#16,813
There are a lot of plausible candidate viruses for sparking the next global public health crisis (including Nipah, H5N6, H7Nx, MERS-CoV, and Virus X), but the one increasingly keeping Chinese and International scientists awake at night is the Eurasian Avian-Like (EA) Swine Influenza A(H1N1) Virus (and its reassortants) which is rife in China's pig population.
The alarm was first raised in late 2015 by Chen Hualan, director of China's National Avian Influenza Reference Laboratory, who was the lead author on a paper that identified a new, rising swine flu threat in China (see PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza).
EAH1N1 is a reassortant virus, with elements from H1N1 avian influenza, human H1N1pdm, and swine-origin influenza viruses. Despite sharing the same subtype designation as a currently circulating seasonal strain, it was genetically different enough to pose a genuine public health threat.
Here, we found that, after long-term evolution in pigs, the EAH1N1 SIVs have obtained the traits to cause a human influenza pandemic.
"Based on scientific analysis and comprehensive comparison of the main animal flu viruses: H1N1, H3N2, H5N1, H7N9, H9N2 and EAH1N1, we found the EAH1N1 is the one most likely to cause next human flu pandemic. We should attach great importance to the EAH1N1."
Since then, we've seen this virus continue to evolve, and spread, in China. While occasionally infecting humans, it has never taken off in the human population.
In 2019, we saw a number of studies on EAH1H1, including one that documented the virus in farmed mink in China (see Vet. MicroB.: Eurasian Avian-Like Swine Influenza A (H1N1) Virus from Mink in China).
And in 2020, in PNAS: Eurasian Avian-like H1N1 Swine Influenza Virus With Pandemic Potential In China, researchers reported greater than 10% seroprevalence for the EAH1N1 among swine workers tested, suggesting that EAH1N1 is gaining human infectivity.
These reports led to a number of `risk assessments' by public health agencies on EA H1N1 `G4', including:
The CDC's Responds to the PNAS EA H1N1 `G4' Swine Flu Study
ECDC Risk Assessment: Eurasian avian-like A(H1N1) swine influenza viruses
WHO Novel Flu Summary & Risk Assessment - July 2020
FAO/OIE/WHO Tripartite Statement on the Pandemic Risk of Swine Influenza
In early 2021, the CDC Selected Swine-Variant EA H1N1 Virus For The Top Of Their IRAT List of novel flu viruses with pandemic potential.
All of which brings us to a new dispatch, published yesterday in the CDC's EID Journal, that describes a growing number of EA H1N1 Swine influenza viruses (including a new H3N1 reassortant) with pandemic potential in China.
I've only posted the link, abstract, and some highlights from the report, so you'll want to hit the link and read it in its entirety. I'll have a postscript when you return.
Dispatch
Abstract
During 2018–2020, we isolated 32 Eurasian avian-like swine influenza A(H1N1) viruses and their reassortant viruses from pigs in China. Genomic testing identified a novel reassortant H3N1 virus, which emerged in late 2020. Derived from G4 Eurasian H1N1 and H3N2 swine influenza viruses. This virus poses a risk for zoonotic infection.
(SNIP)
Of note, in late 2020, we detected the H3N1 swine IAVs in 6 isolates (all from Zhejiang Province), indicating that this is a novel emerging recombinant genotype. Phylogenetic analyses demonstrated that the 6 novel H3N1 reassortant swine IAVs contained NA genes from the EA H1N1; PB2, PB1, PA, NP, and M genes from pH1N1; and NS genes from TRIG swine lineages. This combination is similar to the potentially pandemic G4 viruses except for the HA genes, suggesting that the emergence of novel H3N1 reassortant swine IAVs was a natural reassortant event that derived from G4 and H3N2 swine IAVs.
(SNIP)
Conclusions
Because of their susceptibility to avian, swine, and human IAVs, pigs are regarded as a mixing vessel for generating novel reassortant influenza viruses capable of replicating and spreading among humans (9,10). Implications for human health reinforce the importance of continuous surveillance of swine IAVs in the pig population. China has the most varied swine influenza virus ecosystem in the world and different subtypes simultaneously circulate among pigs (11,12). The emergence of potentially pandemic G4 EA H1N1 virus has increased the chances of reassortment with enzootic swine IAVs and the subsequential emergence of novel reassortant swine IAVs.
We isolated 6 EA H1N1 swine viruses and 26 reassortant EA H1N1 and H3N1 swine viruses in this study. Analysis results indicated that the reassortment of gene segments between EA H1N1 swine viruses and other enzootic swine viruses occurred frequently, and the reassortant swine viruses became established among the sampled pig population. Previous studies have reported several cases of human disease from EA H1N1 swine IAV or its reassortant viruses in Europe and China (13–15).
Our study, based on swine epidemiologic data from China, demonstrates that EA H1N1 swine influenza virus and its reassortant viruses circulate in swine populations and pose potential threats to human health. Furthermore, we isolated and documented the genetic evolution of novel reassortant H3N1 viruses between potentially pandemic G4 EA H1N1 and H3N2 swine IAVs. These findings highlight the need for surveillance for novel H3N1 viruses in swine and human populations to enable early interventions to avert outbreaks and protect animal and human health.
Dr. Wang is a PhD student at the Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, China. His primary research interests include the epidemiology and pathogenic mechanisms of influenza viruses.
The assumption is that H1, H2, and H3 viruses of swine or avian origin likely have a smaller `leap' to adapt to humans than do the strictly avian H5 and H7 subtypes.
While it is entirely possible we could be blindsided by another coronavirus, Nipah, or an H5 or H7 avian virus - if you want to play the odds - the next pandemic will more than likely come from a reassortant H1, H2, or H3 virus.
And while that could emerge from anywhere, right now China's EA H1N1 appears to be the front runner in the pandemic sweepstakes.
