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Influenza strains Venn diagram

Explore the interactive influenza Venn diagram to learn more about the various influenza strains that impact various species and humans.

H1N1

H1N1

Swine influenza (swine flu) is a respiratory disease of pigs caused by type A influenza viruses that regularly cause outbreaks of influenza in pigs. Swine flu viruses can cause high levels of illness in swine herds, but usually cause few deaths.(1)
H1N2

H1N2

1980: The first A(H1N2) virus reported in swine was in Japan. This was a classical swine A(H1N1) virus that had gained the neuraminidase (NA) from human A(H3N2) viruses.(2)
2012: In the United States, an A(H1N2) virus was transmitted to humans from swine. Australia recorded its first H1N2 subtype infection among swine.(2)
H2N2

H2N2

Caused the Asian pandemic of 1957 and then disappeared from the human population 10 years later. However, H2N2 continues to circulate in the avian reservoir and is coming into closer proximity to susceptible human populations.(4)
H3N2

H3N2

July 2011: Influenza A(H3N2) variant viruses were first detected in people. During 2011, 12 human infections with A(H3N2) were detected. The viruses were first identified in pigs in the US in 2010.(6)
H3N3

H3N3

Internal genes of H3N3 might be derived from viruses of waterfowl origin (mainly ducks) in North America (Alaska) and East Asia (Japan and the Republic of Korea).(7)
H3N8

H3N8

First detected in wild birds in the 1960s and has been detected in other animals.(8) April 2022: The first human infection with avian influenza virus (H3N8) was reported. The case was in a four-year-old boy whose family reared chickens and silky fowls in Henan Province, China. (9)
H4N5

H4N5

1982–1983: H4N5 influenza A viruses were recovered from harbour seals dying of viral pneumonia on the New England coast.(10)
H4N6

H4N6

1999: First report of interspecies transmission of an avian H4 influenza virus to domestic pigs under natural conditions.(11) 2009: In a live-bird market in Bangkok, Thailand, out of 970 samples collected, influenza A virus, subtype H4N6 (n = 2), were isolated from healthy Muscovy ducks. (12)
H5N1

H5N1

The avian influenza virus A(H5N1) emerged in 1996. It was first identified in southern China and Hong Kong.(13) 2023: Europe has been experiencing a large epidemic of A(H5N1) viruses in birds, with outbreaks reported in domestic birds, wild birds, and mammals across 24 countries. Outbreaks in wild and domestic birds continue to be reported through May 2023. (14)
H5N2

H5N2

2003–2012: Sporadic activity by H5N2 influenza viruses has been observed in chickens in Taiwan.(15)
H5N3

H5N3

Detected in birds in Quebec and British Columbia in 2005.(16)
H5N9

H5N9

Detected in birds in Quebec and British Columbia in 2005.(16) 2015: Outbreaks reported in France with six regions affected. (17)
H5N6

H5N6

H5-subtype viruses evolved into multiple distinct subclades, among which 2.3.4.4 has become dominant in China, and H5N6 viruses of this subclade led to an apparent increase in human infections in 2021 and 2022.(18)
H6N1

H6N1

2013: Taiwan reported the first known human infection with LPAI A(H6N1) virus.(21) Low pathogenic avian influenza A(H6) virus outbreaks in birds are not internationally reportable, therefore, its true prevalence is unknown. However, low pathogenic avian influenza A(H6) viruses have been identified in various species of wild waterfowl and domestic poultry in Eurasia and the Americas. (21)
H6N2

H6N2

Low pathogenic avian influenza A(H6) virus outbreaks in birds are not internationally reportable, therefore, its true prevalence is unknown. However, low pathogenic avian influenza A(H6) viruses have been identified in various species of wild waterfowl and domestic poultry in Eurasia and the Americas.(21)
H7N3

H7N3

In 2012, there were three outbreaks in an area with high poultry density in Mexico.(22) In 2020, a low-pathogenicity event occurred on commercial turkey farms in North Carolina and South Carolina, USA. (23)
H7N7

