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Influenza
*** Shopping-Tip: Influenza
{{Flu}}
'''Influenza''', commonly known as the '''flu''' or the '''grippe''', is a contagious
disease of the upper airways and the
lungs, caused by an
RNA virus of the
orthomyxoviridae family. It rapidly spreads around the world in seasonal
epidemics, killing millions of people in pandemic years and hundreds of thousands in nonpandemic years. It creates health care costs and lost productivity. Three influenza
pandemics in the
20th century 20th century, each following a major genetic change in the
virus, killed millions of people all over the world.
It is not connected to
gastroenteritis, which is commonly known as "stomach flu" or the "24 hour flu".
The term influenza has its origins in 15th century Italy, where the cause of the disease was ascribed to unfavourable
astrology astrological ''influences''.
Evolution in medical thought led to its modification to "influenza di freddo", meaning "influence of the cold", which by the 18th century became the prevalent terminology in the English-speaking world as well.
Image:Influenza_virus.png Hong Kong Flu.html" title="Meaning of frame frame|Negatively stained flu virions. These were the causative agent of the [[Hong Kong Flu pandemic..html" title="Meaning of Negatively stained flu virions. These were the causative agent of the [[Hong Kong Flu">frame|Negatively stained flu virions. These were the causative agent of the [[Hong Kong Flu pandemic.">Negatively stained flu virions. These were the causative agent of the [[Hong Kong Flu">frame|Negatively stained flu virions. These were the causative agent of the [[Hong Kong Flu pandemic.
History
{{see also|influenza pandemic}}
The most known outbreaks are caused by
antigenic shift, when two strains of influenza recombine forming a lethal new strain. The most famous outbreak (and the most lethal) was the so-called
Spanish Flu pandemic (
avian influenza type A influenza,
H1N1 strain), which lasted from
1918 to
1919, and is believed to have killed more people in total than
World War I. While the war casualties accumulated over several years, the pandemic took most of its toll over a period of weeks. Lesser flu epidemics included the
1957 Asian Flu (type A,
H2N2 strain) and the
1968 Hong Kong Flu (type A,
H3N2 strain).
;Known flu pandemics
[[http://biomicro.sdstate.edu/WangX/Micr425/Pathogenesis/Influenza_A.pdf Influenza PDF]]
*
1889-
1890 90 - Asiatic (Russian) Flu, mortality rate said to be 0.75-1 death per 1000 possibly
H2N2
*
1900 - possibly
H3N8
*
1918–
1920 20 –
Spanish flu Spanish Flu, 500 million ill, at least 40 million died of
H1N1
*
1957–
1958 58 –
Asian Flu, 1 to 1.5 million died of
H2N2
*
1968–
1969 69 –
Hong Kong Flu, 3/4 to 1 million died of
H3N2
Although there were scares in
New Jersey in
1976 (the
Swine Flu), worldwide in
1977 (the
Russian Flu), and in
Hong Kong (as well as in other Asian countries, namely continental China, as became known later) in
1997 (
Avian influenza), there have been no major pandemics subsequent to the 1968 infection. Increased immunity from
antibody antibodies, and the development of
flu vaccines have limited the spread of the virus, and so far prevented any further pandemics.
Symptoms
The virus attacks the
respiratory system respiratory tract, is transmitted from person to person by saliva droplets expelled by coughing, and causes the following
symptoms:
*
Fever
*
Headache
* Fatigue/Sore joints (can be extreme)
* Dry cough
* Sore throat
*
Nasal congestion
*
Sneezing
* Irritated eyes
* Body aches
* Extreme coldness
Influenza's effects are much more severe than those of the "
common cold cold", and last longer. Recovery takes about one to two weeks. Influenza can be deadly, especially for the weak, old or chronically ill. Some flu
Pandemic pandemics have killed millions of people.
Most people who get influenza will recover in one to two weeks, but others will develop life-threatening complications (such as
pneumonia). Millions of people in the
United States (about 10% to 20% of U.S. residents) are infected with influenza each year. An average of about 36,000 people per year in the United States die from influenza, and 114,000 per year are admitted to a hospital as a result of influenza. According to estimates by the
World Health Organization, between 250,000 and 500,000 die from influenza infection each year worldwide. Even healthy people can be affected, and serious problems from influenza can happen at any age. People age 65 years and older, people of any age with chronic medical conditions, and very young children are more likely to get complications from influenza.
Pneumonia,
bronchitis,
sinus, and
ear infections are four examples of such complications.
The flu can make chronic health problems worse. For example, people with asthma may experience
asthma attacks while they have the flu, and people with chronic
congestive heart failure may have a worsening of this condition, that is triggered by the flu.
