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In humans, influenza's effects are much more severe than those of the [[common cold]], and last longer. Recovery takes about one to two weeks. Influenza, however, can be deadly, especially for the weak, old or chronically ill.<ref name=Hilleman/>
In humans, influenza's effects are much more severe than those of the [[common cold]], and last longer. Recovery takes about one to two weeks. Influenza, however, can be deadly, especially for the weak, old or chronically ill.<ref name=Hilleman/>


===Symptoms===
==[[History & Symptoms]]==
Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills or a chilly sensation but fever is also common early in the infection, with body temperatures as high as 39 °C (approximately 103 °F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worst in their backs and legs.<ref name=Merck />
 
Common symptoms of the flu such as fever, headaches, and fatigue come from the huge amounts of proinflammatory [[cytokine]]s and [[chemokine]]s (such as [[interferon]] or [[Tumor necrosis factor-alpha|tumor necrosis factor]]) produced from influenza-infected cells.<ref name=Eccles/><ref>{{cite journal | author = Schmitz N, Kurrer M, Bachmann M, Kopf M | title = Interleukin-1 is responsible for acute lung immunopathology but increases survival of respiratory influenza virus infection. | journal = J Virol | volume = 79 | issue = 10 | pages = 6441–8 | year = 2005 | id = PMID 15858027}}</ref> In contrast to the [[rhinovirus]] that causes the [[common cold]], influenza does cause tissue damage, so symptoms are not entirely due to the inflammatory response.<ref>{{cite journal | author = Winther B, Gwaltney J, Mygind N, Hendley J | title = Viral-induced rhinitis. | journal = Am J Rhinol | volume = 12 | issue = 1 | pages = 17–20 | year = | id = PMID 9513654}}</ref> Symptoms of influenza may include:
 
:* Body aches, especially joints and throat
:* [[Cough]]ing and [[sneeze|sneezing]]
:* Extreme coldness and [[fever]]
:* [[Fatigue (medical)|Fatigue]]
:* [[Headache]]
:* Irritated watering eyes
:* [[Nasal congestion]]
:* [[Nausea]] and [[vomiting]]
:* Reddened eyes, skin (especially face), mouth, throat and nose
 
It can be difficult to distinguish between the common cold and influenza in the early stages of these infections,<ref name=Eccles/> but usually the symptoms of the flu are more severe than their common-cold equivalents.  Research on signs and symptoms of influenza found that the best findings for excluding the diagnosis of influenza were:<ref name="pmid15728170">{{cite journal | author = Call S, Vollenweider M, Hornung C, Simel D, McKinney W | title = Does this patient have influenza? | journal = JAMA | volume = 293 | issue = 8 | pages = 987-97 | year = 2005 | doi = 10.1001/jama.293.8.987 | id = PMID 15728170}}</ref>
 
{| class="wikitable" style="text-align:center"
|+ Highest  [[sensitivity (tests)|sensitive]] individual findings for diagnosing influenza<ref name="pmid15728170"/>
! Finding: !! [[sensitivity (tests)|sensitivity]] !! [[specificity (tests)|specificity]]
|-
! Fever
| 86% || 25%
|-
! Cough
| 98% || 23%
|-
! Nasal congestion
| 70–90% || 20–40%
|-
|}
Notes to table:
* [[Sensitivity (tests)|Sensitivity]] is the proportion of people that tested positive of all the positive people tested.
* [[Specificity (tests)|Specificity]]  is the proportion of people that tested negative of all the negative people tested.
* All three findings, especially fever, were less sensitive in patients over 60 years of age.
 
Since anti-viral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. Of the symptoms listed above, the combinations of findings below can improve diagnostic accuracy.<ref name="pmid11088084">{{cite journal | author = Monto A, Gravenstein S, Elliott M, Colopy M, Schweinle J | title = Clinical signs and symptoms predicting influenza infection. | journal = Arch Intern Med | volume = 160 | issue = 21 | pages = 3243–7 | year = 2000 | url http://archinte.ama-assn.org/cgi/content/abstract/160/21/3243 | id = PMID 11088084}}</ref> Unfortunately, even combinations of findings are imperfect. However, [[Bayes Theorem]] can combine pretest probability with clinical findings to adequately diagnose or exclude influenza in some patients. The pretest probability has a strong seasonal variation; the current prevalence of influenza among patients in the United States receiving sentinel testing is available at the [[Centers for Disease Control and Prevention|CDC]].<ref>Centers for Disease Control and Prevention.  [http://www.cdc.gov/flu/weekly/ Weekly Report: Influenza Summary Update.] Accessed January 1, 2007.</ref>  Using the CDC data, the following table shows how the likelihood of influenza varies with prevalence:
:
 