H7N7

Highly pathogenic avian influenza A(H7N7) virus infections have been reported in more than 90 people, since the first human infection was identified in the US in 1959; although that infection was associated with hepatitis, most infections have been associated with conjunctivitis.(24)
H7N9

H7N9

Up until the fifth wave (2016–2017), avian A(H7N9) was considered low pathogenic; however, during the fifth wave, WHO confirmed evidence of strains of highly pathogenic avian influenza A(H7N9) circulating in birds in China, together with subsequent human infections.(25)
H7N2

H7N2

In 2016, one human infection was confirmed in a cat shelter worker in New York City, who had prolonged contact with infected cats. Previously, there have been two human infections with similar H7N2 occurring in 2002 and 2003. One of these infections was associated with exposure to infected poultry.(26)
H9N2

H9N2

More than 100 human cases of H9N2 avian influenza virus have been reported as of July 2022, including more than 50 cases after the outbreak of COVID-19.(27)
H10N7

H10N7

Originated in aquatic birds but can cause localised outbreaks (rather than permanent lineages) in other animals.(28)
 
Viral infections were reported in a small number of people with conjunctivitis or mild upper respiratory tract symptoms in Egypt in 2004 and Australia in 2010.(24)
H10N8

H10N8

Three cases in Nanchang, Jiangxi, China, between November 2013 and February 2014. The virus isolated from the initial patient was a reassortant virus, with its internal and surface genes derived from the H9N2 viruses enzootic in chickens, ducks and wild birds. Market chickens were the likely source for those infected patients.(29)
H13N2 / H13N9

H13N2 &
H13N9

H13 subtype detected in less than 5 out of 20 years of surveillance (<25%).(30) H13N2 originates in aquatic birds but can cause localised outbreaks (rather than permanent lineages) in other animals.(28)
H17

H17

2012: Discovered in bats via isolation by next generation sequencing (winged mammals, as opposed to winged birds).(31)
H18

H18

Detected in 2010 in New World bats in Peru.(32)
H11

H11

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H11 is intermediately detected in mallards.(30)
H8

H8

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H8 is intermediately detected in mallards.(30)
H12

H12

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H12 is intermediately detected in mallards.(30)
H14

H14

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H14 is intermediately detected in mallards.(30)
H15

H15

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H15 is intermediately detected in mallards.(30)
H16

H16

Subtype detected in 5–14 years out of a 20-year surveillance (25% to 75%). Surveillance in Eurasia indicates H16 is intermediately detected in mallards.(30)
H5N8

H5N8

Since 2014: Circulating in European bird populations, causing large outbreaks and affected several million birds and poultry.(19) 2020–2021: Highly pathogenic avian influenza H5N8 (clade 2.3.4.4b) virus detected in dust samples from poultry farms during a large epizootic in France. (20)
B

Influenza B

Influenza B viruses are not classified into subtypes but can be broken down into lineages. Currently circulating influenza type B viruses belong to either B/Yamagata or B/Victoria lineage.(33)
C

Influenza C

Influenza C virus infections generally cause mild illness and are not thought to cause human epidemics; therefore, it is not of public health importance.(33)

References:

  1. CDC. Information on Swine/Variant Influenza [Internet]. 22 March 2024. Available from: https://www.cdc.gov/swine-flu/about/index.html [Accessed October 2024]
  2. Komadina N, McVernon J, Hall R, Leder K. A Historical Perspective of Influenza A(H1N2) Virus. Emerg Infect Dis. 2014;20(1):6–12. https://doi.org/10.3201/eid2001.121848
  3. Dierauf L, Frances M.D. Gulland. CRC Handbook of Marine Mammal Medicine. CRC Press; 2001.
  4. Schäffr JR, Kawaoka Y, Bean WJ, et al. Origin of the Pandemic 1957 H2 Influenza A Virus and the Persistence of Its Possible Progenitors in the Avian Reservoir. Virology. 1993;194(2):781–8. https://doi.org/10.1006/viro.1993.1319
  5. Stadejek W, Chiers K, Van Reeth K. Infectivity and Transmissibility of an Avian H3N1 Influenza Virus in Pigs. Vet Res. 2023;54(4). https://doi.org/10.1186/s13567-022-01133-x
  6. Jhung MA, Epperson S, Biggerstaff M, et al. Clin Infect Dis. 2013;57(12):1703–12. https://doi.org/10.1093/cid/cit649
  7. Yang J, Yang L, Zhu W, Wang D, Shu Y. Epidemiological and Genetic Characteristics of the H3 Subtype Avian Influenza Viruses in China. China CDC Weekly. 2021;3(44):929–36. https://doi.org/10.46234/ccdcw2021.225
  8. CDC. Human Infection with Avian Influenza A(H3N8) Virus Reported by China [Internet]. 29 April 2024. Available from: https://www.cdc.gov/bird-flu/spotlights/avian-influenza-h3n8-china.html [Accessed October 2024]
  9. Yang J, Zhang Y, Yang L, et al. Evolution of Avian Influenza Virus (H3) with Spillover into Humans, China. Emerg Infect Dis. 2023;29(6):1191–201. https://doi.org/10.3201/eid2906.221786
  10. Horimoto T, Kawaoka Y. Pandemic Threat Posed by Avian Influenza A Viruses. Clin Microbiol Rev. 2001;14(1):129–49. https://doi.org/10.1128/CMR.14.1.129-149.2001
  11. Karasin AI, Brown IH, Carman S, Olsen CW. Isolation and Characterization of H4N6 Avian Influenza Viruses from Pigs with Pneumonia in Canada. J Virol. 2000;74(19):9322–7. https://doi.org/10.1128/jvi.74.19.9322-9327.2000
  12. Wisedchanwet T, Wongphatcharachai M, Boonyapisitsopa S, et al. Genetic Characterization of Avian Influenza Subtype H4N6 and H4N9 from Live Bird Market, Thailand. Virol J. 2011;8:131. https://doi.org/10.1186/1743-422X-8-131
  13. ECDC. Facts About Avian Influenza in Humans [Internet]. Last updated 08 February 2023. Available from: https://www.ecdc.europa.eu/en/avian-influenza-humans/facts [Accessed October 2024]
  14. WHO. Avian Influenza A(H5N1) – United Kingdom of Great Britain and Northern Ireland [Internet]. 20 May 2023. Available from: https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON468 [Accessed October 2024]
  15. Lee CC, Zhu H, Huang PY, et al. Emergence and Evolution of Avian H5N2 Influenza Viruses in Chickens in Taiwan. J Virol. 2014;88(10):5677–86. https://doi.org/10.1128/JVI.00139-14 [Epub 12 Mar 2014]
  16. NBC News. Non-Virulent Avian Flu Strain Found in BC Duck [Internet]. 20 November 2005. Available from: https://www.nbcnews.com/id/wbna10128209 [Accessed October 2024]
  17. The Poultry Site. French Bird Flu Outbreak Total Passes Fifty [Internet]. 22 December 2015. Available at: https://www.thepoultrysite.com/news/2015/12/french-bird-flu-outbreak-total-passes-fifty [Accessed October 2024]
  18. ‌Zhang J, Ye H, Liu Y, Liao M, Qi W. Resurgence of H5N6 Avian Influenza Virus in 2021 Poses New Threat to Public Health. Lancet Microbe. 2022;3(8):e558. https://doi.org/10.1016/S2666-5247(22)00148-3
