Video:Influenza A virus subtype H5N1

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Influenza A virus subtype H5N1 can cause illness in humans and many other animal species.[1] A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza bird flu.[2]

Signs and symptoms

In general, humans who catch a humanized influenza A virus usually have symptoms that include fever, cough, sore throat, muscle aches, conjunctivitis, and, in severe cases, breathing problems and pneumonia that may be fatal.[3]

Subtype genetics 1

H5N1 is a subtype of the species Influenza A virus of the genus Alphainfluenzavirus of the family Orthomyxoviridae. Like all other influenza A subtypes, the H5N1 subtype is a RNA virus. It has a segmented genome of eight negative sense, single-strands of RNA, abbreviated as PB2, PB1, PA, HA, NP, NA, MP and NS.[1][4]

Subtype genetics 2

HA codes for hemagglutinin, an antigenic glycoprotein found on the surface of the influenza viruses and is responsible for binding the virus to the cell that is being infected. NA codes for neuraminidase, an antigenic glycosylated enzyme found on the surface of the influenza viruses. It facilitates the release of progeny viruses from infected cells.[5]

Subtype genetics 3

Influenza viruses have a relatively high mutation rate that is characteristic of RNA viruses. The segmentation of its genome facilitates genetic recombination by segment reassortment in hosts infected with two different strains of influenza viruses at the same time.[6][7]


In terms of a definite diagnosis for H5N1, cell culture or direct fluorescent antibody assay may be used; PCR is also available for this diagnostic purpose.[8][9]


In January 2020, the U.S. Food and Drug Administration (FDA) approved an adjuvanted influenza A (H5N1) monovalent vaccine.[10][11]Wearing gloves and washing hands should be done if contact is made with wild birds, as well as sick or dead poultry.[12]


There is no highly effective treatment for H5N1 flu, but oseltamivir, can sometimes inhibit the influenza virus from spreading inside the user's body; this drug has become a focus for some governments and organizations.[13]


In terms of individuals that need hospitalization for H5N1 subtype infection, mortality is 60 percent, hence prognosis in hospitalized individuals is poor.[14]

Epidemiology 1

The earliest infections of humans by H5N1 coincided with an epizootic of H5N1 influenza in Hong Kong's poultry population in 1997. This panzootic outbreak was stopped by the killing of the entire domestic poultry population within the territory. However, the disease has continued to spread; outbreaks were reported in Asia again in 2003. On December 21, 2009 the WHO announced a total of 447 cases which resulted in the deaths of 263 individuals.[3][15]

Epidemiology 2

On April 2022, in the U.S. state of Colorado a male was the first to test positive in the country for this subtype H5N1, though authorities indicate the possibility of spread of the infection is low.[16]