<table border="1" cellpadding="5" class="wikitable">
<caption>Combinations of findings for diagnosing influenza<ref name="pmid15728170"/></caption>
  <tr>
    <th rowspan="2">Combinations of findings </th>
    <th rowspan="2">Sensitivity</th>
    <th rowspan="2">Specificity</th>
    <th colspan="2"><p>As reported in study<ref name="pmid15728170">.</ref><br/>and projected during local outbreaks<br/>
      (prevalence= 66%)</p>
    </th>
    <th colspan="2">Projected during influenza season <br/>
    (prevalence=25%)</th>
    <th colspan="2">Projected in off-season<br/>
      (prevalence=2%) </th>
  </tr>
  <tr>
    <th>PPV</th>
    <th>NPV</th>
    <th>PPV</th>
    <th>NPV</th>
    <th>PPV</th>
    <th>NPV</th>
  </tr>
  <tr>
    <td>Fever and cough</td>
    <td align="center">64%</td>
    <td align="center">67%</td>
    <td align="center">79%</td>
    <td align="center">49%</td>
    <td align="center">39%</td>
    <td align="center">15%</td>
    <td align="center">4%</td>
    <td align="center">1%</td>
  </tr>
  <tr>
    <td>Fever and cough and sore throat</td>
    <td align="center">56</td>
    <td align="center">71</td>
    <td align="center">79</td>
    <td align="center">45</td>
    <td align="center">39</td>
    <td align="center">17</td>
    <td align="center">4</td>
    <td align="center">2</td>
  </tr>
  <tr>
    <td>Fever and cough and nasal congestion</td>
    <td align="center">59</td>
    <td align="center">74</td>
    <td align="center">81</td>
    <td align="center">48</td>
    <td align="center">43</td>
    <td align="center">16</td>
    <td align="center">4</td>
    <td align="center">1</td>
  </tr>
</table>
 
Two [[decision analysis]] studies<ref name="pmif12361816">{{cite journal | author = Smith K, Roberts M | title = Cost-effectiveness of newer treatment strategies for influenza. | journal = Am J Med | volume = 113 | issue = 4 | pages = 300-7 | year = 2002 | doi = 10.1016/S0002-9343(02)01222-6 | id = PMID 12361816}}</ref><ref name="pimd12965940">{{cite journal | author = Rothberg M, Bellantonio S, Rose D | title = Management of influenza in adults older than 65 years of age: cost-effectiveness of rapid testing and antiviral therapy. | journal = Ann Intern Med | volume = 139 | issue = 5 Pt 1 | pages = 321-9 | year = 2003 | url = http://www.annals.org/cgi/content/abstract/139/5_Part_1/321 | id = PMID 12965940}}</ref> suggest that ''during local outbreaks'' of influenza, the prevalence will be over 70%<ref name="pimd12965940"/> and thus patients with any of the above combinations of symptoms may be treated with neuramidase inhibitors without testing. Even in the absence of a local outbreak, treatment may be justified in the elderly during the influenza season as long as the prevalence is over 15%.<ref name="pimd12965940"/>
 
Most people who get influenza will recover in one to two weeks, but others will develop life-threatening complications (such as [[pneumonia]]). According to the [[World Health Organization]]: "Every winter, tens of millions of people get the flu. Most are home, sick and miserable, for about a week. Some—mostly the elderly—die. We know the world-wide death toll exceeds a few hundred thousand people a year, but even in developed countries the numbers are uncertain, because medical authorities don't usually verify who actually died of influenza and who died of a flu-like illness."<ref>Peter M. Sandman and Jody Lanard [http://www.paho.org/English/DD/PIN/Number22_article1a.htm "Bird Flu: Communicating the Risk"] 2005 ''Perspectives in Health Magazine'' Vol. 10 issue 2.</ref> Even healthy people can be affected, and serious problems from influenza can happen at any age. People over 50 years old, very young children and people of any age with chronic medical conditions, are more likely to get complications from influenza: such as pneumonia, [[bronchitis]], [[sinus]], and [[ear infection]]s.<ref name=CDCkeyfacts> [http://www.cdc.gov/flu/protect/keyfacts.htm Key Facts about Influenza (Flu) Vaccine] CDC publication. Published October 17, 2006. Accessed 18 Oct 2006.</ref>
 
