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| {{flu}} {{Influenza}} | | __NOTOC__ |
| '''For patient information click [[{{PAGENAME}} (patient information)|here]]''' | | {{Avian influenza}} |
| | '''For patient information, click [[{{PAGENAME}} (patient information)|here]]''' |
| | <br>'''For more information about seasonal human influenza virus that is not associated with animal exposure, see [[Influenza]]'''<br><br> |
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| {{CMG}} | | {{CMG}} |
| ==Overview==
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| ''For the H5N1 subtype of Avian influenza see [[H5N1]].''
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| Avian influenza, commonly known as ''Bird flu'', is a strain of the influenza virus which infects birds. Most bird flu viruses can only infect other birds. However, bird flu can pose health risks to people. The first case of a bird flu virus infecting a person directly was in Hong Kong in 1997. Since then, the bird flu virus has spread to birds in countries in Asia, Africa and Europe.
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| ==Background==
| | {{SK}} Bird flu; avian flu, Bird influenza, Avian influenza virus; Bird flu virus; Bird influenza virus; Zoonotic influenza; Variant influenza |
| '''Avian influenza''', sometimes '''Avian flu''', and commonly '''Bird flu''' refers to "[[influenza]] caused by [[virus]]es adapted to birds."<ref name=ECDPC> "Avian influenza strains are those well adapted to birds"[http://72.14.207.104/search?q=cache:72mkmIQKbIQJ:www.ecdc.eu.int/documents/AF050930/AF3_13_Actions_taked_in_connection_with_Avian_Flu.doc+%22Avian+influenza%22+%22adapted+to+birds%22&hl=en&gl=us&ct=clnk&cd=3 EUROPEAN CENTRE FOR DISEASE PREVENTION AND CONTROL]. </ref><ref name=influenzareport> [http://www.influenzareport.com/ir/ai.htm Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner] in ''Influenza Report 2006''</ref><ref>[http://www.nature.com/nature/journal/v437/n7062/full/nature04239.html Large-scale sequencing of human influenza reveals the dynamic nature of viral genome evolution] Nature magazine presents a summary of what has been discovered in the [[Influenza Genome Sequencing Project]].</ref><ref>[http://content.nejm.org/cgi/content/full/353/13/1374 Avian Influenza A (H5N1) Infection in Humans] by The Writing Committee of the [[World Health Organization]] (WHO) Consultation on Human Influenza A/H5 in the September 29, 2005 [[New England Journal of Medicine]]</ref><ref>[http://darwin.nap.edu/books/0309095042/html The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005)] Full text of online book by INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES</ref><ref>[http://www.cdc.gov/ncidod/EID/vol11no10/05-0644-G1.htm] CDC has a [[phylogenetic tree]] showing the relationship between dozens of highly [[pathogenic]] varieties of the Z genotype of avian flu virus H5N1 and ancestral strains.</ref><ref>[http://vir.sgmjournals.org/cgi/content/full/81/5/1293 Evolutionary characterization of the six internal genes of H5N1 human influenza A virus]</ref>
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| "Bird flu" is a phrase similar to "Swine flu", "Dog flu", "Horse flu", or "[[Human flu]]" in that it refers to an illness caused by any of many different strains of influenza viruses that have adapted to a specific host. All known viruses that cause influenza in birds belong to the species: ''[[Influenzavirus A|Influenza A virus]]''. All subtypes (but not all strains of all subtypes) of Influenza A virus are adapted to birds, which is why for many purposes avian flu virus ''is'' the Influenza A virus (note that the "A" does ''not'' stand for "avian").
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| Adaption is non-exclusive. Being adapted towards a particular species does not preclude adaptions, or partial adaptions, towards infecting different species. In this way strains of influenza viruses are adapted to multiple species, though may be preferential towards a particular host. For example, viruses responsible for [[influenza pandemics]] are adapted to both humans and birds. Recent [[influenza research]] into the genes of the [[Spanish Flu]] virus shows it to have genes adapted to both birds and humans; with more of its genes from birds than less deadly later pandemic strains.
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| ==Genetics== | | ==[[Avian influenza overview|Overview]]== |
| Genetic factors in distinguishing between "[[human flu]] viruses" and "avian flu viruses" include:
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| :'''PB2''': ([[RNA polymerase]]): [[Amino acid]] (or [[residue]]) position 627 in the PB2 protein encoded by the PB2 [[RNA]] gene. Until [[H5N1]], all known avian influenza viruses had a [[Glutamic acid|Glu]] at position 627, while all human influenza viruses had a [[lysine]].
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| :'''HA''': ([[hemagglutinin]]): Avian influenza HA bind alpha 2-3 [[sialic acid]] receptors while human influenza HA bind alpha 2-6 sialic acid receptors. Swine influenza viruses have the ability to bind both types of sialic acid receptors.
