INFLUENZA A (H1 N1 ) VIRUS is the subtype of influenza A virus that
was the most common cause of human influenza (flu) in 2009, and is
associated with the 1918 outbreak known as the
Spanish Flu .
It is an orthomyxovirus that contains the glycoproteins
haemagglutinin and neuraminidase . For this reason, they are described
H1N2 etc. depending on the type of H or N antigens they
express with metabolic synergy.
Haemagglutinin causes red blood cells
to clump together and binds the virus to the infected cell.
Neuraminidase are a type of glycoside hydrolase enzyme which help to
move the virus particles through the infected cell and assist in
budding from the host cells.
Some strains of H1N1 are endemic in humans and cause a small fraction
of all influenza-like illness and a small fraction of all seasonal
influenza . H1N1 strains caused a small percentage of all human flu
infections in 2004–2005. Other strains of H1N1 are endemic in pigs
(swine influenza ) and in birds (avian influenza ).
In June 2009, the
World Health Organization
World Health Organization (WHO) declared the new
strain of swine-origin H1N1 as a pandemic . This strain is often
called SWINE FLU by the public media. This novel virus spread
worldwide and had caused about 17,000 deaths by the start of 2010. On
August 10, 2010, the
World Health Organization
World Health Organization declared the H1N1
influenza pandemic over, saying worldwide flu activity had returned to
typical seasonal patterns.
* 2 Notable incidents
* 2.1 Spanish flu
* 2.2 Fort Dix outbreak
* 2.3 Russian flu
* 2.4 2009 A(H1N1) pandemic
* 2.5 2015 India outbreak
* 2.6 2017 Maldives outbreak
* 2.7 2017
* 3 In pregnancy
* 4 Additional images
* 5 Notes
* 6 External links
* 6.1 Nontechnical
* 6.2 Technical
Swine influenza (swine flu or pig flu) is a respiratory disease that
occurs in pigs that is caused by the
Influenza A virus. Influenza
viruses that are normally found in swine are known as swine influenza
viruses (SIVs). The known SIV strains include influenza C and the
subtypes of influenza A known as H1N1,
Pigs can also become infected with the H4N6 and H9N2 subtypes.
Swine influenza virus is common throughout pig populations worldwide.
Transmission of the virus from pigs to humans is not common and does
not always lead to human influenza, often resulting only in the
production of antibodies in the blood. If transmission does cause
human influenza, it is called zoonotic swine flu or a variant virus.
People with regular exposure to pigs are at increased risk of swine
flu infection. The meat of an infected animal poses no risk of
infection when properly cooked.
Pigs experimentally infected with the strain of swine flu that caused
the human pandemic of 2009–10 showed clinical signs of flu within
four days, and the virus spread to other uninfected pigs housed with
the infected ones.
During the mid-20th century, identification of influenza subtypes
became possible, allowing accurate diagnosis of transmission to
humans. Since then, only 50 such transmissions have been confirmed.
These strains of swine flu rarely pass from human to human. Symptoms
of zoonotic swine flu in humans are similar to those of influenza and
of influenza-like illness in general, namely chills, fever , sore
throat , muscle pains, severe headache , coughing, weakness, and
general discomfort. The recommended time of isolation is about five
1918 flu pandemic
1918 flu pandemic
The Spanish flu , also known as la grippe, La Gripe Española, or La
Pesadilla, was an unusually severe and deadly strain of swine
influenza , a viral infectious disease , that killed some 50 to 100
million people worldwide over about a year in 1918 and 1919. It is
thought to be one of the deadliest pandemics in human history .
The 1918 flu caused an unusual number of deaths, possibly due to it
causing a cytokine storm in the body. (The current
H5N1 bird flu ,
Influenza A virus, has a similar effect.) The Spanish flu
virus infected lung cells, leading to overstimulation of the immune
system via release of cytokines into the lung tissue. This leads to
extensive leukocyte migration towards the lungs, causing destruction
of lung tissue and secretion of liquid into the organ. This makes it
difficult for the patient to breathe. In contrast to other pandemics,
which mostly kill the old and the very young, the 1918 pandemic killed
unusual numbers of young adults, which may have been due to their
healthy immune systems mounting a too-strong and damaging response to
The term "Spanish" flu was coined because
Spain was at the time the
only European country where the press were printing reports of the
outbreak, which had killed thousands in the armies fighting World War
I . Other countries suppressed the news in order to protect morale.