The flu can worsen chronic health problems. People with emphysema, chronic bronchitis or asthma may experience shortness of breath while they have the flu, and influenza may cause worsening of [[coronary heart disease]] or [[congestive heart failure]].<ref>Angelo SJ, Marshall PS, Chrissoheris MP, Chaves AM. "Clinical characteristics associated with poor outcome in patients acutely infected with Influenza A." ''Conn Med.'' 2004 Apr;68(4):199–205. PMID 15095826</ref> [[Tobacco smoking|Smoking]] is another [[risk factor]] associated with more serious disease and increased mortality from influenza.<ref>{{cite journal | author = Murin S, Bilello K | title = Respiratory tract infections: another reason not to smoke. | journal = Cleve Clin J Med | volume = 72 | issue = 10 | pages = 916-20 | year = 2005 | id = PMID 16231688}}</ref>


===Laboratory tests===
===Laboratory tests===

Revision as of 22:02, 9 January 2012

Influenza Microchapters

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Differentiating Influenza from other Diseases

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History and Symptoms

Physical Examination

Laboratory Findings

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Influenza
TEM of negatively stained influenza virons, magnified approximately 70,000 times
ICD-10 J10, J11
ICD-9 487
DiseasesDB 6791
MedlinePlus 000080
MeSH D007251

Template:Flu

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Historical perspective

Classification

Diagnosis

Influenza spreads by aerosols created by coughs or sneezes.

In humans, influenza's effects are much more severe than those of the common cold, and last longer. Recovery takes about one to two weeks. Influenza, however, can be deadly, especially for the weak, old or chronically ill.[1]

History & Symptoms

Laboratory tests

The available laboratory tests for influenza continue to improve. The United States Centers for Disease Control and Prevention (CDC) maintains an up-to-date summary of available laboratory tests.[2] According to the CDC, rapid diagnostic tests have a sensitivity of 70–75% and specificity of 90–95% when compared with viral culture. These tests may be especially useful during the influenza season (prevalence=25%) but in the absence of a local outbreak, or peri-influenza season (prevalence=10%[3]).

Epidemiology

Seasonal variations

Cumulative Confirmed Human Cases of H5N1.[4] The regression curve for deaths is shown extended through the end of November 2006.

Influenza reaches peak prevalence in winter, and because the Northern and Southern Hemisphere have winter at different times of the year, there are actually two different flu seasons each year. This is why the World Health Organization (assisted by the National Influenza Centers) makes recommendations for two different vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere.[5]

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 survive longer on exposed surfaces (doorknobs, countertops, etc.) in colder temperatures. Increased travel and visitation due to the Northern Hemisphere winter holiday season may also play a role.[6] However, seasonal changes in infection rates are also seen in tropical regions and these peaks of infection are seen mainly during the rainy season.[7] Seasonal changes in contact rates from school-terms, which are a major factor in other childhood diseases such as measles and pertussis, may also play a role in flu. A combination of these small seasonal effects may be amplified by "dynamical resonance" with the endogenous disease cycles.[8] H5N1 exhibits seasonality in both humans and birds.[4]

An alternative hypothesis to explain seasonality in influenza infections is an effect of vitamin D levels on immunity to the virus.[9] This idea was first proposed by Robert Edgar Hope-Simpson in 1965.[10] He proposed that the cause of influenza epidemics during winter may be connected to seasonal fluctuations of vitamin D, which is produced in the skin under the influence of solar (or artificial) UV radiation. This could explain why influenza occurs mostly in winter and during the tropical rainy season, when people stay indoors, away from the sun, and their vitamin D levels fall. Furthermore, some studies have suggested that administering cod liver oil, which contains large amounts of vitamin D, can reduce the incidence of respiratory tract infections.[11]

Epidemic and pandemic spread

Antigenic drift creates influenza viruses with slightly-modified antigens, while antigenic shift generates viruses with entirely novel antigens.
How antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human influenza

As influenza is caused by a variety of species and strains of viruses, in any given year some strains can die out while others create epidemics while yet another strain can cause a pandemic. Typically, in a year's normal two flu seasons (one per hemisphere) there are between three and five million cases of severe illness and up to 500,000 deaths worldwide, which by some definitions is a yearly influenza epidemic.[12] Although the incidence of influenza can vary widely between years, approximately 36,000 deaths and more than 200,000 hospitalizations are directly associated with influenza every year in America.[13][14][15] Every ten to twenty years a pandemic occurs, which infects a large proportion of the world's population, and can kill tens of millions of people (see history section).

