The pandemic H1N1/09 virus is a
swine origin
influenza A virus subtype H1N1
In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the Spanish flu, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus ...
strain
Strain may refer to:
Science and technology
* Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes
* Strain (chemistry), a chemical stress of a molecule
* Strain (injury), an injury to a mu ...
that was responsible for the
2009 swine flu pandemic
The 2009 swine flu pandemic, caused by the H1N1 influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920 Span ...
. This strain is often called swine flu by the public media. For other names, see the
Nomenclature
Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal naming conventions, conventions of everyday speech to the i ...
section below.
Viral characteristics
The
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
is a novel strain of the
influenza virus
''Orthomyxoviridae'' (from Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' 'mucus') is a family of negative-sense RNA viruses. It includes seven genera: ''Alphainfluenzavirus'', ''Betainfluenzavirus'', '' Gammainfluenzavirus'', ...
,
for which existing
vaccines
A vaccine is a biological preparation that provides active acquired immunity
The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and pro ...
against
seasonal flu
Flu season is an annually recurring time period characterized by the prevalence of an outbreak of influenza (flu). The season occurs during the cold half of the year in each hemisphere. It takes approximately two days to show symptoms. Influen ...
provided no protection. A study at the
U.S.
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
(CDC) published in May 2009 found that children had no preexisting
immunity
Immunity may refer to:
Medicine
* Immunity (medical), resistance of an organism to infection or disease
* ''Immunity'' (journal), a scientific journal published by Cell Press
Biology
* Immune system
Engineering
* Radiofrequence immunity desc ...
to the new strain but that adults, particularly those over 60, had some degree of immunity. Children showed no
cross-reactive antibody
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
reaction to the then-new strain, while adults aged 18 to 64 had 6–9%, and older adults 34%.
[
] Much reporting of early analysis repeated that the strain contained genes from five different flu viruses: North American
swine influenza
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 o ...
, North American avian influenza, human influenza, and two swine influenza viruses typically found in Asia and Europe.
Further analysis showed that several of the
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s of the virus are most similar to strains that cause mild symptoms in humans, leading
virologist
Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their ...
Wendy Barclay to suggest that the virus was unlikely to cause severe symptoms for most people. Other leading researchers indicated that all segments of the virus were in fact swine in origin, despite it being a multiple reassortment. The first complete
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
sequence of the
pandemic
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...
strain was deposited in public databases on April 27, 2009, by scientists from the U.S. Centers for Disease Control and Prevention in Atlanta.
Scientists in Winnipeg later completed the full
genetic sequencing of viruses from Mexico and Canada on May 6, 2009.
Viral origins
Analysis of the genetic divergence of the virus in samples from different cases indicated that the virus jumped to humans in 2008, probably after June, and not later than the end of November,
likely around September 2008.
A report by researchers at the
Mount Sinai School of Medicine
The Icahn School of Medicine at Mount Sinai (ISMMS or Mount Sinai), formerly the Mount Sinai School of Medicine, is a private medical school in New York City. It is the academic teaching arm of the Mount Sinai Health System, which manages eigh ...
in 2016 found that the 2009 H1N1 virus likely originated from pigs in a very small region of central Mexico.
On April 17, 2009, the
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
(CDC) determined that two cases of febrile respiratory illness occurring in children who resided in adjacent counties in
Southern California
Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most po ...
were caused by infection with a swine influenza A (H1N1) virus. The viruses from the two cases were closely related genetically, resistant to amantadine and rimantadine, and contain a unique combination of gene segments that previously had not been reported among swine or human influenza viruses in the United States or elsewhere. After the emergence of the novel virus in the spring of 2009, it spread quickly across the United States, Mexico and the world.
In late April, the
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) declared its first ever "public health emergency of international concern", or
PHEIC
A public health emergency of international concern (PHEIC) is a formal declaration by the World Health Organization (WHO) of "an extraordinary event which is determined to constitute a public health risk to other States through the internatio ...
, and in June, the WHO and the U.S. CDC stopped counting cases and declared the outbreak a
pandemic
A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic (epidemiology), endemic disease wi ...
.