FORT DIX OUTBREAK
1976 swine flu outbreak
In 1976, a novel swine influenza A (H1N1) caused severe respiratory
illness in 13 soldiers with 1 death at Fort Dix, New Jersey. The virus
was detected only from January 19 to February 9 and did not spread
beyond Fort Dix. Retrospective serologic testing subsequently
demonstrated that up to 230 soldiers had been infected with the novel
virus, which was an H1N1 strain. The cause of the outbreak is still
unknown and no exposure to pigs was identified.
The 1977–1978 Russian flu epidemic was caused by strain Influenza
A/USSR/90/77 (H1N1). It infected mostly children and young adults
under 23 because a similar strain was prevalent in 1947–57, causing
most adults to have substantial immunity. Because of a striking
similarity in the viral RNA of both strains – one which is unlikely
to appear in nature due to antigenic drift – it was speculated that
the later outbreak was due to a laboratory incident in Russia or
Northern China, though this was denied by scientists in those
countries. The virus was included in the 1978–1979 influenza
vaccine . See also
1889–1890 flu pandemic for the earlier
Russian flu pandemic caused either by
2009 A(H1N1) PANDEMIC
Illustration of influenza antigenic shift Main article: 2009
2009 flu pandemic
2009 flu pandemic , the virus isolated from patients in the
United States was found to be made up of genetic elements 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." This new strain appears to be a result of
reassortment of human influenza and swine influenza viruses, in all
four different strains of subtype H1N1.
Preliminary genetic characterization found that the hemagglutinin
(HA) gene was similar to that of swine flu viruses present in U.S.
pigs since 1999, but the neuraminidase (NA) and matrix protein (M)
genes resembled versions present in European swine flu isolates. The
six genes from American swine flu are themselves mixtures of swine
flu, bird flu, and human flu viruses. 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.
In April 2009, an outbreak of influenza-like illness (ILI) occurred
in Mexico and then in the United States; the CDC reported seven cases
of novel A/H1N1 influenza and promptly shared the genetic sequences on
the GISAID database. With similar timely sharing of data for Mexican
isolates, by April 24 it became clear that the outbreak of ILI in
Mexico and the confirmed cases of novel influenza A in the southwest
US were related and
WHO issued a health advisory on the outbreak of
"influenza-like illness in the United States and Mexico". The disease
then spread very rapidly, with the number of confirmed cases rising to
2,099 by May 7, despite aggressive measures taken by the Mexican
government to curb the spread of the disease. The outbreak had been
predicted a year earlier by noticing the increasing number of
replikins , a type of peptide , found in the virus.
On June 11, 2009, the
WHO declared an H1N1 pandemic, moving the alert
level to phase 6, marking the first global pandemic since the 1968
Hong Kong flu . On October 25, 2009, U.S. President Barack Obama
officially declared H1N1 a national emergency Despite President
Obama's concern, a
Fairleigh Dickinson University PublicMind poll
found in October 2009 that an overwhelming majority of New Jerseyans
(74%) were not very worried or not at all worried about contracting
the H1N1 flu virus. However, the President’s declaration caused
many U.S. employers to take actions to help stem the spread of the
swine flu and to accommodate employees and / or workflow which may be
impacted by an outbreak.
A study conducted in coordination with the University of Michigan
Health Service — scheduled for publication in the December 2009
American Journal of Roentgenology — warned that H1N1 flu can cause
pulmonary embolism , surmised as a leading cause of death in this
pandemic. The study authors suggest physician evaluation via contrast
enhanced CT scans for the presence of pulmonary emboli when caring for
patients diagnosed with respiratory complications from a "severe" case
of the H1N1 flu. However pulmonary embolism is not the only embolic
manifestation of H1N1 infection. H1N1 may induce a number of embolic
events such as myocardial infarction, bilateral massive DVT, arterial
thrombus of infrarenal aorta, thrombosis of right external Iliac vein
and common femoral vein or cerebral gas embolism. The type of embolic
events caused by H1N1 infection are summarized in a recently published
review by Dimitroulis Ioannis et al.
The March 21, 2010 worldwide update, by the U.N.'s World Health
Organization (WHO), states that "213 countries and overseas
territories/communities have reported laboratory confirmed cases of
pandemic influenza H1N1 2009, including at least 16,931 deaths." As
of May 30, 2010, worldwide update by World Health Organization(WHO)
more than 214 countries and overseas territories or communities have
reported laboratory confirmed cases of pandemic influenza H1N1 2009,
including over 18,138 deaths. The research team of Andrew Miller MD
showed pregnant patients are at increased risk. It has been suggested
that pregnant women and certain populations such as native North
Americans have a greater likelihood of developing a
T helper type 2
response to H1N1 influenza which may be responsible for the systemic
inflammatory response syndrome that causes pulmonary edema and death.