New influenza viruses are constantly being produced by mutation or by reassortment.[16] Mutations can cause small changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. This is called antigenic drift, which creates an increasing variety of strains over time until one of the variants eventually achieves higher fitness, becomes dominant, and rapidly sweeps through the human population – often causing an epidemic.[17] In contrast, when influenza viruses re-assort, they may acquire new antigens — for example by reassortment between avian strains and human strains; this is called antigenic shift. If a human influenza virus is produced with entirely novel antigens, everybody will be susceptible and the novel influenza will spread uncontrollably, causing a pandemic.[18] In contrast to this model of pandemics based on antigenic drift and shift, an alternative approach has been proposed where the periodic pandemics are produced by interactions of a fixed set of viral strains with a human population with a constantly-changing set of immunities to different viral strains.[19]

Prevention

Vaccination and infection control

U.S. Navy personnel receiving influenza vaccination

Vaccination against influenza with a flu vaccine is strongly recommended for high-risk groups, such as children and the elderly.

Flu vaccines can be produced in several ways; the most common method is to grow the virus in fertilised hen eggs. After purification, the virus is inactivated (for example, by treatment with detergent) to produce an inactivated-virus vaccine. Alternatively, the virus can be grown in eggs until it loses virulence and the avirulent virus given as a live vaccine.[1] The effectiveness of these flu vaccines is variable. Due to the high mutation rate of the virus, a particular flu vaccine usually confers protection for no more than a few years. Every year, the World Health Organization predicts which strains of the virus are most likely to be circulating in the next year, allowing pharmaceutical companies to develop vaccines that will provide the best immunity against these strains.[5] Vaccines have also been developed to protect poultry from avian influenza. These vaccines can be effective against multiple strains and are used either as part of a preventative strategy, or combined with culling in attempts to eradicate outbreaks.[20]

It is possible to get vaccinated and still get influenza. The vaccine is reformulated each season for a few specific flu strains, but cannot possibly include all the strains actively infecting people in the world for that season. It takes about six months for the manufacturers to formulate and produce the millions of doses required to deal with the seasonal epidemics; occasionally, a new or overlooked strain becomes prominent during that time and infects people although they have been vaccinated (as by the H3N2 Fujian flu in the 2003–2004 flu season).[21] It is also possible to get infected just before vaccination and get sick with the very strain that the vaccine is supposed to prevent, as the vaccine takes about two weeks to become effective.[22]

The 2006–2007 season is the first in which the CDC has recommended that children younger than 59 months receive the annual flu vaccine.[23] 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 long-lasting as influenza. The most dangerous side-effect is a severe allergic reaction to either the virus material itself, or residues from the hen eggs used to grow the influenza; however, these reactions are extremely rare.[24]

Good personal health and hygiene habits are reasonably effective in avoiding and minimizing influenza. People who contract influenza are most infective between the second and third days after infection and infectivity lasts for around 10 days.[25] Children are notably more infectious than adults, and shed virus from just before they develop symptoms until 2 weeks after infection.[25][26]

Since influenza spreads through aerosols and contact with contaminated surfaces, it is important to persuade people to cover their mouths while sneezing and to wash their hands regularly.[23] Surface sanitizing is recommended in areas where influenza may be present on surfaces.[27] Alcohol is an effective sanitizer against influenza viruses, while quaternary ammonium compounds can be used with alcohol, to increase the duration of the sanitizing action.[28] In hospitals, quaternary ammonium compounds and halogen-releasing agents such as sodium hypochlorite are commonly used to sanitize rooms or equipment that have been occupied by patients with influenza symptoms.[28] During past pandemics, closing schools, churches and theaters slowed the spread of the virus but did not have a large effect on the overall death rate.[29][30]

Treatment

People with the flu are advised to get plenty of rest, drink a lot of liquids, avoid using alcohol and tobacco and, if necessary, take medications such as paracetamol (acetaminophen) to relieve the fever and muscle aches associated with the flu. Children and teenagers with flu symptoms (particularly fever) should avoid taking aspirin during an influenza infection (especially influenza type B) because doing so can lead to Reye's syndrome, a rare but potentially fatal disease of the liver.[31] Since influenza is caused by a virus, antibiotics have no effect on the infection; unless prescribed for secondary infections such as bacterial pneumonia, they may lead to resistant bacteria. Antiviral medication is sometimes effective, but viruses can develop resistance to the standard antiviral drugs.

