Influenza A virus subtype H3N2

H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of proteins on the surface of its coat, hemagglutinin (H) and neuraminidase (N). H3N2 viruses can infect birds and mammals. In birds, humans and pigs the virus has mutated into many strains. H3N2 exchanges genes for internal proteins with other influenza subtypes.

The annual flu (also called "seasonal flu" or "human flu") kills an estimated 36,000 people in the United States each year. Flu vaccines are based on predicting which mutants of H1N1, H3N2, H1N2, and influenza B will proliferate in the next season. Separate vaccines are developed for the northern and southern hemispheres in preparation for their annual epidemics. In the tropics, influenza shows no clear seasonality. In the past ten years, H3N2 has tended to dominate in prevalence over H1N1, H1N2, and influenza B. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 has increased from 1% in 1994 to 12% in 2003 to 91% in 2005. [ [http://www.reason.com/rb/rb101905.shtml Reason] [http://www.nytimes.com/2006/01/15/health/15drugs.html New York Times] ]

easonal H3N2 flu

Seasonal H3N2 flu is a human flu from H3N2 that is slightly different from one of last year's flu season H3N2 variants. "Seasonal influenza viruses flow out of overlapping epidemics in East and Southeast Asia, then trickle around the globe before dying off. [Identifying] the source of the viruses allows global health officials to better predict which viruses are most likely to cause the most disease over the next year. [An analysis of] 13,000 samples of influenza A/H3N2 virus that were collected across six continents from 2002 to 2007 by the WHO's Global Influenza Surveillance Network [showed that] newly emerging strains of H3N2 appeared in East and Southeast Asian countries about 6 to 9 months earlier than anywhere else. The strains generally reached Australia and New Zealand next, followed by North America and Europe. The new variants typically reached South America after an additional 6 to 9 months, the group reported." [ [http://www.cidrap.umn.edu/cidrap/content/influenza/general/news/apr1608influenza.html CIDRAP] article "Study: New seasonal flu strains launch from Asia" published April 16, 2008 ]

wine flu

"In swine, 3 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 SIV control and prevention in swine farms typically include the use of 1 of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to 3 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 that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses." [ [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1899866 pubmedcentral.nih.gov] Canadian Journal of Veterinary Research (2007 July; 71(3): 201–206.) article "Serologic and genetic characterization of North American H3N2 swine influenza A viruses" by Marie René Gramer, Jee Hoon Lee, Young Ki Choi, Sagar M. Goyal, and Han Soo Joo]

Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units 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 is H3N2. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans has increased to 91% in 2005. A combination of these two subtypes of the species known as the avian influenza virus in a country like China is a worst case scenario. In August 2004, researchers in China found H5N1 in pigs.cite web
url=http://www.who.int/csr/disease/avian_influenza/Timeline_28_10a.pdf
title=H5N1 avian influenza: timeline
author=WHO
date=October 28, 2005]

Hong Kong Flu (1968-1969)

The Hong Kong Flu was a category 2 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. The Hong Kong Flu pandemic of 1968 and 1969 infected an estimated 500,000 people with a low death rate.Starling, Arthur. [2006] (2006) Plague, SARS, and the Story of Medicine in Hong Kong. HK University Press. ISBN 9622098053] [(Detailed chart of its evolution [http://www.eletrica.ufsj.edu.br/~nepomuceno/references/epidemiology/ear_eal02.pdf here] .)] Fifty million people were infected in the United States, resulting in an estimated 34,000 deaths. [Digitized Editorial Research Reports By Congressional Quarterly, inc 1986]

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). [ [http://www.influenzareport.com/ir/ai.htm Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner] from excellent free on-line Book called "Influenza Report 2006" which is a medical textbook that provides a comprehensive overview of epidemic and pandemic influenza."]

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.

The Hong Kong flu was the first known outbreak of the H3N2 strain, though there is serologic evidence of H3N? infections in the late 19th century. The first record of the outbreak in Hong Kong appeared on July 13, 1968 in an area with a density of about 500 people per acre in an urban setting. The outbreak reached maximum intensity in 2 weeks, lasting 6 weeks in total. The virus was isolated in Queen Mary Hospital. Flu symptoms lasted 4 to 5 days.

By July 1968, extensive outbreaks were reported in Vietnam and Singapore. By September 1968, it would reach India, Philippines, northern Australia and Europe. That same month, the virus entered US California from returning Vietnam War troops. It would reach Japan, Africa and South America by 1969.

"Three strains of Hong Kong influenza virus isolated from humans were compared with a strain isolated from a calf for their ability to cause disease in calves. One of the human strains. A/Aichi/2/68, was detected for five days in a calf, but all three failed to cause signs of disease. Strain A/cal/Duschanbe/55/71 could be detected for seven days and caused an influenza-like illness in calves." [ [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=853249&dopt=Abstract J Infect Dis. 1977 Apr;135(4):678-80.] article "Strains of Hong Kong influenza virus in calves"]

Fujian flu (2003–2004)

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 of the People's Republic of China that is across the Taiwan strait from Taiwan. [Fujian also borders the north of China's Guangdong province, where Hong Kong is. Hong Kong is important in the early history of H5N1.]