On 26 April 2011, an H1N1 pandemic preparedness alert was issued by
World Health Organization
World Health Organization for the Americas. In August 2011,
according to the U.S. Geological Survey and the CDC, northern sea
otters off the coast of Washington state were infected with the same
version of the H1N1 flu virus that caused the 2009 pandemic and "may
be a newly identified animal host of influenza viruses". In May 2013,
seventeen people died during an H1N1 outbreak in
Venezuela , and a
further 250 were infected. As of early January 2014, Texas health
officials have confirmed at least thirty-three H1N1 deaths and
widespread outbreak during the 2013/2014 flu season, while twenty-one
more deaths have been reported across the US. Nine people have been
reported dead from an outbreak in several Canadian cities, and Mexico
reports outbreaks resulting in at least one death. Spanish health
authorities have confirmed 35 H1N1 cases in the Aragon region, 18 of
whom are in intensive care. On March 17, 2014, three cases were
confirmed with a possible fourth awaiting results occurring at the
Centre for Addiction and Mental Health in
Toronto , Ontario, Canada.
2015 INDIA OUTBREAK
2015 Indian swine flu outbreak
Swine flu was reported in India in early 2015. The disease affected
more than 31,000 people and claimed over 1,900 lives.
2017 MALDIVES OUTBREAK
Maldives reported Swine flu in early 2017. 501 people were tested
for the disease; 185 (37%) of those tested were positive for the
disease. 4 people from these 185 died due to this disease.
The total number of people who have died due to the disease is
unknown. Patient zero was never identified.
Schools were closed for a week due to the disease, but were ordered
by the Ministry of Education to open after the holidays even though
the disease was not fully under control.
After widespread rumors about Saudi Arabia going to purchase an
entire atoll from Maldives, Saudi Arabian embassy in Maldives issued a
statement against the rumors. However the trip of the Saudi
monarch was going forward until it was cancelled later due to the H1N1
outbreak in Maldives.
2017 MYANMAR OUTBREAK
Myanmar reported H1N1 in late July 2017. As of 27 July, 30 confirmed
cases and 6 people had died. The Ministry of Health and Sports of
Myanmar sent official request to
WHO to provide help to control the
virus; and also mentioned that government would be seeking
international assistance, including from the UN, China and the United
Pregnant women who contract the H1N1 infection are at a greater risk
of developing complications because of hormonal changes, physical
changes and changes to their immune system to accommodate the growing
fetus. For this reason the Center for
Disease Control and Prevention
recommends that those who are pregnant to get vaccinated to prevent
the influenza virus. The vaccination should not be taken by people who
have had a severe allergic reaction to the influenza vaccination.
Additionally those who are moderately to severely ill, with or without
a fever should wait until they recover before taking the vaccination.
Pregnant women who become infected with the influenza are advised to
contact their doctor immediately.
Influenza can be treated using
antiviral medication, which are available by prescription. Oseltamivir
(trade name Tamiflu) and zanamivir (Relenza) are two neuraminidase
inhibitors (antiviral medications) currently recommended. It has been
shown that they are most effective when taken within two days of
Since October 1, 2008, the CDC has tested 1,146 seasonal influenza A
(H1N1) viruses for resistance against oseltamivir and zanamivir. It
was found that 99.6% of the samples were resistant to oseltamivir
while none were resistant to zanamivir. In 853 samples of 2009
Influenza A (H1N1) virus only 4% showed resistance to oseltamivir,
while none of 376 samples showed resistance to zanamivir. A study
conducted in Japan during the 2009 H1N1 pandemic concluded that
infants exposed to either oseltamivir or zanamivir had no short term
adverse effects. Both amantadine and rimantadine have been found to
be teratogenic and embryotoxic (malformations and toxic effects on the
embryo) when given at high doses in animal studies.
Wikimedia Commons has media related to H1N1 .
Wikimedia Commons has media related to H1N1 SUBTYPE INFLUENZA A
This colorized transmission electron micrograph shows H1N1 influenza
virus particles. Surface proteins on the virus particles are shown in
This colorized transmission electron micrograph shows H1N1 influenza
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