The two classes of anti-virals are neuraminidase inhibitors and M2 inhibitors (adamantane derivatives). Neuraminidase inhibitors are currently preferred for flu virus infections. The CDC recommended against using M2 inhibitors during the 2005–06 influenza season.[32]

Neuraminidase inhibitors

Antiviral drugs such as oseltamivir (trade name Tamiflu) and zanamivir (trade name Relenza) are neuraminidase inhibitors that are designed to halt the spread of the virus in the body.[33] These drugs are often effective against both influenza A and B.[34] The Cochrane Collaboration reviewed these drugs and concluded that they reduce symptoms and complications.[35] Different strains of influenza virus have differing degrees of resistance against these antivirals and it is impossible to predict what degree of resistance a future pandemic strain might have.[36]

M2 inhibitors (adamantanes)

The antiviral drugs amantadine and rimantadine are designed to block a viral ion channel and prevent the virus from infecting cells. These drugs are sometimes effective against influenza A if given early in the infection, but are always ineffective against influenza B.[34] Measured resistance to amantadine and rimantadine in American isolates of H3N2 has increased to 91% in 2005.[37]

Research

CDC scientist working on influenza under high bio-safety conditions

Research on influenza includes studies on molecular virology, how the virus produces disease (pathogenesis), host immune responses, viral genomics, and how the virus spreads (epidemiology). These studies help in developing influenza countermeasures; for example, a better understanding of the body's immune response helps vaccine development, and a detailed picture of how influenza invades cells aids the development of antiviral drugs. One important basic research program is the Influenza Genome Sequencing Project, which is creating a library of influenza sequences; this library should help clarify which factors make one strain more lethal than another, which genes most affect immunogenicity, and how the virus evolves over time.[38]

Research into new vaccines is particularly important: as current vaccines are slow and expensive to produce and must be reformulated every year. The sequencing of the influenza genome and recombinant DNA technology may accelerate the generation of new vaccine strains by allowing scientists to substitute new antigens into a previously-developed vaccine strain.[39] New technologies are also being developed to grow virus in cell culture; which promises higher yields, less cost, better quality and surge capacity.[40] The U.S. government has purchased from Sanofi Pasteur and Chiron Corporation several million doses of vaccine meant to be used in case of an influenza pandemic of H5N1 avian influenza and is conducting clinical trials with these vaccines.[41] The UK government is also stockpiling millions of antiviral drugs(tamiflu, oseltamivir, zanimivir) to give to its citizens in the event of an outbreak, the UK Health Protection Agency has also gathered a limited amount of HPAI H5N1 vaccines for experimental purposes.

Infection in other animals

Template:H5N1

Influenza infects many animal species and transfer of viral strains between species can occur. Birds are thought to be the main animal reservoirs of influenza viruses.[42] Sixteen forms of hemagglutinin and 9 forms of neuraminidase have been identified. All known subtypes (HxNy) are found in birds but many subtypes are endemic in humans, dogs, horses, and pigs; populations of camels, ferrets, cats, seals, mink, and whales also show evidence of prior infection or exposure to influenza.[43] Variants of flu virus are sometimes named according to the species the strain is endemic in or adapted to. The main variants named using this convention are: Bird flu, Human Flu, Swine Flu, Horse Flu and Dog Flu. (Cat flu generally refers to Feline viral rhinotracheitis or Feline calicivirus and not infection from an influenza virus.) In pigs, horses and dogs, influenza symptoms are similar to humans, with cough, fever and loss of appetite.[43] The frequency of animal diseases are not as well-studied as human infection, but an outbreak of influenza in harbour seals caused approximately 500 seal deaths off the New England coast in 1979–1980.[44] On the other hand, outbreaks in pigs are common and do not cause severe mortality.[43]

Flu symptoms in birds are variable and can be unspecific.[45] The symptoms following infection with low-pathogenicity avian influenza may be as mild as ruffled feathers, a small reduction in egg production, or weight loss combined with minor respiratory disease.[46] Since these mild symptoms can make diagnosis in the field difficult, tracking the spread of avian influenza requires laboratory testing of samples from infected birds. Some strains such as Asian H9N2 are highly virulent to poultry, and may cause more extreme symptoms and significant mortality.[47] In its most highly pathogenic form, influenza in chickens and turkeys produces a sudden appearance of severe symptoms and almost 100% mortality within two days.[48] As the virus spreads rapidly in the crowded conditions seen in the intensive farming of chickens and turkeys, these outbreaks can cause large economic losses to poultry farmers.