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| ==Influenza pandemic== | | ==[[Avian influenza historical perspective|Historical Perspective]]== |
| {{details more|Influenza pandemic}}
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| Pandemic flu viruses have some avian flu virus genes and usually some [[human flu]] virus genes. Both the [[H2N2]] and [[H3N2]] pandemic strains contained genes from avian influenza viruses. The new subtypes arose in pigs coinfected with avian and human viruses and were soon transferred to humans. Swine were considered the original "intermediate host" for influenza, because they supported reassortment of divergent subtypes. However, other hosts appear capable of similar coinfection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible.<ref name=Blanchard>Blanchard, Ben. "China says son likely infected father with bird flu." Reuters 10 Jen 2008 10 Jen 2008 <http://www.reuters.com/article/healthNews/idUSPEK27288320080110>.</ref> The Spanish flu virus strain may have been transmitted directly from birds to humans.<ref>[http://www.influenzareport.com/ir/ai.htm Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner]</ref>
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| In spite of their pandemic connection, avian influenza viruses are noninfectious for most species. When they are infectious they are usually asymptomatic, so the carrier does not have any disease from it. Thus while infected with an avian flu virus, the animal doesn't have a "[[flu]]". Typically, when illness (called "flu") from an avian flu virus ''does'' occur, it is the result of an avian flu virus strain adapted to one species spreading to another species (usually from one bird species to another bird species). So far as is known, the most common result of this is an illness so minor as to be not worth noticing (and thus little studied). But with the domestication of chickens and turkeys, humans have created species subtypes (domesticated poultry) that can catch an avian flu virus adapted to waterfowl and have it rapidly mutate into a form that kills in days over 90% of an entire flock and spread to other flocks and kill 90% of ''them'' and can only be stopped by killing every domestic bird in the area. Until [[H5N1]] infected humans in the 1990s, this was the only reason avian flu was considered important. Since then, avian flu viruses have been intensively studied; resulting in changes in what is believed about flu pandemics, changes in poultry farming, changes in flu vaccination research, and changes in flu pandemic planning.
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| [[H5N1]] has evolved into a flu virus strain that infects more species than any previously known flu virus strain, is deadlier than any previously known flu virus strain, and continues to evolve becoming both more widespread and more deadly causing [[Robert Webster]], a leading expert on avian flu, to publish an article titled "The world is teetering on the edge of a pandemic that could kill a large fraction of the human population" in ''[[American Scientist]]''. He called for adequate resources to fight what he sees as a major world threat to possibly billions of lives.<ref name=webster>
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| {{cite journal
| | ==[[Avian influenza classification|Classification]]== |
| | author=[[Robert Webster|Webster, R. G.]] and Walker, E. J. | title=The world is teetering on the edge of a pandemic that could kill a large fraction of the human population | journal=American Scientist | year=2003 | pages=122 | volume=91 | issue=2 |url=http://www.americanscientist.org/template/AssetDetail/assetid/17221?fulltext=true | id={{DOI|10.1511/2003.2.122}}
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| }} </ref> Since the article was written, the world community has spent billions of dollars fighting this threat with limited success.
| | ==[[Avian influenza pathophysiology|Pathophysiology]]== |
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| ==H5N1== | | ==[[Avian influenza causes|Causes]]== |
| {{H5N1}}
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| {{details more|H5N1|Transmission and infection of H5N1}}
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| The highly pathogenic Influenza A virus subtype [[H5N1]] virus is an emerging avian influenza virus that has been causing global concern as a potential [[pandemic]] threat. It is often referred to simply as "bird flu" or "avian influenza" even though it is only one subtype of avian influenza causing virus.
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| H5N1 has killed millions of poultry in a growing number of countries throughout Asia, Europe and Africa. Health experts are concerned that the co-existence of human flu viruses and avian flu viruses (especially H5N1) will provide an opportunity for genetic material to be exchanged between species-specific viruses, possibly creating a new virulent influenza strain that is easily transmissible and lethal to humans.<ref name=FSRIO>Food Safety Research Information Office. [http://fsrio.nal.usda.gov/document_fsheet.php?product_id=207 "A Focus on Avian Influenza"]. Created May 2006, Updated November 2007.</ref>
| | ==[[Avian influenza differential diagnosis|Differentiating Avian influenza from other Diseases]]== |
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| Since the first H5N1 outbreak occurred in 1997, there has been an increasing number of HPAI H5N1 bird-to-human transmissions leading to clinically severe and fatal human infections. However, because there is a significant species barrier that exists between birds and humans, the virus does not easily cross over to humans, though some cases of infection are being researched to discern whether human to human transmission is occurring.<ref name=Blanchard/> More research is necessary to understand the pathogenesis and epidemiology of the H5N1 virus in humans. Exposure routes and other disease transmission characteristics such as genetic and immunological factors, that may increase the likelihood of infection, are not clearly understood. <ref name=WHO>World Health Organization. (2006). [http://www.who.int/mediacentre/factsheets/avian_influenza/en/#humans Avian influenza (" bird flu") – The Disease in Humans.] Retrieved April 6, 2006.</ref>
| | ==[[Avian influenza epidemiology and demographics|Epidemiology and Demographics]]== |
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| Although millions of birds have become infected with the virus since its discovery, 206 humans have died from the H5N1 in twelve countries according to [[WHO]] data as of November 2007.
| | ==[[Avian influenza risk factors|Risk Factors]]== |
| (View the most current WHO Data regarding [http://www.who.int/csr/disease/avian_influenza/country/en/ Cumulative Number of Human Cases].)
