Influenza A virus subtype H3N2

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Influenza A virus subtype H3N2
Virus classification OOjs UI icon edit-ltr.svg
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Negarnaviricota
Class: Insthoviricetes
Order: Articulavirales
Family: Orthomyxoviridae
Genus: Alphainfluenzavirus
Species:
Influenza virus
Serotype:
Influenza A virus subtype H3N2
Notable strains

Influenza A virus subtype H3N2 (A/H3N2) is a subtype of influenza A virus (IAV). Some human-adapted strains of A/H3N2 are endemic in humans and are one cause of seasonal influenza (flu). [1] Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). [2] Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. [3]

Contents

All subtypes of IAV share a negative-sense, segmented RNA genome. [1] Under rare circumstances, one strain of the virus can acquire genetic material through genetic reassortment from a different strain and thus evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another. [4] [5] Major outbreaks of A/H3N2 strains in humans include Hong Kong Flu (1968–1969), and Fujian flu (2003–2004).

Each year, three influenza strains are chosen for inclusion in the forthcoming year's seasonal flu vaccination by the Global Influenza Surveillance and Response System of the World Health Organization (WHO). Since 1999, every annual formulation has included one strain of A/H3N2 as well as two other influenza strains - together representing strains thought most likely to cause significant human suffering in the coming season. [6] [7] [8]

Seasonal flu

Seasonal influenza is an annually recurring outbreak of flu, which occurs during the cold half of the year in each hemisphere. [9] Annually, about 3 to 5 million cases of severe illness and 290,000 to 650,000 deaths from seasonal flu occur worldwide. [10] A/H3N2 is one of the prevalent subtypes of flu which contribute to seasonal flu outbreaks, and a strain of A/H3N2 is usually included in the biannual reformulation of the flu vaccine. [11]

Swine flu

Pigs can harbor influenza viruses adapted to humans and others that are adapted to birds, allowing the viruses to exchange genes and create a pandemic strain. Sow with piglet.jpg
Pigs can harbor influenza viruses adapted to humans and others that are adapted to birds, allowing the viruses to exchange genes and create a pandemic strain.

A 2007 study reported: "In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world. In the United States, the classic H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. Most H3N2 virus isolates are triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages. Present vaccination strategies for swine influenza virus (SIV) control and prevention in swine farms typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses." [12]

Avian influenza virus H3N2 is endemic in pigs in China, and has been detected in pigs in Vietnam, contributing to the emergence of new variant strains. Pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome subunits by genetic reassortment) with H5N1, passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000 humans. The dominant strain of annual flu in humans in January 2006 was H3N2. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans had increased to 91% by 2005. In August 2004, researchers in China found H5N1 in pigs. [13]

Significant outbreaks

Hong Kong Flu (1968–1969)

The influenza viruses that caused Hong Kong flu (magnified about 100,000 times) Influenza virus.png
The influenza viruses that caused Hong Kong flu (magnified about 100,000 times)

The Hong Kong Flu was a flu pandemic caused by a strain of H3N2 descended from H2N2 by antigenic shift, in which genes from multiple subtypes reassorted to form a new virus. This pandemic of 1968 and 1969 killed an estimated one million people worldwide. [14] [15] [16] The pandemic infected an estimated 500,000 Hong Kong residents, 15% of the population, with a low death rate. [17] In the United States, about 100,000 people died. [18]

Both the H2N2 and H3N2 pandemic flu strains contained genes from avian influenza viruses. The new subtypes arose in pigs coinfected with avian and human viruses and were soon transferred to humans. Swine were considered the original "intermediate host" for influenza, because they supported reassortment of divergent subtypes. However, other hosts appear capable of similar coinfection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible. H1N1 may have been transmitted directly from birds to humans (Belshe 2005). [19]

The Hong Kong flu strain shared internal genes and the neuraminidase with the 1957 Asian flu (H2N2). Accumulated antibodies to the neuraminidase or internal proteins may have resulted in much fewer casualties than most pandemics. However, cross-immunity within and between subtypes of influenza is poorly understood.[ citation needed ]

