The Return of Influenza A(H2N2) Virus

Influenza viruses follow a distinct pattern and timeline: H2, H3, H1, H2, H3, H1, H1.
Influenza A(H2N2) viruses caused two pandemics (1898 and 1957), about 69 years apart;
Influenza A(H3Nx) viruses caused two pandemics (1900 and 1957), about 68 years apart;
Influenza A(H1N1) viruses caused two pandemics (1918 and 1977), about 59 years apart;
Then apparently out of sync, the novel Influenza A(H1N1) Virus reemerged in 2009.

If nature can be trusted (which it certainly cannot), the next potential pandemic could be cause by the return of Influenza A(H2N2) Virus.

In 2011, after the first shock over the 2009 H1N1 pandemic had finally died down, some researchers suggested it might make sense to add an H2N2 component to the seasonal vaccine to head off the `next' pandemic[1]. As could be predicted, nobody really took care of this futuristic idea.

Research from 2013 studied 22 H2N2 avian viruses collected from domestic poultry and wild aquatic birds between 1961 and 2008. The researchers found evidence that descendants of the Influenza A(H2N2) virus, that killed millions worldwide in the 1950s, still pose a threat to human health, particularly to those under 50[2].

So, Influenza A(H2N2) Virus still roams free in the wild and it was no real surpise when Russian scientists isolated a variant of Influenza A(H2N2) Virus in a muskrat (Ondatra zibethicus): A/muskrat/Russia/63/2014 (H2N2)[3].
Results suggest that interspecies transmission of Influenza A viruses from wild water birds to semiaquatic mammals occurs, facilitating the spread and evolution of Influenza A viruses in wetland areas of Western Siberia. At the moment this mammalian Influenza A(H2N2) Virus presents no evidence of virulence for humans or poultry. Thus, it may be a muskrat-adapted virus or a transient virus in the nasal cavity of muskrats. The researchers think that muskrats could serve as a new reservoir of Influenza A viruses, posing a potential risk to other animals in the food chain, including humans.

[1] Nabel et al: Vaccinate for the next H2N2 pandemic now in Nature - 2011
[2] Jones et al: Risk assessment of H2N2 influenza viruses from the avian reservoir in Journal of Virology – 2014
[3] Gulyaeva et al: Genetic characterization of an H2N2 influenza virus isolated from a muskrat in Western Siberia in Journal of Veterinary Medical Science - 2017

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