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Table of Contents
Year : 2021  |  Volume : 14  |  Issue : 3  |  Page : 97-98

Genotype 4 reassortant Eurasian avian-like H1N1 swine flu virus: An emerging public health challenge

1 Department of Community Medicine, Armed Forces Medical College, Pune, Maharashtra, India
2 Department of Zoology, Asutosh College (University of Calcutta), Kolkata, West Bengal, India
3 Department of Zoology, Dinabandhu Andrews College (University of Calcutta), Kolkata, West Bengal, India

Date of Submission10-Sep-2020
Date of Decision14-Dec-2020
Date of Acceptance07-Jan-2021
Date of Web Publication02-Feb-2021

Correspondence Address:
Rina Tilak
Department of Community Medicine, Armed Forces Medical College, Pune, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1995-7645.307531

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How to cite this article:
Tilak R, Bhattacharya S, Sinha S. Genotype 4 reassortant Eurasian avian-like H1N1 swine flu virus: An emerging public health challenge. Asian Pac J Trop Med 2021;14:97-8

How to cite this URL:
Tilak R, Bhattacharya S, Sinha S. Genotype 4 reassortant Eurasian avian-like H1N1 swine flu virus: An emerging public health challenge. Asian Pac J Trop Med [serial online] 2021 [cited 2023 Jun 5];14:97-8. Available from:

  1. Introduction Top

Influenza A viruses (IAV), an orthomyxovirus, is reportedly prevalent in a large number of avian species and mammals including humans, and poses immense public health challenge as a potential pandemic originator[1]. It has been reported that IAV and Eurasian avian-like (EA) lineage influenza viruses have been co-circulating in pigs for nearly two decades in the Asian continent[2]. Pigs are known to be maintenance hosts for EA H1N1 besides acting as ‘mixing bowls’, with the potential to harbor viral strains which can cause pandemics[3]. The deadly impact of the two H1N1 pandemics in the recent past viz. the much famed Spanish flu of 1918 and the 2009 swine flu[1] pandemic rankles the scientific fraternity and public health experts till date. One re-assortant strain of EA H1N1 namely genotype 4 (G4) reassortant Eurasian avian-like (EA) H1N1 (G4EA H1N1) has been reported to be present in pigs of certain provinces of China since the last decade. The detection of G4 EA H1N1 amongst personnel working in slaughterhouses in the swine industry in China[4] draws attention to the likely possibility of a G4 EA H1N1 pandemic in the near future, if not addressed well in time. The G4 EA H1N1 is known to possess characteristics that are considered favorable for its adaptation amongst humans[4]. Thus, the likelihood of a potential pandemic of G4 EA H1N1 in the near future has turned into a hot, yet dreaded topic of discussion amongst the skeptic scientific fraternity. In this context, this paper is an attempt to assess and analyze the possible public health challenges from G4 EA H1N1 and the requirement of forming country-specific strategies to combat the potential human transmission and outbreaks.

  2. IAV-a potent ‘pandemic originator’ Top

IAV is one of the most dynamic viruses and a proven ‘pandemic originator’ due to its capability of extensive re-assortment resulting in novel re-assortant viruses. The 2009 swine flu undisputedly heralded the era of re-assortant viruses. Unlike the majority of human swine influenza infections, this re-assortant virus was capable of continuous human-to-human transmission, resulting in a global pandemic[5]. As per WHO, the flu reportedly impacted more than 214 countries, making it the first global pandemic post the 1968 Hong Kong flu[6]. Similarly, another influenza virus re-assortant strain is G4 EA H1N1, commonly called the ‘G4 swine flu virus’. This ‘G4 swine flu virus’ is very similar to the 2009 ‘swine flu’-A/H1N1pdm09 which has been reported to be in circulation amongst pig populations in China with steadily increasing infectivity since 2016[4].

  3. Swine flu virus ‘G4 EA H1N1’ Top

The newly discovered G4 EA H1N1 virus is a cocktail of three lineages of influenza viruses, the H1N1 strain that caused the 2009 swine flu pandemic, the strains found in European and Asian birds and a North American H1N1 strain that has genes from human, pig and avian influenza viruses[4]. Although G4 EA H1N1 primarily affects pigs[7], yet recent evidence of its infection amongst humans has raised concerns[4]. To date, there is no evidence of human-to-human transmission, nonetheless, reports of pig populations in China being infected by G4 EA H1N1 [4] raise the likely chances of virus spillover to humans. Apprehensions have been raised by some investigators that G4 EA H1N1 may likely be transmitted between humans as it possesses “all the characteristics” including the binding ability to human-like SA 2, 6Gal receptor for adapting to humans[4]. As on date, G4 EA H1N1 qualifies to be listed in the second phase of the “WHO Pandemic Phase Descriptions”[8], since evidence for only animal-to-human transmission has been confirmed with 35 people being reported to be infected with the virus[4],[7]. Studies have also revealed that about 4% of the 230 people from the general population had antibodies to G4 viruses[7].