The Hong Kong flu was the first known outbreak of the H3N2 strain, though there is serologic evidence of H3N2 infections in the late 19th century. The first record of the outbreak in Hong Kong appeared on 13 July 1968 in an area with a density of about 500 people per acre in an urban setting. The outbreak reached maximum intensity in two weeks, lasting six weeks in total. The virus was isolated in Queen Mary Hospital. Flu symptoms lasted four to five days. [17]

By July 1968, extensive outbreaks were reported in Vietnam and Singapore. By September 1968, it reached India, the Philippines, northern Australia and Europe. That same month, the virus entered California from United States troops returning from the Vietnam War. It reached Japan, Africa and South America in 1969. [17]

Fujian flu (2003–2004)

Diagram of influenza virus nomenclature InfluenzaNomenclatureDiagram.svg
Diagram of influenza virus nomenclature

Fujian flu refers to flu caused by either a Fujian human flu strain of the H3N2 subtype or a Fujian bird flu strain of the H5N1 subtype of the Influenza A virus. These strains are named after Fujian province in China.

A/Fujian (H3N2) human flu (from A/Fujian/411/2002(H3N2)-like flu virus strains) caused an unusually severe 2003–2004 flu season. This was due to a reassortment event that caused a minor clade to provide a haemagglutinin gene that later became part of the dominant strain in the 2002–2003 flu season. A/Fujian (H3N2) was made part of the trivalent influenza vaccine for the 2004–2005 flu season. [20]

See also

Related Research Articles

<i>Influenza A virus</i> Species of virus

Influenza A virus (IAV) is the only species of the genus Alphainfluenzavirus of the virus family Orthomyxoviridae. It is a pathogen with strains that infect birds and some mammals, as well as causing seasonal flu in humans. Mammals in which different strains of IAV circulate with sustained transmission are bats, pigs, horses and dogs; other mammals can occasionally become infected.

<span class="mw-page-title-main">Avian influenza</span> Influenza caused by viruses adapted to birds

Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A virus, which is enzootic in many bird populations.

<span class="mw-page-title-main">Antigenic shift</span> Process by which two or more different strains of a virus combine to form a new subtype

Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. The term is often applied specifically to influenza, as that is the best-known example, but the process is also known to occur with other viruses, such as visna virus in sheep. Antigenic shift is a specific case of reassortment or viral shift that confers a phenotypic change.

<i>Orthomyxoviridae</i> Family of RNA viruses including the influenza viruses

Orthomyxoviridae is a family of negative-sense RNA viruses. It includes seven genera: Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, Deltainfluenzavirus, Isavirus, Thogotovirus, and Quaranjavirus. The first four genera contain viruses that cause influenza in birds and mammals, including humans. Isaviruses infect salmon; the thogotoviruses are arboviruses, infecting vertebrates and invertebrates. The Quaranjaviruses are also arboviruses, infecting vertebrates (birds) and invertebrates (arthropods).

<span class="mw-page-title-main">Influenza A virus subtype H5N1</span> Subtype of influenza A virus

Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals that have been exposed to infected birds; in these cases, symptoms are frequently severe or fatal.

The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic that occurred in 1968 and 1969 and which killed between one and four million people globally. It is among the deadliest pandemics in history, and was caused by an H3N2 strain of the influenza A virus. The virus was descended from H2N2 through antigenic shift, a genetic process in which genes from multiple subtypes are reassorted to form a new virus.

<span class="mw-page-title-main">Swine influenza</span> Infection caused by influenza viruses endemic to pigs

Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.

<span class="mw-page-title-main">Influenza A virus subtype H1N1</span> Subtype of Influenza A virus

Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.

<span class="mw-page-title-main">Influenza pandemic</span> Pandemic involving influenza

An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been six major influenza epidemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.

<span class="mw-page-title-main">Influenza A virus subtype H2N2</span> Subtype of Influenza A virus

Influenza A virus subtype H2N2 (A/H2N2) is a subtype of Influenza A virus. H2N2 has mutated into various strains including the "Asian flu" strain, H3N2, and various strains found in birds. It is also suspected of causing a human pandemic in 1889. The geographic spreading of the 1889 Russian flu has been studied and published.