On June 23, 2009, ''The New York Times'' reported that U.S. federal agriculture officials believed that, "contrary to the popular assumption that the new swine flu pandemic arose on
factory farms
Intensive animal farming or industrial livestock production, also known by its opponents as factory farming and macro-farms, is a type of intensive agriculture, specifically an approach to animal husbandry designed to maximize production, while ...
in Mexico", now believe it "most likely emerged in pigs in Asia, but then traveled to North America in a human". They emphasized that there was no way to prove their hypothesis but said there is no evidence this new virus, which combines Eurasian and North American genes, has never circulated in North American pigs, "while there is tantalizing evidence that a closely related 'sister virus' has circulated in Asia".
However, a subsequent report by researchers at the Mount Sinai School of Medicine in 2016 found that the 2009 H1N1 virus likely originated in central Mexico.
In early June 2009, using computational methods developed over the previous ten years, an international team of researchers attempted to reconstruct the origins and timescale of the 2009 flu pandemic.
Oliver Pybus
Oliver George Pybus is a British biologist. He is professor of evolution and infectious disease at the University of Oxford and professor of infectious diseases at the Royal Veterinary College. He is also editor-in-chief of Virus Evolution
and co ...
of Oxford University's Department of Zoology, and part of the research team, claims "Our results show that this strain has been circulating among pigs, possibly among multiple continents, for many years prior to its transmission to humans." The research team who worked on this case also believed it was "derived from several viruses circulating in swine", and that the initial transmission to humans occurred several months before recognition of the outbreak. The team concluded that "despite widespread influenza surveillance in humans, the lack of systematic swine surveillance allowed for the undetected persistence and evolution of this potentially pandemic strain for many years."
[
* ]
![3D Influenza virus](https://upload.wikimedia.org/wikipedia/commons/3/3b/3D_Influenza_virus.png)
According to the researchers, movement of live pigs between Eurasia and North America "seems to have facilitated the mixing of diverse swine influenza viruses, leading to the multiple reassortment events associated with the genesis of the (new H1N1) strain". They also said this new pandemic "provides further evidence of the role of domestic pigs in the ecosystem of influenza A".
["New flu has been around for years in pigs—study"]
''Reuters'', June 11, 2009
In November 2009, a study was published in ''
Virology Journal
''Virology Journal'' is an open-access peer-reviewed medical journal published by BioMed Central. It publishes research related to viruses and the prevention of viral infection (including vaccination, the use of antiviral agents, and gene therap ...
'' in which it was suggested that the virus may be the product of three strains from three continents that swapped genes in a lab or a vaccine-making plant, and subsequently "escaped". The study followed debate among researchers in May 2009, when the authors asked the
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) to consider the hypothesis. After reviewing the initial paper, WHO and other organizations concluded the pandemic strain was a naturally-occurring virus and not laboratory-derived.
Contagiousness
The virus is
contagious
Contagious may refer to:
* Contagious disease
Literature
* Contagious (magazine), a marketing publication
* ''Contagious'' (novel), a science fiction thriller novel by Scott Sigler
Music
Albums
*''Contagious'' (Peggy Scott-Adams album), 1997
* ...
with an
R0 of 1.4 to 1.6 and spreads from human to human in much the same way as seasonal flu. The most common mechanisms by which it spreads are by droplets from coughs and sneezes of infected people, and also potentially touching a surface or the hand of a person contaminated with the virus and then touching one's eyes, nose or mouth. In 2009, the WHO reported that H1N1/09 seemed to be more contagious than seasonal flu. However, a ''New England Journal of Medicine'' report said the transmissibility of the 2009 H1N1 influenza virus in households was lower than that seen in past pandemics. The U.S. CDC recommended that people should wait at least a day after their fever subsides (usually 3–4 days after the onset of symptoms) before resuming normal activities, but it has been found that they can continue to shed virus for several more days.
Virulence
The virulence of swine flu virus is mild and the mortality rates are very low.
In mid-2009, the U.S. CDC noted that most infections were mild, similar to seasonal flu, and that recovery tended to be fairly quick.
The number of deaths was said to be a tiny fraction of the annual number of deaths from seasonal flu. However, comparisons of human fatality figures with seasonal influenza are prone to underestimate impact of the pandemic, and the pandemic H1N1/09 virus was in fact the dominant strain of influenza causing illness in the 2009/10 flu season.