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 and its descendants are still the most common human H3N2 strain.

2004-2005 flu season

The 2004–05 trivalent influenza vaccine for the United States contained A/New Caledonia/20/99-like (H1N1), A/Fujian/411/2002-like (H3N2), and B/Shanghai/361/2002-like viruses. [http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5325a1.htm CDC] article "Update: Influenza Activity — United States and Worldwide, 2003–04 Season, and Composition of the 2004–05 Influenza Vaccine" published July 2, 2004 ]

2005-2006 flu season

The vaccines produced for the 2005–2006 season use:
* an A/New Caledonia/20/1999-like(H1N1);
* an A/California/7/2004-like(H3N2) (or the antigenically equivalent strain A/New York/55/2004);
* a B/Jiangsu/10/2003-like viruses.

2006-2007 flu season

The 2006–2007 influenza vaccine composition recommended by the World Health Organization on February 15, 2006 and the U.S. FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) on February 17, 2006 use:
* an A/New Caledonia/20/99 (H1N1)-like virus;
* an A/Wisconsin/67/2005 (H3N2)-like virus (A/Wisconsin/67/2005 and A/Hiroshima/52/2005 strains);
* a B/Malaysia/2506/2004-like virus from B/Malaysia/2506/2004 and B/Ohio/1/2005 strains which are of B/Victoria/2/87 lineage. [ [http://www.cdc.gov/flu/professionals/vaccination/composition0607.htm CDC] [http://www.phac-aspc.gc.ca/fluwatch/05-06/w08_06/index.html fluwatch] B/Victoria/2/87 lineage]

2007-2008 flu season

The composition of influenza virus vaccines for use in the 2007–2008 Northern Hemisphere influenza season recommended by the World Health Organization on February 14, 2007 [ [http://www.who.int/csr/disease/influenza/vaccinesnorth2008/en/index1.html 14 February 2007: WHO information meeting (Morning)] ] was:
* an A/Solomon Islands/3/2006 (H1N1)-like virus;
* an A/Wisconsin/67/2005 (H3N2)-like virus (A/Wisconsin/67/2005 (H3N2) and A/Hiroshima/52/2005 were used at the time);
* a B/Malaysia/2506/2004-like virus [ [http://www.who.int/csr/disease/influenza/recommendations2007north/en/index.html WHO website recommendation for 2007-2008 season] ] [ [http://www.who.int/csr/disease/influenza/recommendationfinal22sept.pdf WHO — Recommended composition of influenza virus vaccines for use in the 2007-2008 influenza season] (PDF)]

"A/H3N2 has become the predominant flu subtype in the United States, and the record over the past 25 years shows that seasons dominated by H3N2 tend to be worse than those dominated by type A/H1N1 or type B." Many H3N2 viruses making people ill in this 2007-2008 flu season differ from the strains in the vaccine and may not be well covered by the vaccine strains. "The CDC has analyzed 250 viruses this season to determine how well they match up with the vaccine, the report says. Of 65 H3N2 isolates, 53 (81%) were characterized as A/Brisbane/10/2007-like, a variant that has evolved [notably] from the H3N2 strain in the vaccine—A/Wisconsin/67/2005." [ [http://www.cidrap.umn.edu/cidrap/content/influenza/general/news/feb1508flu.html CIDRAP] article "Flu widespread in 44 states, CDC reports" published February 15, 2008]

ee also

*Bird flu
*Dog flu
*Horse flu
*Human flu
*Swine flu

Further reading

* [http://www.nature.com/nature/journal/v437/n7062/fig_tab/nature04239_F1.html Graphic] showing H3N2 mutations, amino acid by amino acid, among 207 isolates completely sequenced by the Influenza Genome Sequencing Project.
* [http://www.cdc.gov/ncidod/EID/vol11no08/05-0302.htm Influenza A (H3N2) Outbreak, Nepal]
* [http://www.bupa.co.uk/health_information/html/health_news/131103fujian.html Hot topic - Fujian-like strain A influenza]
* [http://www.idexx.com/production/swine/swine_influh3n2.jsp Monitoring Antibodies for Swine Influenza H3N2 Virus]
* [http://www.who.int/csr/don/2004_01_13a/en/ Human influenza A(H3N2) activity remains widespread in many countries - update 7]
* [http://www.who.int/csr/don/2004_01_21/en/ Human influenza A/H3N2 activity increases in many countries in central and eastern Europe - update 8]
* [http://www.medmall.org/Proflu/page5.html Influenza A H3N2]
* [http://www.newscientist.com/popuparticle.ns?id=in70 New Scientist: Bird Flu]

ources