<span class="mw-page-title-main">Global spread of H5N1</span> Spread of bird flu

The global spread of H5N1 influenza in birds is considered a significant pandemic threat. While other H5N1 influenza strains are known, they are significantly different on a genetic level from a highly pathogenic, emergent strain of H5N1, which was able to achieve hitherto unprecedented global spread in 2008. The H5N1 strain is a fast-mutating, highly pathogenic avian influenza virus (HPAI) found in multiple bird species. It is both epizootic and panzootic. Unless otherwise indicated, "H5N1" in this timeline refers to the 2008 highly pathogenic strain of H5N1.

<i>Influenza B virus</i> Species of virus

Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae.

<span class="mw-page-title-main">Influenza A virus subtype H1N2</span> Virus subtype

Influenza A virus subtype H1N2 (A/H1N2) is a subtype of the species Influenza A virus. It is currently endemic in pig populations and is occasionally seen in humans.

<span class="mw-page-title-main">H5N1 genetic structure</span> Genetic structure of Influenza A virus

The genetic structure of H5N1, a highly pathogenic avian influenza virus, is characterized by a segmented RNA genome consisting of eight gene segments that encode for various viral proteins essential for replication, host adaptation, and immune evasion.

<span class="mw-page-title-main">Fujian flu</span> Strains of influenza

Fujian flu refers to flu caused by either a Fujian human flu strain of the H3N2 subtype of the Influenza A virus or a Fujian bird flu strain of the H5N1 subtype of the Influenza A virus. These strains are named after Fujian, a coastal province in Southeast China.

<span class="mw-page-title-main">Goose Guangdong virus</span> Strain of H5N1 influenza virus

The Goose Guangdong virus refers to the strain A/Goose/Guangdong/1/96 (Gs/Gd)-like H5N1 HPAI viruses. It is a strain of the Influenzavirus A subtype H5N1 virus that was first detected in a goose in Guangdong in 1996. It is an HPAI virus, meaning that it can kill a very high percentage of chickens in a flock in mere days. It is believed to be the immediate precursor of the current dominant strain of HPAI A(H5N1) that evolved from 1999 to 2002 creating the Z genotype that is spreading globally and is epizootic and panzootic, killing tens of millions of birds and spurring the culling of hundreds of millions of others to stem its spread.

<span class="mw-page-title-main">Influenza</span> Infectious disease

Influenza, commonly known as "the flu" or just "flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.

<span class="mw-page-title-main">2009 swine flu pandemic</span> 2009–2010 pandemic of swine influenza caused by H1N1 influenza virus

The 2009 swine flu pandemic, caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving the H1N1 virus. The first identified human case was in La Gloria, Mexico, a rural town in Veracruz. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "swine flu".

<span class="mw-page-title-main">Pandemic H1N1/09 virus</span> Virus responsible for the 2009 swine flu pandemic

The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.

Type A influenza vaccine is for the prevention of infection of influenza A virus and also the influenza-related complications. Different monovalent type A influenza vaccines have been developed for different subtypes of influenza A virus including H1N1 and H5N1. Both intramuscular injection or intranasal spray are available on market. Unlike the seasonal influenza vaccines which are used annually, they are usually used during the outbreak of certain strand of subtypes of influenza A. Common adverse effects includes injection site reaction and local tenderness. Incidences of headache and myalgia were also reported with H1N1 whereas cases of fever has also been demonstrated with H5N1 vaccines. It is stated that immunosuppressant therapies would reduce the therapeutic effects of vaccines and that people with egg allergy should go for the egg-free preparations.