Flu season
{{main|Flu season}}
Influenza reaches peak prevalence in
winter, and because the
Northern Hemisphere Northern and
Southern Hemisphere have winter at different times of the year, there are actually two flu seasons each year. Therefore, the
World Health Organization (assisted by the
National Influenza Centers) makes two
vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere.
While most influenza outbreaks in the Northern Hemisphere tend to peak in January or February, not all do. For example, the
Spanish_Flu influenza pandemic of 1918 and 1919 reached peak virulence during late spring and summer worldwide, and not until October in the US. It remains unclear why outbreaks of the flu occur seasonally rather than uniformly throughout the year.
One possible explanation is that, because people are indoors more often during the winter, they are in close contact more often, and this promotes transmission from person to person. Another is that cold temperatures lead to drier air, which may dehydrate mucus, preventing the body from effectively expelling virus particles. The virus may also linger longer on exposed surfaces (doorknobs, countertops, etc.) in colder temperatures. Increased travel and visitation due to the holiday season may also play a role.
[[http://www.npr.org/templates/story/story.php?storyId=1551913 NPR]]
Prevention
It is possible and in many cases recommended to get vaccinated against influenza with a
flu vaccine. However, due to the high mutability of the virus, a particular flu vaccine formulation usually only works for about a year. The
World Health Organization co-ordinates the contents of the vaccine each year to contain the most likely strains of the virus which probably will attack the next year. The flu vaccine is usually recommended for anyone in a high-risk group who would be likely to suffer complications from influenza. Flu vaccine is available as
nasal spray vaccine (recommended for all healthy people ages 5 to 49) and as injectable vaccine.
It is possible to get vaccinated for the season and still catch the flu. The vaccine is reformulated each season for a few specific flu strains, but cannot possibly include all the different strains actively infecting people in the world for that season. This means that you could catch a virus not covered by the vaccine. Also, it takes about six months for the manufacturers to formulate and make the millions of doses required to deal with the seasonal epidemics; occasionally a new or overlooked strain becomes prominent during that six months and infects people even though they've been vaccinated (as in the 2003-2004 season). The vaccine may have partial coverage for these unexpected strains. It is also possible to get infected and then get vaccinated the next day, before flu symptoms appear, and still get sick with the very strain that the vaccine is supposed to prevent. The vaccine can take a few days to become effective.
Vaccines can cause the immune system to react as if the body were actually being infected, and general infection symptoms (many cold and flu symptoms are just general infection symptoms) can appear, though these symptoms are usually not as severe or as long lasting as the flu.
"The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. The risk of a flu shot causing serious harm, or death, is extremely small. However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions. Almost all people who get influenza vaccine have no serious problems from it."
[[http://www.cdc.gov/flu/about/qa/flushot.htm CDC]]
Influenza pandemic#Personal health and hygiene Personal health and hygiene are important in avoiding and minimizing influenza.
Treatment
:''See main article:
Flu treatment''
If you get the flu, get plenty of rest, drink a lot of liquids, and avoid using alcohol and tobacco. You can take medications such as
acetaminophen to relieve the fever and muscle aches associated with the flu. Children and teenagers with flu symptoms (particularly fever) should avoid taking
aspirin as taking aspirin in the presence of influenza infection (especially
Influenzavirus B influenza type B) can lead to
Reye syndrome, a rare but potentially fatal disease of the
liver.
[[http://www.cdc.gov/ncidod/diseases/reye.htm CDC]]
During the
2005-
2006 flu season in the
United States,
CDC encourages the use of
oseltamivir for flu prevention and the use of
oseltamivir or
zanamivir for flu treatment.
[[http://www.cdc.gov/flu/professionals/treatment/0506antiviralguide.htm CDC]]
The
CDC says:
:Three antiviral drugs (
amantadine,
rimantadine, and
oseltamivir) are approved for use in preventing the flu. These are prescription medications, and a doctor should be consulted before they are used. During the
2005-
2006 influenza season, CDC recommends against the use of amantadine or rimantadine for the treatment or
prophylaxis of influenza in the
United States.
[[http://www.cdc.gov/flu/symptoms.htm CDC]]
The annual flu (also called "seasonal flu" or "human flu") kills an estimated 36,000 people in the
United States each year. The annually updated trivalent
flu vaccine consists of
hemagglutinin (HA) surface glycoprotein components from influenza
H3N2,
H1N1, and
Influenzavirus B B influenza viruses.
[[http://www.cdc.gov/ncidod/EID/vol11no08/05-0302.htm CDC]] The dominant strain in
January 2006 is
H3N2. 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..html Reason] [http://www.nytimes.com/2006/01/15/health/15drugs.html New York Times]]
Variability
{{H5N1}}
Influenza is an extremely variable disease and is also found in pigs (''swine flu''), birds (''bird flu''), and other animals. In areas where there are high concentrations of humans, pigs and birds in close proximity, such as parts of Asia, simultaneous infections across species enable genetic material to be exchanged between the various strains of flu. It is believed that sooner or later, a recombination may occur to produce a strain as lethal as the
1918 virus. In late
1997, a new strain of
avian influenza (also known as ''bird flu'') called
H5N1 infected 18 people in Hong Kong, of whom 6 died.