  19. ECDC. Threat Assessment Brief: First Identification of Human Cases of Avian Influenza A(H5N8) Infection [Internet]. 24 February 2021. Available from: https://www.ecdc.europa.eu/en/publications-data/threat-assessment-first-human-cases-avian-influenza-h5n8 [Accessed October 2024]
  20. Filaire F, Lebre L, Foret-Lucas C, et al. Highly Pathogenic Avian Influenza A(H5N8) Clade 2.3.4.4b Virus in Dust Samples from Poultry Farms, France, 2021. Emerg Infect Dis. 2022;28(7):1446–50. https://doi.org/10.3201/eid2807.212247 [Epub 31 May 2022]
  21. CDC. Avian Influenza Type A Viruses [Internet]. 30 May 2024. Available from: https://www.cdc.gov/bird-flu/about/index.html [Accessed October 2024]
  22. Food and Agriculture Organization of the United Nations. Highly Pathogenic Avian Influenza in Mexico (H7N3) – A Significant Threat to Poultry Production Not to be Underestimated. EMPRES WATCH. 2012;26-August. Rome. Available from: https://www.fao.org/4/an395e/an395e.pdf [Accessed October 2024]
  23. Youk S, Lee DH, Killian ML, et al. Highly Pathogenic Avian Influenza A(H7N3) Virus in Poultry, United States, 2020. Emerg Infect Dis. 2020;26(12):2966–9. https://doi.org/10.3201/eid2612.202790
  24. CDC. Reported Human Infections with Avian Influenza A Viruses | Avian Influenza (Flu) [Internet]. 01 February 2024.. Available from: https://www.cdc.gov/bird-flu/php/avian-flu-summary/reported-human-infections.html [Accessed October 2024]
  25. GOV.UK. Risk Assessment of Avian Influenza A(H7N9) – eighth update [Internet]. Updated 08 January 2020. Available from: https://www.gov.uk/government/publications/avian-influenza-a-h7n9-public-health-england-risk-assessment/risk-assessment-of-avian-influenza-ah7n9-sixth-update [Accessed October 2024]
  26. CDC Archive. Avian Influenza A (H7N2) in Cats in Animal Shelters in NY; One Human Infection [Internet]. 22 December 2016. Available from: https://archive.cdc.gov/#/details?url=https://www.cdc.gov/flu/spotlights/avian-influenza-cats.html [Accessed October 2024]
  27. Bi Y, Li J, Shi W. The Time is Now: A Call to Contain H9N2 Avian Influenza Viruses. Lancet Microbe. 2022;3(11):e804–5. https://doi.org/10.1016/S2666-5247(22)00232-4
  28. World Health Organization. WHO Manual on Animal Influenza Diagnosis and Surveillance. 2002. Available from: https://www.chinacdc.cn/jkzt/crb/gjfd/zl/rgrgzbxqlg/jszl_2207/200510/P02005101124362428831469904020905865.pdf [Accessed October 2024]
  29. Ma C, Lam TT, Chai Y, et al. Emergence and Evolution of H10 Subtype Influenza Viruses in Poultry in China. J Virol. 2015;89(7):3534–41. https://doi.org/10.1128/JVI.03167-14 [Epub 14 January 2015]
  30. Verhagen JH, Eriksson P, Leijten L, et al. Host Range of Influenza A Virus H1 to H16 in Eurasian Ducks Based on Tissue and Receptor Binding Studies. J Virol. 2021;95(6):e01873-20 [Epub 23 December 2020] https://doi.org/10.1128/JVI.01873-20
  31. Wu Y, Wu Y, Tefsen B, Shi Y, Gao GF. Bat-Derived Influenza-Like Viruses H17N10 and H18N11. Trends Microbiol. 2014;22(4):183–91. https://doi.org/10.1016/j.tim.2014.01.010 [Epub 26 February 2014]
  32. Yang W, Schountz T, Ma W. Bat Influenza Viruses: Current Status and Perspective. Viruses. 2021;13(4):547. https://doi.org/10.3390/v13040547
  33. WHO. Influenza (Seasonal) [Internet]. 03 October 2023. Available from: https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)#:~:text=Most%20people%20recover%20from%20fever [Accessed October 2024]

GBR-FLU-24-0092 | October 2024

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