References

  1. 1 2 "Influenza A Subtypes and the Species Affected | Seasonal Influenza (Flu) | CDC". Centers for Disease Control and Prevention. 2024-05-13. Retrieved 2024-06-17.
  2. ↑ Jilani TN, Jamil RT, Siddiqui AH (November 30, 2020). "H1N1 Influenza". H1N1 Influenza in StatPearls. StatPearls. PMID   30020613. Archived from the original on 12 March 2020. Retrieved 25 August 2020.
  3. ↑ CDC (2024-02-01). "Influenza Type A Viruses". Centers for Disease Control and Prevention. Retrieved 2024-05-03.
  4. ↑ Shao W, Li X, Goraya MU, Wang S, Chen JL (August 2017). "Evolution of Influenza A Virus by Mutation and Re-Assortment". International Journal of Molecular Sciences. 18 (8): 1650. doi: 10.3390/ijms18081650 . PMC   5578040 . PMID   28783091.
  5. ↑ Eisfeld AJ, Neumann G, Kawaoka Y (January 2015). "At the centre: influenza A virus ribonucleoproteins". Nature Reviews. Microbiology. 13 (1): 28–41. doi:10.1038/nrmicro3367. PMC   5619696 . PMID   25417656.
  6. ↑ "Seasonal Flu Vaccines | CDC". Centers for Disease Control and Prevention. 2024-03-12. Retrieved 2024-08-19.
  7. ↑ "Global Influenza Surveillance and Response System (GISRS)". World Health Organization. Archived from the original on October 3, 2011. Retrieved October 22, 2019.
  8. ↑ Anker M, Schaaf D, World Health Organization (2000). WHO report on global surveillance of epidemic-prone infectious diseases (PDF) (Report). World Health Organization (WHO). hdl: 10665/66485 . WHO/CDS/CSR/ISR/2000.1. Archived (PDF) from the original on 31 October 2022.
  9. ↑ "National Institute of Allergy and Infectious Diseases (NIAID) Factsheet". Archived from the original on 13 October 2005. Retrieved 8 October 2005.
  10. ↑ "Influenza (Seasonal)". World Health Organization (WHO). Retrieved 2021-05-10.
  11. ↑ Daum, L. T.; Shaw, M. W.; Klimov, A. I.; Canas, L. C.; Macias, E. A.; Niemeyer, D.; Chambers, J. P.; Renthal, R.; Shrestha, S. K.; Acharya, R. P.; Huzdar, S. P.; Rimal, N.; Myint, K. S.; Gould, P. (August 2005). "Influenza A (H3N2) outbreak, Nepal". Emerging Infectious Diseases . 11 (10): 1186–1191. doi:10.3201/eid1108.050302. PMC   3320503 . PMID   16102305.
  12. ↑ René Gramer, Marie; Hoon Lee, Jee; Ki Choi, Young; Goyal, Sagar M.; Soo Joo, Han (2007). "Serologic and genetic characterization of North American H3N2 swine influenza A viruses". Canadian Journal of Veterinary Research. 71 (3): 201–206. PMC   1899866 . PMID   17695595.
  13. ↑ WHO (28 October 2005). "H5N1 avian influenza: timeline" (PDF). Archived from the original (PDF) on 27 July 2011.
  14. ↑ Paul, William E. (2008). Fundamental Immunology. Lippincott Williams & Wilkins. p. 1273. ISBN   9780781765190.
  15. ↑ "World health group issues alert Mexican president tries to isolate those with swine flu". Associated Press. April 25, 2009. Retrieved 2009-04-26.
  16. ↑ Mandel, Michael (April 26, 2009). "No need to panic ... yet Ontario officials are worried swine flu could be pandemic, killing thousands". Toronto Sun. Archived from the original on 2009-06-01. Retrieved 2009-04-26.
  17. 1 2 3 Starling, Arthur (2006). Plague, SARS, and the Story of Medicine in Hong Kong. HK University Press. p. 55. ISBN   978-962-209-805-3.
  18. ↑ "1968 Pandemic (H3N2 Virus)". Centers for Disease Control and Prevention . U.S. Department of Health and Human Services. 22 January 2019. Retrieved 16 March 2020.
  19. ↑ Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner Archived 2017-08-09 at the Wayback Machine from excellent free on-line book Influenza Report 2006
  20. ↑ CDC article Update: Influenza Activity—United States and Worldwide, 2003–04 Season, and Composition of the 2004–05 Influenza Vaccine published 2 July 2004

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