Research carried out at
Imperial College London
Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...
has shown that, unlike seasonal flu, H1N1/09 can infect cells deep in the lungs. Seasonal flu can infect only cells with receptor type a2-6 which are typically located in the nose and throat but H1N1/09 can also infect cells with receptor type a2-3. This may explain why some patients experience severe respiratory symptoms. (The
H5N1
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other animal species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of typ ...
virus is also able to infect cells deep in the lungs with receptor type a2-3 but cannot infect cells with receptor type a2-6 making it less contagious than H1N1/09.)
, most people infected by this flu suffered a mild illness, but the small minority hospitalized were often severely ill. Arand Kumar, an intensive care expert at the University of Manitoba, Winnipeg, Canada, said "this pandemic is like two diseases; either you're off work for a few days or you go to hospital, often to the intensive-care unit (ICU). There's no middle ground." In the southern hemisphere 15 to 33% of hospitalized cases went to the ICU in July and August 2009. Unlike H5N1 avian flu and
SARS
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sever ...
which provoke a runaway body-wide
immune response
An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...
, H1N1/09 destroys the
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s'
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit.
Uses in anatomy and zoology
* Pulmonary alveolus, an air sac in the lungs
** Alveolar cell or pneumocyte
** Alveolar duct
** Alveolar macrophage
* ...
, often causing
acute respiratory distress syndrome
Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Symptoms include shortness of breath (dyspnea), rapid breathing (tachypnea), and bluish skin colo ...
, which kills in half of all cases. Preliminary research suggests that severity is linked to a genetic variation in immune systems.
From April 2009 to November 2009, 3,900 people died of the H1N1 pandemic virus in the U.S. This is sometimes compared to the 36,000 people per year who die from the "common flu", mostly in winter, although this number is an estimate. The death rate of H1N1 in the U.S. was calculated as less than 0.02% from November 2009 figures from the CDC, and has been explicitly calculated as 0.026% in England.
Vaccine
![2009 H1N1 Swine Flu Line](https://upload.wikimedia.org/wikipedia/commons/4/43/2009_H1N1_Swine_Flu_Line.jpg)
A study at the U.S. Centers for Disease Control and Prevention published in May 2009 found that children had no preexisting immunity to the new strain but that adults, particularly those older than 60, had some degree of immunity. Children showed no cross-reactive antibody reaction to the new strain, adults aged 18 to 60 had 6–9%, and older adults 33%. While it has been thought that these findings suggest the partial immunity in older adults may be due to previous exposure to similar seasonal influenza viruses, a November 2009 study of a rural unvaccinated population in China found only a 0.3% cross-reactive antibody reaction to the H1N1 strain, suggesting that previous vaccinations for seasonal flu and not exposure may have resulted in the immunity found in the older U.S. population. Production may be three billion doses per year rather than the earlier estimate of five billion.
Evolutionary potential
On May 22, 2009, World Health Organization (WHO) Director-General
Margaret Chan
Margaret Chan Fung Fu-chun, (born 21 August 1947) is a Chinese-Canadian physician, who served as the Director-General of the World Health Organization (WHO) delegating the People's Republic of China from 2006–2017. Chan previously served a ...
said the virus must be closely monitored in the southern hemisphere, as it could mix with ordinary seasonal influenza and change in unpredictable ways. Experts writing in the July issue of ''The New England Journal of Medicine'' noted that historically, pandemic viruses have evolved between seasons, and the current strain may become more severe or transmissible in the coming months. They therefore stressed the importance of international cooperation to engage in proper surveillance to help monitor changes in the virus's behavior, which will aid in both "vaccine targeting" and interpreting illness patterns in the fall of 2009.
[
]
Other experts in 2009 were also concerned that the new virus strain could
mutate
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitos ...
over the coming months. Guan Yi, a leading virologist from the University of Hong Kong, for instance, described the new H1N1 influenza virus as "very unstable", meaning it could mix and swap genetic material (reassortment) when exposed to other viruses. During an interview he said, "Both H1N1 and H5N1 are unstable so the chances of them exchanging genetic material are higher, whereas a stable (seasonal flu) virus is less likely to take on genetic material." The H5N1 virus is mostly limited to birds, but in rare cases when it infects humans it has a mortality rate of between 60% to 70%.