An avian-adapted, highly pathogenic strain of H5N1 (called HPAI A(H5N1), for "highly pathogenic avian influenza virus of type A of subtype H5N1") causes H5N1 flu, commonly known as "avian influenza" or simply "bird flu", and is endemic in many bird populations, especially in Southeast Asia. This Asian lineage strain of HPAI A(H5N1) is spreading globally. It is epizootic (an epidemic in non-humans) and panzootic (a disease affecting animals of many species, especially over a wide area) killing tens of millions of birds and spurring the culling of hundreds of millions of other birds in an attempt to control its spread. Most references in the media to "bird flu" and most references to H5N1 are about this specific strain.[49][50]

At present, HPAI A(H5N1) is an avian disease and there is no evidence suggesting efficient human-to-human transmission of HPAI A(H5N1). In almost all cases, those infected have had extensive physical contact with infected birds.[51] In the future, H5N1 may mutate or reassort into a strain capable of efficient human-to-human transmission. Due to its high lethality and virulence, its endemic presence, and its large and increasing biological host reservoir, the H5N1 virus is the world's pandemic threat in the 2006–7 flu season, and billions of dollars are being raised and spent researching H5N1 and preparing for a potential influenza pandemic.[52]

Economic impact

Influenza produces direct costs due to lost productivity and associated medical treatment, as well as indirect costs of preventative measures. In the United States, influenza is responsible for a total cost of over $10 billion per year, while it has been estimated that a future pandemic could cause hundreds of billions of dollars in direct and indirect costs.[53] However, the economic impact of past pandemics have not been intensively studied, and some authors have suggested that the Spanish influenza actually had a positive long-term effect on per-capita income growth, despite a large reduction in the working population and severe short-term depressive effects.[54] Other studies have attempted to predict the costs of a pandemic as serious as the 1918 Spanish flu on the U.S. economy, where 30% of all workers became ill, and 2.5% were killed. A 30% sickness rate and a three-week length of illness would decrease gross domestic product by 5%. Additional costs would come from medical treatment of 18 million to 45 million people, and total economic costs would be approximately $700 billion.[55]

Preventative costs are also high. Governments worldwide have spent billions of U.S. dollars preparing and planning for a potential H5N1 avian influenza pandemic, with costs associated with purchasing drugs and vaccines as well as developing disaster drills and strategies for improved border controls.[52] On November 1 2005, President George W. Bush unveiled the National Strategy to Safeguard Against the Danger of Pandemic Influenza[56] backed by a request to Congress for $7.1 billion to begin implementing the plan.[57] Internationally, on January 18 2006 donor nations pledged US$2 billion to combat bird flu at the two-day International Pledging Conference on Avian and Human Influenza held in China.[58]

Up to 2006, over ten billion dollars have been spent and over two hundred million birds have been killed to try to contain H5N1 avian influenza.[59] However, as these efforts have been largely ineffective at controlling the spread of the virus, other approaches are being tried: for example, the Vietnamese government in 2005 adopted a combination of mass poultry vaccination, disinfecting, culling, information campaigns and bans on live poultry in cities.[60] As a result of such measures, the cost of poultry farming has increased, while the cost to consumers has gone down due to demand for poultry falling below supply. This has resulted in devastating losses for many farmers. Poor poultry farmers cannot afford mandated measures which keep their bird livestock from contact with wild birds (and other measures), thus risking losing their livelihood altogether. Multinational poultry farming is increasingly becoming unprofitable as H5N1 avian influenza becomes endemic in wild birds worldwide.[61] Financial ruin for poor poultry farmers, which can be as severe as threatening starvation, has caused some to commit suicide and many others to stop cooperating with efforts to deal with this virus – further increasing the human toll, the spread of the disease, and the chances of a pandemic mutation.[62][63]

