Saturday, August 20, 2016

J. Virology: Introduction, Reassortment and Persistence of Diverse Influenza A Viruses in Antarctica

mBio S1 Supplemental – Global Flyways


A little over two years ago, in mBio: Evolutionarily Distinct H11N2 Avian Flu Found In Antarctica, we looked at the discovery of an avian  H11N2 virus among a small number of samples (n=8) collected from roughly 300 Adélie penguins inhabiting isolated Admiralty Bay and Rada Covadonga on the Antarctica Peninsula.

While distinct from other flu viruses seen around the globe, two of its gene segments shared common ancestry with South American AIVs, while the six remaining genes shared ancestry with either North American avian or equine viruses (H3N2).

Particularly interesting, molecular clock analysis suggested that this virus had been cut off from other flu viruses - evolving on its own - for between 49 and 80 years.

The Molecular Clock Hypothesis (MCH) proposes the speed of evolutionary change in different organisms is reasonably constant, can be measured, and can be used to extrapolate (roughly) how long it has been since two or more related organisms diverged from a common ancestor.

What is called their tMRCA (Time To Most Recent Common Ancestor).
 The big problem with molecular clock analysis has been calibration, as individual species mutate at different rates. Fortunately, in recent years scientists have gotten much better at refining these numbers, and so tMRCA's use is increasing.

This week the authors of the mBio study are back - this time in the Journal of Virology - with a follow up report that not only revisits H11N2, but also announces the new detection of a recently arrived H5N5 virus.   

The full open access report can be downloaded from the link below. 

Evidence for the introduction, reassortment and persistence of diverse influenza A viruses in Antarctica.

Hurt AC1, Su YC2, Aban M3, Peck H3, Lau H3, Baas C3, Deng YM3, Spirason N3, Ellström P4, Hernandez J5, Olsen B6, Barr IG3, Vijaykrishna D2, Gonzalez-Acuna D7.


Avian influenza virus (AIV) surveillance in Antarctica during 2013 revealed the prevalence of evolutionarily distinct influenza viruses of H11N2 subtype in Adélie penguins. Here we present results from the continued surveillance of AIV on the Antarctic Peninsula during 2014 and 2015. In addition to the continued detection of H11 subtype viruses during 2014 in a snowy sheathbill, we isolated a novel H5N5 subtype virus during 2015 in a chinstrap penguin. 

Gene sequencing and phylogenetic analysis revealed that the H11 virus detected in 2014 had a >99.1% nucleotide similarity to the H11N2 viruses isolated in 2013, suggesting continued prevalence of this virus over multiple years in Antarctica.

However, phylogenetic analysis of the H5N5 virus showed that their genome segments were recently introduced into the continent, except for the NP gene that was similar to that in the endemic H11N2 viruses. 

Our analysis indicates geographically diverse origins for the H5N5 virus genes; with the majority of its genome segments derived from North American lineage viruses, but the neuraminidase gene derived from a Eurasian lineage virus. 

In summary, we show the persistence of AIV lineages over multiple years in Antarctica; recent introduction of gene segments from diverse regions; and reassortment between different AIV lineages in Antarctica, which together, significantly increases our understanding of AIV ecology in this fragile and pristine environment.


Analysis of avian influenza viruses (AIVs) detected in Antarctica reveals both the relatively recent introduction of an H5N5 AIV predominantly of North American-like origin, as well as the persistence of an evolutionarily divergent H11 AIV. These data demonstrate that the flow of viruses from North America may be more common than initially thought, and that once introduced, these AIVs have the potential to be maintained within Antarctica. 

The future introduction of AIVs from North America into the Antarctic Peninsula is of particular concern given that highly pathogenic H5Nx viruses have recently been circulating amongst wild birds in parts of Canada and the Unites States following the movement of these viruses from Eurasia via migratory birds. The introduction of a highly pathogenic influenza virus into penguin colonies within Antarctica might have devastating consequences.

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