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| The Avian Flu claimed at least 200 humans in Romania, Greece, Turkey and Russia. Epidemioloigists are afraid that the next time such a virus mutates, it could pass from human to human. If this form of transmission occurs, another big pandemic could result. However, disease-control centers around the world are making avian flu their top priority.
| | ==[[Avian influenza natural history, complications and prognosis|Natural History, Complications and Prognosis]]== |
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| ==Related Chapters== | | ==Diagnosis== |
| *[[H5N1]]
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| *[[Global spread of H5N1]]
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| *[[Transmission and infection of H5N1]]
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| *[[:Category:Subtypes of Influenza A virus|Subtypes of Influenza A virus]]
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| *[[Influenzavirus A]]
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| *[[Influenza pandemic]]
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| *[[Influenza Genome Sequencing Project]]
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| *[[Influenza research]]
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| *[[Influenza vaccine]]
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| *[[OIE/FAO Network of Expertise on Avian Influenza]]
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| *[[International Partnership on Avian and Pandemic Influenza]]
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| *[[Pandemic Preparedness and Response Act]]
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| ==References==
| | [[Avian influenza history and symptoms|History and Symptoms]] | [[Avian influenza physical examination|Physical Examination]] | [[Avian influenza laboratory findings|Laboratory Findings]] | [[Avian influenza chest x ray|Chest X Ray]] | [[Avian influenza other imaging findings|Other Imaging Findings]] | [[Avian influenza other diagnostic studies|Other Diagnostic Studies]] |
| {{reflist|2}}
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| ==External links== | | ==Treatment== |
| ;International
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| ;;World Health Organisation (WHO)
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| ;*[http://www.who.int/csr/disease/avian_influenza/en/ WHO Avian influenza resource (updated)]
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| ;*[http://www.who.int/csr/disease/avian_influenza/avianinfluenza_factsheetJan2006/en/index.html The United Nation's World Health Organization's Avian Flu Facts Sheet for 2006]
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| ;;Food and Agriculture Organization of the UN (FAO)
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| ;*[http://www.fao.org/ag/avian.html FAO Avian Influenza portal] Information resources, animations, videos, photos
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| ;*[http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/avian.html FAO Bird Flu disease card]
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| ;;World Organisation for Animal Health (OIE)
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| ;*[http://www.oie.int/downld/AVIAN%20INFLUENZA/A_AI-Asia.htm Official outbreak reports by country]
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| ;*[http://www.oie.int/eng/info/hebdo/a_isum.htm Official outbreak reports by week]
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| ;United States
| | [[Avian influenza medical therapy|Medical Therapy]] | [[Avian influenza primary prevention|Primary Prevention]] | [[Avian influenza secondary prevention|Secondary Prevention]] | [[Avian influenza cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Avian influenza future or investigational therapies|Future or Investigational Therapies]] |
| *[http://www.pandemicflu.gov PandemicFlu.Gov] U.S. Government avian and pandemic flu information
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| *[http://www.usaid.gov/our_work/global_health/home/News/news_items/avian_influenza.html US Avian Influenza Response] U.S. Agency for International Development (USAID)
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| ;Europe
| | ==Case Studies== |
| *[http://library.wur.nl/frontis/avian_influenza/ Avian Influenza: Prevention and Control] Proceedings of the Frontis workshop on Avian Influenza: Prevention and Control, Wageningen, The Netherlands
| | [[Avian influenza case study one|Case #1]] |
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| ;Other
| | ==Related Chapters== |
| *[http://www.fluwikie.com/ Flu Wiki] | | *[[H5N1]] |
| *[http://www.flupandemicalert.com Bird Flu Pandemic Alert and Breaking News] | | *Global Spread of H5N1 |
| *[http://declanbutler.info/blog/?p=58 The spread of avian flu with time; new maps exploiting Google Earth’s time series function] updated Google Earth maps of bird flu spread by [[Nature (journal)|Nature]] reporter Declan Butler | | *[[Transmission and infection of H5N1|Transmission and Infection of H5N1]] |
| *[http://www.birdfluthreat.org/essentials/main_info.php birdfluthreat.org information page] | | *[[:Category:Subtypes of Influenza A virus|Subtypes of Influenza A virus]] |
| | *[[Influenzavirus A|Influenza Virus A]] |
| | *[[Influenza pandemic|Influenza Pandemic]] |
| | *Influenza Genome Sequencing Project |
| | *[[Influenza vaccine|Influenza Vaccine]] |
| | *OIE/FAO Network of Expertise on Avian Influenza |
| | *International Partnership on Avian and Pandemic Influenza |
| | *[[Pandemic Preparedness and Response Act]] |
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| | ==External Links== |
| | *[http://www.who.int/csr/disease/avian_influenza/en/ WHO Avian influenza resource (updated)] |
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