Experts worry about the emergence of a hybrid of the more
virulent
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
Asian-lineage HPAI (highly pathogenic avian influenza) A/H5N1 strain (media labeled "bird flu") with more human-transmissible influenza A strains such as this novel 2009 swine-origin A/H1N1 strain (media labeled "swine flu"), especially since the H5N1 strain is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
among birds in countries like China, Indonesia, Vietnam and Egypt.
[ (See the suite of H5N1 articles for details.)
Other studies concluded that the virus was likely well adapted to humans, had a clear biological advantage over seasonal flu strains and that reassortment was unlikely at that time due to its ease in replication and transmission.][
] However, Federal health officials in the U.S. noted that the horrific 1918 flu epidemic
The 1918–1920 influenza pandemic, commonly known by the misnomer Spanish flu or as the Great Influenza epidemic, was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was ...
, which killed hundreds of thousands in the United States alone, was preceded by a mild "herald" wave of cases in the spring, followed by devastating waves of illness in the autumn. As of late July 2009, U.S. health officials said the swine flu wasn't yet mutating to become more dangerous, but they were closely tracking that as the virus continued to circle the globe.["CDC says no sign yet that swine flu is mutating"](_blank)
Associated Press, July 23, 2009
As of October 2009, research done by Taubenberger showed that the evolution of A (H1N1) is relatively slow since the structure of the 2009 H1N1 virus is similar to the strain of H1N1 implicated in the 1918 flu pandemic. A study from Hokkaido University found a sequence homology
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spe ...
between the Hemagglutinin
In molecular biology, hemagglutinins (or ''haemagglutinin'' in British English) (from the Greek , 'blood' + Latin , 'glue') are receptor-binding membrane fusion glycoproteins produced by viruses in the ''Paramyxoviridae'' family. Hemagglutinins ar ...
antigen
In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...
amino acid residues found in the earlier 1918 strain and the 2009 H1N1 strain. This may have played a role in individuals who had been infected with the 1918 strain and its early descendants in showing stronger specific immunity to the 2009 H1N1 virus. This finding provided insight into future monitoring of the H1N1 virus and its evolution within the human population.
Mutation
On November 20, 2013, the Norwegian Institute of Public Health released a statement saying they had discovered a potentially significant mutation in the H1N1 influenza strain that could be responsible for causing the severest symptoms among those infected. In the statement they said "The mutation could be affecting the virus' ability to go deeper into the respiratory system, thus causing more serious illness".[ABC News
http://www.abcnews.go.com/Health/wireStory?id=9138409 ]
The World Health Organization said the mutation did not appear to be widespread in Norway and the virus in its mutated form remained sensitive to antivirals
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...
and pandemic vaccines. A similar mutation had been detected in H1N1 viruses circulating in several other countries, including China and the United States, in severe as well as in some mild cases. "Although further investigation is under way, no evidence currently suggests that these mutations are leading to an unusual increase in the number of H1N1 infections or a greater number of severe or fatal cases."
On December 2, 2009, the WHO announced that they had been informed of two recent clusters of patients infected with oseltamivir-resistant H1N1 viruses. Both clusters, detected in the UK (including Wales) and in North Carolina, occurred in a single ward and involved patients whose immune systems were severely compromised or suppressed. Transmission of resistant virus from one patient to another is suspected in both outbreaks.
Resistance
, the WHO reported 314 samples of 2009 pandemic H1N1 flu tested worldwide have shown resistance to oseltamivir
Oseltamivir, sold under the brand name Tamiflu, is an antiviral medication used to treat and prevent influenza A and influenza B, viruses that cause the flu. Many medical organizations recommend it in people who have complications or are at hig ...
(Tamiflu).[
] This was not totally unexpected as 99.6% of the seasonal H1N1 flu strains tested have developed resistance to amantadine and rimantadine. no circulating flu had yet shown any resistance to zanamivir
Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and ap ...
(Relenza), the other available anti-viral.[
]
Species affected
;Swine
Before being transmitted to humans, a H1N1 type virus is known to have circulated in swine. In August 2007, about 25 people and 160 pigs developed flu at a county fair in Ohio. Analysis showed they were infected with the same strain—a H1N1 type containing genes of human, bird and swine origin. A 2004 study found that in Iowa, 20 percent of swine veterinarians and 3percent of meatpackers, but no university workers, had antibodies in their blood indicating they had been infected with swine flu. Another study, of 804 rural Iowans, found that pig farmers were 50 times more likely, and their spouses about 30 times more likely, than university workers to carry swine flu antibodies. Pigs are also known to have been infected by humans.