  1. 1.0 1.1 International Committee on Taxonomy of Viruses (2002). "46.0.1. Influenzavirus A". Archived from the original on 2004-12-07. Retrieved 2006-04-17.
  2. Li KS, Guan Y, Wang J, Smith GJ, Xu KM, Duan L, Rahardjo AP, Puthavathana P, Buranathai C, Nguyen TD, Estoepangestie AT, Chaisingh A, Auewarakul P, Long HT, Hanh NT, Webby RJ, Poon LL, Chen H, Shortridge KF, Yuen KY, Webster RG, Peiris JS (2004). "Genesis of a highly pathogenic and potentially pandemic H5N1 influenza virus in eastern Asia". Nature. 430 (6996): 209–213. Bibcode:2004Natur.430..209L. doi:10.1038/nature02746. PMID 15241415. S2CID 4410379.
    This was reprinted in 2005: Li KS, Guan Y, Wang J, Smith GJ, Xu KM, Duan L, Rahardjo AP, Puthavathana P, Buranathai C, Nguyen TD, Estoepangestie AT, Chaisingh A, Auewarakul P, Long HT, Hanh NT, Webby RJ, Poon LL, Chen H, Shortridge KF, Yuen KY, Webster RG, Peiris JS (2005). "Today's Pandemic Threat: Genesis of a Highly Pathogenic and Potentially Pandemic H5N1 Influenza Virus in Eastern Asia". In Knobler SL, Mack A, Mahmoud A, Lemon SM (eds.). The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005). Washington DC: The National Academies Press. pp. 116–130. Archived from the original on 2006-09-14.
  3. 3.0 3.1 "NIOSH alert: protecting poultry workers from avian influenza (bird flu)". CDC. 7 July 2020. doi:10.26616/NIOSHPUB2008128. Retrieved 12 May 2022.
  4. Russell, Rupert J.; Haire, Lesley F.; Stevens, David J.; Collins, Patrick J.; Lin, Yi Pu; Blackburn, G. Michael; Hay, Alan J.; Gamblin, Steven J.; Skehel, John J. (7 September 2006). "The structure of H5N1 avian influenza neuraminidase suggests new opportunities for drug design". Nature. 443 (7107): 45–49. doi:10.1038/nature05114. ISSN 1476-4687. Archived from the original on 25 March 2022. Retrieved 11 May 2022.
  5. Couch, R. (1996). "Chapter 58. Orthomyxoviruses Multiplication". In Baron, S. (ed.). Medical Microbiology. Galveston: The University of Texas Medical Branch at Galveston. ISBN 978-0-9631172-1-2. Archived from the original on May 3, 2009.
  6. Kou, Z.; Lei, F. M.; Yu, J.; Fan, Z. J.; Yin, Z. H.; Jia, C. X.; Xiong, K. J.; Sun, Y. H.; Zhang, X. W.; Wu, X. M.; Gao, X. B.; Li, T. X. (15 December 2005). "New Genotype of Avian Influenza H5N1 Viruses Isolated from Tree Sparrows in China". Journal of Virology. 79 (24): 15460–15466. doi:10.1128/JVI.79.24.15460-15466.2005. Retrieved 15 May 2022.
  7. "Evolution of H5N1 Avian Influenza Viruses in Asia". Emerging Infectious Diseases. 11 (10): 1515–1526. October 2005. doi:10.3201/eid1110.050644. Retrieved 15 May 2022.
  8. Shinya, Kyoko; Hatta, Masato; Yamada, Shinya; Takada, Ayato; Watanabe, Shinji; Halfmann, Peter; Horimoto, Taisuke; Neumann, Gabriele; Kim, Jin Hyun; Lim, Wilina; Guan, Yi; Peiris, Malik; Kiso, Makoto; Suzuki, Takashi; Suzuki, Yasuo; Kawaoka, Yoshihiro (August 2005). "Characterization of a Human H5N1 Influenza A Virus Isolated in 2003". Journal of Virology. 79 (15): 9926–9932. doi:10.1128/JVI.79.15.9926-9932.2005. Archived from the original on 11 May 2022. Retrieved 11 May 2022.
  9. Habib-Bein, Nadia F.; Beckwith, William H.; Mayo, Donald; Landry, Marie L. (August 2003). "Comparison of SmartCycler Real-Time Reverse Transcription-PCR Assay in a Public Health Laboratory with Direct Immunofluorescence and Cell Culture Assays in a Medical Center for Detection of Influenza A Virus". Journal of Clinical Microbiology. 41 (8): 3597–3601. doi:10.1128/JCM.41.8.3597-3601.2003. Archived from the original on 24 April 2022. Retrieved 11 May 2022.
  10. Keown, Alex (4 February 2020). "FDA Approves Seqirus' Audenz as Vaccine Against Potential Flu Pandemic". BioSpace. Retrieved 5 February 2020.
  11. Research, Center for Biologics Evaluation and (29 November 2021). "AUDENZ". FDA. Retrieved 18 May 2022.
  12. "Prevention and Antiviral Treatment of Bird Flu Viruses in People | Avian Influenza (Flu)". 18 March 2022. Retrieved 17 May 2022.
  13. Medline Plus (2006-01-12). "Oseltamivir (Systemic)". National Institutes of Health (NIH). Archived from the original on 2006-04-25. Retrieved 2006-04-18.
  14. Sendor, Adam B.; Weerasuriya, Dilani; Sapra, Amit (2022). "Avian Influenza". StatPearls. StatPearls Publishing. Retrieved 18 May 2022.
  15. "Cumulative Number of Confirmed Human Cases for Avian Influenza A/(H5N1) Reported to WHO, 2003–2011" (PDF). World Health Organization (WHO). Archived (PDF) from the original on 2011-10-27.
  16. "Colorado man first to test positive for bird flu in the U.S., likelihood of spread low". The Colorado Sun. 28 April 2022. Retrieved 19 May 2022.