  4. Pigs as ‘mixing bowls’ for influenza viruses Top

Pigs are infamous for serving as hosts or “mixing bowls” for influenza viruses with pandemic potential by the creation of novel and potentially hazardous re-assortant viruses[3]. The presence of cellular receptors i.e. α-2,6-linked sialic acids (Sias) (humanlike receptors) and α-2,3-linked (Sias) (avian-like receptors) in the trachea of pig supports virus replication of both the avian as well as mammalian lineages[9]. Once the pigs get infected, the viruses tend to gain the adaptations essential for either maintaining the infection in pigs, thus acting as a reservoir for human infection, or allowing mutations necessary for transmission to humans, thereby leading to its establishment in human population[10]. Results of a recent study (2011-2018) on influenza virus surveillance amongst pig populations in China revealed the presence of G4 re-assortant EA H1N1 virus since the year 2016 onwards[4]. A high sero prevalence of 10.4% amongst swine workers indicates that the G4 EA H1N1 virus has acquired increased human infectivity which enhances the chances for the virus to adapt to humans.

  5. Need for country-specific ' influenza virus surveillance cells’ (IVSC) Top

In the light of the fact that the future is fraught with likely pandemics of influenza viruses spilling over from animals like bats, pigs, pangolin, etc. to humans causing Spanish flu or swine flu-like pandemics, we need to establish country-specific IVSC for early warning of novel virus activity. The most challenging aspect is the similar clinical presentation of all influenza viruses, which further strengthens the cause for establishing these surveillance cells. These IVSC's should continuously engage in monitoring for probable new influenza virus strains with outbreak potential. The warning from these cells will facilitate the implementation of preemptive measures to contain outbreaks at the local level and thus prevent transcontinental transmission and likely pandemics.

  6. Conclusions Top

The era of ‘influenza virus pandemics’ has undoubtedly dawned. The influenza virus pandemics are a real threat to human health especially given the origin of new re-assortant virus strains. The report of swine flu virus ‘G4 EA H1N1’ amongst pigs is a warning sign of a novel threat of a probable pandemic in waiting. Unfortunately, there is no evidence yet of immunity amongst the human population to this new G4 strain of the avian influenza virus. The currently available flu vaccines also show minimal promise of protection against the new ‘swine flu virus’ thereby necessitating the development of a new vaccine. Although the world is relentlessly engaged in waging a war against these highly potent biological entities, yet it tends to take us for a surprise each time with an outbreak by a more potent strain than before. These re-assortant viruses possess the capability of causing fresh pandemics, hitherto not known to humans. Any slackness of surveillance on this new emerging challenge may potentiate outbreaks of G4 EA H1N1.

Conflict of interest statement

The authors declare there is no conflict of interest.

Authors’ contributions

The conceptualization was done by R.T. The formal analysis and interpretation were done by R.T, S.B and S.S. The resource and writing-original draft preparation were carried out by R.T and S.S. The writing review and editing were performed by R.T and S.B. The supervision was done by R.T and S.B. The whole manuscript was read and approved by all authors.

  References Top

World Health Organization. Influenza (avian and other zoonotic), fact sheets 2018. [Online]. Available from: fact-sheets/detail/influenza-(avian-and-other-zoonotic). [Accessed on 11 August 2020].  Back to cited text no. 1
Chen Y, Zhang J, Qiao CL, Yang HL, Zhang Y, Xin XG, et al. Co-circulation of pandemic 2009 H1N1, classical swine H1N1 and avian-like swine H1N1 influenza viruses in pigs in China. Infect Genet Evol 2013; 13: 331-338.  Back to cited text no. 2
Yang H, Chen Y, Qiao C, He X, Zhou H, Sun Y, et al. Prevalence, genetics, and transmissibility in ferrets of Eurasian avian-like H1N1 swine influenza viruses. Proc Natl Acad Sci USA 2016; 113(2): 392-397.  Back to cited text no. 3
Sun H, Xiao Y, Liu J, Wang D, Li F, Wang C, et al. Prevalent Eurasian avian-like H1N1 swine influenza virus with 2009 pandemic viral genes facilitating human infection. Proc Natl Acad Sci USA 2020; 117(29): 17204-17210.  Back to cited text no. 4
York I, Donis RO. The 2009 pandemic influenza virus: Where did it come from, where is it now, and where is it going? Curr Top Microbiol Immunol 2013; 370: 241-257.  Back to cited text no. 5
WHO. World now at the start of 2009 influenza pandemic. Statement to the press by WHO Director General-Dr Margaret Chan. 2009. [Online]. Available from: h1n1_pandemic_phase6_20090611/en/. [Accessed on 11 August 2020].  Back to cited text no. 6
Centers for Disease Control and Prevention. CDC takes action to prepare againstG4swine flu viruses in China with pandemic potential. 2020. [Online]. Available from: cdc-prepare-swine-flu.html. [Accessed on 11 August 2020].  Back to cited text no. 7
World Health Organization. World pandemic phase descriptions and main actions by phase. 2020. [Online]. Available from: influenza/resources/documents/pandemic_phase_descriptions_and_ actions.pdf. [Accessed on 11th August 2020].  Back to cited text no. 8
Ito T, Suzuki Y, Mitnaul L, Vines A, Kida H, Kawaoka Y. Receptor specificity of influenza A viruses correlates with the agglutination of erythrocytes from different animal species. Virology 1997; 227(2): 493-499.  Back to cited text no. 9
Löndt BZ, Brookes SM, Nash BJ, Núñez A, Stagg DA, Brown IH. The infectivity of pandemic 2009 H1N1 and avian influenza viruses for pigs: An assessment by ex vivo respiratory tract organ culture. Influenza Other Respir Viruses 2013; 7(3): 393-402.  Back to cited text no. 10


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  In this article
1. Introduction
3. Swine flu vir...
6. Conclusions
2. IAV-a potent ...
4. Pigs as ̵...
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