;Humans
Humans have been affected since early 2009. The November 27, 2009 worldwide update by the U.N.'s World Health Organization (WHO) states that "more than 207 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 7,820 deaths". The WHO has also tracked more than 622,482 laboratory-confirmed cases of H1N1. The symptoms of this virus are identical to that of seasonal influenza.
;Birds
In late August 2009, the government of Chile discovered that the human H1N1/09 virus had jumped, unmutated, to birds, "opening a new chapter in the global epidemic". Top flu and animal-health experts with the WHO and the CDC were monitoring the situation closely. They said the infected turkeys had suffered only mild effects, easing concern about a potentially dangerous development. Chile's turkey meat remained safe to eat, they said, and so far there had been no signs of a potentially dangerous mutation. Virus experts were concerned that a more dangerous and easily transmitted strain could emerge if H1N1/09 combines again with avian flu, which is far more virulent but much less contagious to humans. By October 2009, another outbreak was identified at a turkey breeder in Ontario, Canada.
;Other animals
In October 2009, a ferret
The ferret (''Mustela furo'') is a small, Domestication, domesticated species belonging to the family Mustelidae. The ferret is most likely a domesticated form of the wild European polecat (''Mustela putorius''), evidenced by their Hybrid (biol ...
exhibiting flu symptoms was confirmed to have contracted the H1N1 virus from its owner in Oregon. In November 2009, a case of novel H1N1 was confirmed in a household cat. Although the earliest cat fatality from the H1N1 virus in the U.S. occurred in Pennsylvania, the Oregon Veterinary Medical Association was the first to confirm a cat fatality in the U.S. The association recommended that cat owners with flu symptoms avoid touching cat's eyes, nose, and mouth while sick. They recommended thoroughly washing hands after handling a sick pet as it might be possible for cats to transmit the virus to humans. This was the third confirmed case of H1N1 in a cat in the U.S.; other cases have occurred in Utah and Iowa. The first case of a dog with H1N1 was reported in December 2009. On July 22, 2011 the Norwegian Veterinary Institute reported the first occurrence of 2009-H1N1 influenza virus in minks.
Nomenclature
The initial outbreak of a novel swine-origin H1N1
In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the Spanish flu, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus ...
flu pandemic
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region (either multiple continents or worldwide) and infects a large proportion of the population. There have been six major influenza epidemics in the last ...
in 2009 and the virus strain that caused it were called by many names. In July 2009, WHO experts named the virus "pandemic H1N1/09 virus" to distinguish it from both various seasonal H1N1 virus strains and the 1918 flu pandemic H1N1 strain.
Some authorities objected to calling the flu outbreak "swine flu". U.S. Agriculture Secretary Tom Vilsack
Thomas James Vilsack (; born December 13, 1950) is an American politician serving as the 32nd United States Secretary of Agriculture in the Biden administration. He previously served in the role from 2009 to 2017 during the Obama administration. ...
expressed concerns that this would lead to the misconception that pork
Pork is the culinary name for the meat of the domestic pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BCE.
Pork is eaten both freshly cooked and preserved; ...
is unsafe for consumption. The CDC began referring to it as "novel influenza A (H1N1)"; "A/H1N1" is sometimes used. The CDC stopped using the nomenclature "novel H1N1" and updated various web pages to reflect the change to "2009 H1N1 Flu". In the Netherlands it was originally called "pig flu" but, later called "Mexican flu" by the National Health Institute and in the media. South Korea and Israel briefly considered calling it the "Mexican virus". Later the South Korean press used "SI", short for "swine influenza". Taiwan suggested the names "H1N1 flu" or "new flu", which most local media adopted. The World Organization for Animal Health
The World Organisation for Animal Health (WOAH), formerly the (OIE), is an intergovernmental organization coordinating, supporting and promoting animal disease control.
Mission and status
The main objective of the WOAH is to control epizoo ...
proposed the name "North American influenza". The European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
adopted the term "novel flu virus".
The name A(H1N1)pdm09 later came into widespread use, sometimes qualified as A/California/7/2009(H1N1)pdm, etc.
The pdm09 in the above nomenclature refers to Pandemic Disease Mexico 2009.