Avian influenza
{{main|Avian influenza}}
Genetic reassortment ("mixing") of a human flu virus with the current
H5N1 avian influenza has been identified as the most likely source of the next pandemic.
The natural host for influenza virus is aquatic
birds. Pandemic influenza often occurs when an avian-adapted virus infects a
porcine host, which can be infected by human and avian varieties of influenza A virus. The
virus may then recombine within the
pig, to form a genetically new virus which is able to infect humans and be transmitted from person to person.
The current avian flu threat is due to the
H5N1 virus. It is thought likely that the virus will eventually become adapted and able to spread from person to person. If this happens, a
pandemic may be unavoidable, since there will be very little immunity to this genetically new virus, and international travel coupled with densely populated cities will spread the virus rapidly.
Currently, governments are stockpiling anti-viral drugs such as
oseltamivir, which can reduce the effects of the virus. It is difficult to design a
vaccine for the virus until it has changed into a human adapted form, but if a
pandemic does occur a vaccine will be required urgently.
How H5N1 kills
H5N1 is a
virus. It has eight
RNA molecules in each
virion. The exact molecular makeup of hundreds of genotypes (variants) of both H5N1 and other
Influenzavirus A avian flu viruses are known.
The NS RNA molecule codes for two proteins called NS1 and NEP.
The NS1
protein of the highly pathogenic avian
H5N1 viruses circulating in
poultry and
waterfowl in Southeast
Asia is currently believed to be responsible for an enhanced proinflammatory
cytokine response. H5N1 NS1 is characterized by a single
amino acid change at position 92. By changing the amino acid from
glutamic acid to
aspartic acid, researchers were able to abrogate the effect of the H5N1 NS1. This single amino acid change in the NS1 gene greatly increased the
pathogenicity of the H5N1 influenza virus.
In short, this one amino acid difference in the NS1 protein produced by the NS
RNA molecule of the
H5N1 virus is believed to be largely responsible for an increased
pathogenicity (on top of the already increased pathogenicity of its hemagglutinin type which allows it to grow in organs other than lungs) that can manifest itself by causing a
cytokine storm in a patient's body, often causing
pneumonia and
death.
Other important mechanisms also exist "in the acquisition of virulence in
Influenzavirus A avian influenza viruses".
[[http://www.cdc.gov/ncidod/EID/vol10no12/04-0743.htm CDC]]
Research
:''See also:
Flu vaccine#H5N1 and
Influenza pandemic#Strategies to slow down a pandemic''
Influenza research includes
molecular virology,
pathogenesis, host
immune responses, and
epidemiology. These help in developing influenza countermeasures such as
vaccines, therapies and diagnostic tools.
Improved influenza countermeasures require basic research on how viruses enter cells, replicate, mutate, evolve into new strains and induce an immune response.
The
Influenza Genome Sequencing Project is creating a library of influenza sequences that will help us understand what makes one strain more lethal than another, what genetic determinants most affect immunogenicity, and how the virus evolves over time.
Solutions to limitations in current vaccine methods are being researched. The US government has purchased from
Sanofi Pasteur and
Chiron Corporation several million doses of
vaccine meant to be use in case of an
influenza pandemic from
H5N1 and is conducting clinical trials on them.
[ [http://www.nytimes.com/2006/03/30/health/30vaccine.html?_r=1&oref=slogin New York Times article ""Doubt Cast on Stockpile of a Vaccine for Bird Flu""]] ABC News reported on April 1, 2006 that "Beginning in late 1997, the human trials have tested 30 different vaccines, all pegged to the H5N1 virus."
[[http://www.abcnews.go.com/WNT/AvianFlu/story?id=1794656&page=1]]
A technique called
reverse genetics allows scientists to manipulate the genomes of influenza viruses and to transfer genes between viral strains. The technique allows the rapid generation of seed viruses for vaccine candidates that exactly match the anticipated epidemic strain. By removing or modifying certain virulence genes, reverse genetics also can be used to convert highly pathogenic influenza viruses into vaccine candidates that are safer for vaccine manufacturers to handle.
Another technique is use of
cell cultures to grow vaccine strains; such as genetically engineering
baculovirus to express a gene that encodes an influenza coat protein such as
hemagglutinin or
neuraminidase. "A recent NIAID-supported Phase II clinical trial of a vaccine produced by Protein Sciences Corporation using this strategy showed that it is well tolerated and immunogenic; the company is conducting further clinical evaluation of this product. Other new pathways for producing influenza vaccines include DNA-based approaches and the development of broadly protective vaccines based on influenza virus proteins that are shared by multiple strains."
