than one virus at a time, and they not only have ample contact with other pigs, but with humans as well.

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.

The 2009 H1N1 pandemic evolved from numerous reassortments in swine over a period of years, finally jumping species when it had become well enough adapted to human physiology.

Here in North America we’ve been watching the evolution of several swine variant viruses (H1N1v, H1N2v, H3N2v) over the past few years, all of which have reassorted with - and picked up the M gene segment from – the 2009 H1N1 virus (see Keeping Our Eyes On The Prize Pig).

All of which serves as prelude to a new study, and an accompanying editorial, published today in the Journal of Infectious Diseases that looks at the ongoing evolution of swine origin influenza viruses and the threats they pose to human health.

First the abstract (slightly reformatted for readability) to the study (a preliminary PDF version of the whole study is available).

Evolutionary dynamics of influenza A viruses in US exhibition swine

Martha I. Nelson 1, David E. Wentworth 2,∧, Suman R. Das 2, Srinand Sreevatsan 3, Mary L. Killian 4, Jacqueline M. Nolting 5, Richard D. Slemons 5 and Andrew S. Bowman 5,*

Abstract

The role of exhibition swine in influenza A virus (IAVs) transmission was recently demonstrated by over 300 human infections of H3N2v viruses while attending agricultural fairs. Through active IAV surveillance in US exhibition swine and whole-genome sequencing of 380 isolates, we demonstrate that exhibition swine are actively involved in the evolution of IAVs, including zoonotic strains.

First, frequent introduction of IAVs from commercial swine populations provides new genetic diversity in exhibition pigs each year locally.
Second, genomic reassortment between viruses co-circulating in exhibition swine increases viral diversity.
Third, viral migration between exhibition swine in neighboring states demonstrates that movements of exhibition pigs contributes to the spread of genetic diversity.

The unexpected frequency of viral exchange between commercial and exhibition swine raises questions about the understudied interface between these populations. Overall, the complexity of viral evolution in exhibition swine indicates novel viruses are likely to continually re-emerge, presenting threats to humans.

(Continue . . . )

JID also published an accompanying editorial by Tiana Baranovich and Justin Bahl called Influenza A Virus diversity and transmission in exhibition swine (full text available) that warns `The manners in which these H3N2v viruses have become established in exhibition swine suggest that exhibition swine should be considered a unique reservoir for influenza viruses with pandemic potential’

For more on swine-origin influenza viruses and the potential threats they pose, you may wish to revisit:

EID Journal: Influenza A Viruses of Human Origin in Swine, Brazil

USDA IAV-S Surveillance Program Detects Novel H3N1 In US Swine

Study: Reassortants of H1N1pdm & Swine H1 & H3 Viruses in Japan

EID Journal: H3N2v Swine To Human Transmission At Agricultural Fairs – 2012