Genetics
On April 24, 2009, the U.S. CDC determined that seven samples from suspected cases in Mexico matched the strain that had infected patients in Texas and California with no known linkages to animals or one another; the strain appeared to be spreading from human to human. The CDC determined that the strain contained genes from four different flu viruses—North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe—"an unusually mongrelised mix of genetic sequences".[
] A CDC investigative team arrived in Mexico City on April 25, 2009 to work with Mexican counterparts to study the virus.
Pigs are susceptible to influenza viruses that can also infect both humans and birds, so they may act as a "mixing vessel" in which reassortment can occur between flu viruses of several species. Reassortment
Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and chromosomal crossover. It is particula ...
is a process that happens if two different types of influenza virus infect a single cell and it can produce a new strain of influenza. This is because the virus genome is split between eight independent pieces of RNA, which allows pieces of RNA from different viruses to mix and form a novel type of virus as new virus particles are being assembled. This new strain appears to be a result of the reassortment of two swine influenza viruses, one from North America and one from Europe. But the North American pig strain was itself the product of previous reassortments, and has carried an avian PB2 gene for at least ten years and a human PB1 gene since 1993. These genes were passed on to the new virus.
Gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
sequences for every viral gene were made available through the Global Initiative on Sharing Avian Influenza Data (GISAID
GISAID (Global Initiative on Sharing Avian Influenza Data) is a global science initiative and primary source established in 2008 that provides open access to genomic data of influenza viruses and the coronavirus responsible for the COVID-19 pand ...
). A preliminary analysis found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase
Exo-α-sialidase (EC 3.2.1.18, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids:
: Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glycos ...
(NA) and matrix protein
Viral matrix proteins are structural proteins linking the viral envelope with the virus core. They play a crucial role in virus assembly, and interact with the RNP complex as well as with the viral membrane. They are found in many enveloped viruses ...
(M) genes resembled versions present in European swine flu isolates. While viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S. So far, little is known about the spread of the virus in any pig population. A preliminary analysis has also shown that several of the proteins involved in the pathophysiology
Pathophysiology ( physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is the ...
of the virus are most similar to strains that cause mild symptoms in humans. This suggests the virus is unlikely to cause severe infections similar to those caused by the 1918 pandemic flu virus or the H5N1 avian influenza.
Late on May 6, 2009, Canada's National Microbiology Laboratory
The National Microbiology Laboratory (NML) is part of the Public Health Agency of Canada (PHAC), the agency of the Government of Canada that is responsible for public health, health emergency preparedness and response, and infectious and chronic d ...
first completed the sequencing of Mexican samples of the virus, publishing the result to GenBank
The GenBank sequence database is an open access, annotated collection of all publicly available nucleotide sequences and their protein translations. It is produced and maintained by the National Center for Biotechnology Information (NCBI; a part ...
as A/Mexico/InDRE4487/2009(H1N1). This was later shown to be nearly identical to A/California/07/2009 (H1N1), the strain from California sequenced and published by the CDC on 27 April. Samples from Mexico, Nova Scotia and Ontario had the same sequence, ruling out genetic explanations for the greater severity of the Mexican cases.
The genetic divergence of the virus in samples from different cases has been analysed by an international collaboration who found that the virus jumped to humans in 2008, probably after June, and not later than the end of November.
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/ref> The research also indicated the virus had been latent in pigs for several months prior to the outbreak, suggesting a need to increase agricultural surveillance to prevent future outbreaks.[
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See also
* 2009 flu pandemic
The 2009 swine flu pandemic, caused by the H1N1 influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920 Span ...
* 2009 flu pandemic in Mexico
In March and April 2009, an outbreak of a new strain of influenza commonly referred to as "swine flu" infected many people in Mexico and other parts of the world, causing illness ranging from mild to severe. Initial reports suggested that ...
* COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...
* Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
* Swine influenza
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 o ...
References
External links
Gene sequence information
from Influenza Research Database
Graphical Image of the viral makeup of the 2009 pandemic h1n1 virus
– NEJM
EU response to influenza
EU coordination on Pandemic (H1N1) 2009
Microscopic image of the H1N1 virus
Microscopic image of the H1N1 virus
{{DEFAULTSORT:Pandemic H1n1 09 Virus
2009 swine flu pandemic
Influenza A virus subtype H1N1
Infraspecific virus taxa