[[http://www.hhs.gov/asl/testify/t041118.html The NIH Biomedical Research Response to Influenza]]
"To address the
H9N2 threat,
NIAID contracted with
Chiron Corporation to produce investigational batches of an inactivated vaccine, which will be evaluated clinically by
NIAID early next year. For
H5N1,
Aventis-Pasteur, Inc. and Chiron are both producing investigational lots of inactivated H5N1 vaccine preparations; additionally,
DHHS has contracted with Aventis to produce up to 2 million doses to be stockpiled for emergency use, if needed, to vaccinate health workers, researchers, and, if indicated, the public in affected areas. Development and evaluation of a combination antiviral regimen against these potential pandemic influenza strains are also now under way."
has evidence of inhibition of multiple subtypes of
influenza A virus in
cell culture with
Morpholino oligomers from the results of their labs and four independent research laboratories. "The key finding here is that our NEUGENE(R) therapeutics continue to show efficacy against all strains of influenza A, including
H5N1."
[ [http://www.genengnews.com/news/bnitem.aspx?name=1203972XSL_NEWSML_TO_NEWSML.xml AVI BioPharma Reports Successful Inhibition of Multiple Subtypes of Influenza A Using NEUGENE Antisense Therapeutic]]
Sources
* Special Issue: Influenza (>20 articles). [http://www.cdc.gov/ncidod/EID/vol12no01/contents_v12n01.htm Emerging Infectious Diseases], January 2006.
* WHO 2005. The Writing Committee of the World Health Organization (WHO). Avian influenza A (H5N1) infection in humans. N Engl J Med 2005; 353: 1374-85. – [http://content.nejm.org/cgi/content/extract/353/13/1374 Full text].
* CDC 2005. Centers for Disease Control. Prevention and Control of Influenza Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2005; 54 (RR08): 1-40. - [http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5408a1.htm Full text].
* Moscona A. Neuraminidase inhibitors for influenza. N Engl J Med 2005; 353: 1363-73. – [http://content.nejm.org/cgi/content/full/353/13/1363 Full text].
* Osterholm MT. Preparing for the next pandemic. N Engl J Med 2005; 352: 1839-42. - [http://content.nejm.org/cgi/content/full/352/18/1839 Full text].
-
CDC info on influenza
-
World Health Organization Fact Sheet Overview of influenza.
-
NHS Direct Health encyclopedia entry
Further reading
-
Influenza Report 2006 Online book. Research level information. Highly recommended.
-
Medicine Net's overview of influenza
-
CDC Information About Influenza Pandemics.
-
Congressional Research Service (CRS) Reports regarding Influenza Law related government reports.
-
WHO Avian influenza frequently asked questions.
-
A guide to bird flu and its symptoms from BBC Health.
-
FIC, flu in china & flu information center (bilingual, with forums).
-
The Avian Flu Information Site - Layperson's information about avian flu, its history and preventative measures.
-
Influenza Surveillance and Contingency Plans (by Country/Region)
-
CIDRAP - Avian Influenza (an excellent collection of information; news links, lab confirmed count of cases, suggested reading, etc)
-
Multiple resources on Avian Influenza from Iowa State University
-
Bird Flu and the Law,
JURIST
-
Latest Bird Flu news and articles
-
Wildlife Disease Information Node - Avian Influenza information for the wildlife perspective
-
Avian Influenza News from the USGS National Wildlife Health Center
-
Avian Flu Preparedness Guide - from The Center for Technology and National Security Policy
-
Fuss and Feathers: Pandemic Panic over the Avian Flu
Category:Poultry diseases
Category:Animal diseases
Category:Influenza *
{{Link FA|pt}}
ar:Ù?يروس إنÙ?لونزا
bg:Грип
zh-min-nan:Liû-hêng-sèng kám-mÅ?·
cs:Chřipka
cy:Y ffliw
da:Influenza
de:Influenza
es:Gripe
eo:Gripo
eu:Gripe
fa:آنÙ?لوآنزا
fr:Grippe
gl:Gripe
ko:�플루엔�
hr:Gripa
io:Influenzo
id:Influensa
it:Influenza
he:שפעת
nl:Griep
ja:インフルエンザ
no:Influensa
pl:Grypa
pt:Gripe
ru:Грипп
sq:Gripi
sl:Gripa
fi:Influenssa
sv:Influensa
tr:Grip
zh:�行性感冒
Category:Infectious diseases
Category:Viruses
fr:Catégorie:Grippe
ko:분류:�플루엔�
sl:Kategorija:Gripa
vi:Thể loại:Cúm
tr:Kategori:Grip
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