#14,514
Ten years ago we were still at the peak of the 2009 H1N1 swine-origin flu pandemic, and while we often see several decades between pandemics (1918 to 1957, or 1968 to 2009) - as the ECDC graphic above illustrates - sometimes those gaps are considerably shorter.
- 11 years between the 1889 Russian flu and the 1900 Old Hong Kong Flu
- 11 years between the 1957 H2N2 pandemic and the 1968 H3N2 Hong Kong flu
- And just 9 years later - in 1977 - H1N1 re-emerged after a 20 years absence
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| Credit Pandemic Influenza's 500th Anniversary |
And while we only have solid virological data going back to early in the 20th centruy, what evidence we do have suggests that all human influenza pandemics going back to the late 1800s have come from H1, H2, or H3 viruses (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?).
The progression of human influenza pandemics over the past 130 years appears to have been H2, H3, H1, H2, H3, H1, H1 . . .Although the next pandemic could break this repeating pattern - and come from an exotic avian H5, H7, or H10 virus - it makes sense to keep a close eye on the known repeat offenders.
While another H1 or H3 virus might emerge next (as happened in 2009), the repeating HA type that has been absent the longest is H2, and some researchers have suggested we are overdue for an H2 pandemic (see J.I.D.: Population Serologic Immunity To H2N2 For Pandemic Risk Assessment).
H2N2 sparked the Asian Flu pandemic of 1957, and reigned as the sole circulating human influenza A virus until 1968, when it was supplanted by H3N2 (now the longest known continuously circulating influenza subtype).But H2 flu viruses in the wild are - comparatively speaking - fairly rare. We see a good many H1 and H3 viruses in both pigs and birds, but H2 viruses are primarily found in Mallards, and only rarely in other species.
Over the past dozen years we've seen a handful of H2 flu viruses pop up around the world in a variety of mammalian and avian hosts.
- In 2017, in H2N2: Everything Old Is Flu Again, we saw a study published in The Journal Of Veterinary Medical Science, which detailed the finding of H2N2 in Siberian Muskrats. (see Genetic characterization of an H2N2 influenza virus isolated from a muskrat in Western Siberia).
- In 2016's A Novel Reassortant H2N8 In China, described an H2N8 avian flu virus was isolated from a domestic duck in Zhejiang Province, Eastern China, in 2013.
- In 2012, a PLoS One article (Recently Emerged Swine Influenza A Virus (H2N3) Causes Severe Pneumonia in Cynomolgus Macaques) found this swine H2N3 produced greater pathogenicity in a non-human primate than did the human H2N2 virus (see entry below).
- In 2006 and early 2007, a reassorted H2N3 subtype was detected in pigs on two different Missouri farms, which was the first known appearance of an H2 virus in a mammal since it was supplanted by the H3N2 virus in 1968 (see CIDRAP On Mutated Swine Flu Virus).
It is also worth noting that the LPAI H7N9 virus - which emerged in China in 2013, and has subsequently risen to the top of our pandemic watch list (see CDC IRAT ratings) - appears to have acquired its NA gene segment from either wild avian H2N9 and/or H11N9 influenza viruses.
You'll the abstract and some excerpts from today's article below, but you'll want to follow the link to read it in its entirety.
Viruses 2019, 11(11), 1046; https://doi.org/10.3390/v11111046
Article
Molecular Characterization of a Novel Avian Influenza A (H2N9) Strain Isolated from Wild Duck in Korea in 2018
by Seon-Ju Yeo 1,†, Duc-Duong Than 1,†, Hong-Seog Park 2, Haan Woo Sung 3,* and Hyun Park 1,*
Received: 25 October 2019 / Accepted: 6 November 2019 / Published: 10 November 2019
Abstract:
A novel avian influenza virus (A/wild duck/Korea/K102/2018) (H2N9) was isolated from wild birds in South Korea in 2018, and phylogenetic and molecular analyses were conducted on complete gene sequences obtained by next-generation sequencing.
Phylogenetic analysis indicated that the hemagglutinin (HA) and neuraminidase (NA) genes of the A/wild duck/Korea/K102/2018 (H2N9) virus belonged to the Eurasian countries, whereas other internal genes (polymerase basic protein 1 (PB1), PB2, nucleoprotein (NP), polymerase acidic protein (PA), matrix protein (M), and non-structural protein (NS)) belonged to the East Asian countries.
A monobasic amino acid (PQIEPR/GLF) at the HA cleavage site, E627 in the PB2 gene, and no deletion of the stalk region in the NA gene indicated that the A/wild duck/Korea/K102/2018 (H2N9) isolate was a typical low pathogenicity avian influenza (LPAI). Nucleotide sequence similarity analysis of HA revealed that the highest homology (98.34%) is to that of A/duck/Mongolia/482/2015 (H2N3), and amino acid sequence of NA was closely related to that of A/duck/Bangladesh/8987/2010 (H10N9) (96.45%). In contrast, internal genes showed homology higher than 98% compared to those of other isolates derived from duck and wild birds of China or Japan in 2016–2018.
The newly isolated A/wild duck/Korea/K102/2018 (H2N9) strain is the first reported avian influenza virus in Korea, and may have evolved from multiple genotypes in wild birds and ducks in Mongolia, China, and Japan.
(SNIP)
The prevalence of H2 subtype AIV is much lower than that of other subtypes such as H5, H7, and H9, [6] but H2 influenza viruses are found in wild birds [7], swine [8], and humans. The Asian pandemic of H2N2 influenza A virus resulted from reassortment of previously circulating human H1N1 and avian H2N2 viruses from 1957 to 1968 [8].
In 2006, an H2N3 virus isolated from swine in the United States of America, belonging to the American AIV lineage, shared 84–85% similarity with the H2N2 viruses of the 1957 influenza pandemic [9,10]. In wild waterfowl birds, the H2 subtype was mainly identified in mallard ducks in comparison to other subtypes [7,11,12].
Based on three patients infected by human H7N9, the constructed phylogenetic trees of NA genes showed H7N9, H2N9, or H11N9 as its origin. However, the Korean H7 subtype was suggested as the origin of highly pathogenic avian influenza (HPAI) H7N9 2013 [13]. H7N9 AIV has all three of its genes reasserted: hemagglutinin (HA) gene derived from H7N3, NA gene potentially from H7N9, H2N9, or H11N9 and six internal genes derived from H9N2 viruses [13].
Furthermore, the pandemic human H2N2 subtype (1957) originated upon reassortment between a previously circulating seasonal human A/H1N1 virus and an avian A/H2N2 virus [14].
(Continue . . . )Therefore, continuous surveillance of H2 subtype AIV in Korea is imperative.
In 2012, in H2N2: What Went Around, Could Come Around Again, we looked at a study conducted by scientists working at St. Jude Children's Research Hospital - published in the Journal of Virology - that concluded that H2N2 could well pose a threat to humanity once again.
A press release on this research warned:
1950s pandemic influenza virus remains a health threat, particularly to those under 50Nearly 8 years later, the pool of people without prior exposure to H2N2 has increased, and as of 2017 roughly 86% of the world's population hadn't been born when H2N2 last circulated (1968) as a human influenza virus.
St. Jude Children's Research Hospital scientists report that avian H2N2 influenza A viruses related to 1957-1958 pandemic infect human cells and spread among ferrets; may aid identification of emerging threats.
While H7N9 or H5N6 might produce a much higher mortality rate, H2 viruses have a long track record of successfully sparking human pandemics, making it a subtype definitely worth watching.