See also

Information concerning flu research can be found at

References and notes

  1. 1.0 1.1
  2. Centers for Disease Control and Prevention. Lab Diagnosis of Influenza. Accessed on January 1, 2007
  3. 4.0 4.1 WHO Confirmed Human Cases of H5N1 Data published by WHO Epidemic and Pandemic Alert and Response (EPR). Accessed 24 Oct. 2006
  4. 5.0 5.1 Recommended composition of influenza virus vaccines for use in the 2006–2007 influenza season WHO report 2006-02-14. Accessed 19 October 2006.
  5. Weather and the Flu Season NPR Day to Day, December 17 2003. Accessed, 19 October 2006
  6. Shek LP, Lee BW. "Epidemiology and seasonality of respiratory tract virus infections in the tropics." Paediatr Respir Rev. 2003 Jun;4(2):105–11. PMID 12758047
  7. Dushoff J, Plotkin JB, Levin SA, Earn DJ. "Dynamical resonance can account for seasonality of influenza epidemics." Proc Natl Acad Sci U S A. 30 November2004;101(48):16915–6. PMID 15557003
  8. Cannell, J (2006). "Epidemic influenza and vitamin D". Epidemiol Infect. 134 (6): 1129–40. PMID 16959053. Unknown parameter |coauthors= ignored (help)
  9. HOPE-SIMPSON, R. "The nature of herpes zoster: a long-term study and a new hypothesis". Proc R Soc Med. 58: 9–20. PMID 14267505.
  10. Linday, L (2004). "Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites". Ann Otol Rhinol Laryngol. 113 (11): 891–901. PMID 15562899. Unknown parameter |coauthors= ignored (help)
  11. Influenza WHO Fact sheet N°211 revised March 2003. Accessed 22 October 2006
  12. Thompson, W (2003). "Mortality associated with influenza and respiratory syncytial virus in the United States". JAMA. 289 (2): 179–86. PMID 12517228. Unknown parameter |coauthors= ignored (help)
  13. Thompson, W (2004). "Influenza-associated hospitalizations in the United States". JAMA. 292 (11): 1333–40. PMID 15367555. Unknown parameter |coauthors= ignored (help)
  14. Flu factsheet National Institute of Allergy and Infectious Diseases Accessed 22 Dec 2006
  15. "Long intervals of stasis punctuated by bursts of positive selection in the seasonal evolution of influenza A virus". Biol Direct. 1 (1): 34. 2006. PMID 17067369.
  16. Parrish, C. "The origins of new pandemic viruses: the acquisition of new host ranges by canine parvovirus and influenza A viruses". Annual Rev Microbiol. 59: 553–86. PMID 16153179. Unknown parameter |coauthors= ignored (help)
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Further reading

Template:Col-1-of-2General
  • NEJM's Avian Influenza
  • Bernd Sebastian Kamps, Christian Hoffmann and Wolfgang Preiser (Eds.) Influenza Report 2006 Flying publisher 2006.
  • Arnold J. Levine 'Viruses' Scientific American Library, WH Freeman, 1992 ISBN 0-7167-5031-7
  • Samuel Baron et al. 'Medical Microbiology' Fourth Edition, The University of Texas Medical Branch at Galveston 1996 ISBN 0-9631172-1-1.
  • Cox NJ, Subbarao K. 'Influenza.' Lancet. 1999 Oct 9;354(9186):1277–82. PMID 10520648
History
  • Edwin D. Kilbourne Influenza Pandemics of the 20th Century Emerging Infectious Diseases Special Issue: Influenza Vol. 12, No. 1 January 2006
  • Richard Collier 'The Plague of the Spanish Lady' Macmillan publishers (London) 1974 ISBN 0-7490-0246-8
  • John M. Barry 'The Great Influenza: the Epic Story of the Deadliest Plague in History' Penguin 2004 ISBN 0-670-89473-7
Microbiology
  • Webster RG, Bean WJ, Gorman OT, Chambers TM, Kawaoka Y. "Evolution and ecology of influenza A viruses." Microbiol Rev. 1992 Mar;56(1):152–79. PMID 1579108
  • Scholtissek C. 'Molecular epidemiology of influenza.' Arch Virol Suppl. 1997;13:99–103. PMID 9413530
Template:Col-2-of-2Pathogenesis
  • Adolfo García-Sastre Antiviral Response in Pandemic Influenza Viruses 'Emerging Infectious Diseases Special Issue: Influenza Vol. 12, No. 1 January 2006
  • Zambon MC. 'The pathogenesis of influenza in humans.' Rev Med Virol. 2001 Jul–Aug;11(4):227–41. PMID 11479929
EpidemiologyTreatment and preventionResearch

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