Avian influenza

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Influenza (flu)
H1N1 virus
Types
Vaccines
Treatment
Pandemics
Outbreaks
See also

Avian influenza is a disease of birds caused by a number of strains (or isolates) of serotypes (or subtypes) of the influenza A virus which are endemic in birds. Influenza A virus is the only species in the genus Influenzavirus A of the orthomyxoviridae family of viruses.[1][2][3][4][5][6][7][8]

Virus

"Bird flu" is one of many different types of influenza that are typically named after the preferred host organism for the virus, other similarly named influenzas are "Swine flu", "Dog flu", "Horse flu", and "Human flu". Avian influenza differs slightly as it is named after an entire vertebrate class with 8,800–10,200 species. All known viruses that cause avian influenza belong to the species of virus called Influenzavirus A [8]. Influenzavirus A are predominantly adapted to birds[citation needed], which is why for many purposes avian flu virus is the Influenza A virus[citation needed] (note that the "A" does not stand for "avian"). [9]

Adaptation is sometimes partial or multiple so a flu virus strain can be partially adapted to a species or adapted to more than one species [8]. Influenza pandemic viruses are human adapted and also bird adapted. Being adapted to one species does not mean another species can not catch it; nor does it mean it can not adapt to another species.

Wild aquatic birds are the natural hosts for a large variety of influenza A viruses. Occasionally viruses are transmitted from this reservoir to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics. Proteolytic activation of the hemagglutinin is an important determinant for pathogenicity and adaptation of the receptor binding specificity of the hemagglutinin and adaptation of the polymerase to new hosts play important roles in interspecies transmission.[8] [9]

These avian influenza viruses usually do not infect humans. However, cases have occurred in humans outside the United States. The disease can be transmitted to poultry workers or others who contact infected poultry or contaminated surfaces. Examples of workers at risk include the following:Poultry growers and their workers; Service technicians of poultry processing companies; Caretakers, layer barn workers, and chick workers at egg production facilities; and Workers involved in disease control and eradication (including Federal, contract, and company workers) [10]

Genetics

Genetic factors in distinguishing between Human Flu Viruses and Avian Flu Viruses include:

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 Glu at position 627, while all human influenza viruses had a lysine.
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.

Symptoms

In the first stage of the Avian Influenza, symptoms include fever, fatigue, coughing, sore throat, muscle aches and eye infections. Due to this, many people assume it is the Flu and thus do not seek medical treatment. However, if not treated the symptoms get worse and may result in paralysis and even death.

Terminology

Avian influenza is variously called bird flu, avian flu, or bird influenza. The correct term for the virus is Influenza A virus (species) or Influenzavirus A (genus). Individual serotypes (or subtypes) of the influenza A virus are named by a mnemonic, such as H5N1, which refers to the proteins that occur on the surface of the virus. The serotypes of influenza A that cause avian influenza are collectively called avian influenza viruses. The one serotype that has potential to cause pandemics in humans is H5N1, which is sometimes called avian influenza A (H5N1) virus.[11]

Influenza pandemic

Further information: Influenza pandemic

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. The Spanish flu virus strain may have been transmitted directly from birds to humans.[12]

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.

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.[13] Since the article was written, the world community has spent billions of dollars fighting this threat with limited success[citation needed].

H5N1

Further information: H5N1 and H5N1 flu

As of 2007, "avian flu" is being commonly used[citation needed] to refer to infection from a particular subtype of Influenza A virus, H5N1, which can cause severe illness in humans who are infected. This strain is transmitted through contact with infected birds, but has only been transmitted from one person to another in a few cases. H5N1 flu is therefore not at pandemic now and is not currently capable of causing a pandemic[citation needed]. Only if H5N1 mutates into a form that can be readily transmitted from one person to another could it cause a pandemic[citation needed].

On August 22, 2007, an Indonesian woman, 28, chicken trader was the 2nd person to die of bird flu on Bali, raising the death toll in the nation due to the disease to 84 (after 4 days of hospitalization). Tests in 2 local laboratories was positive for the H5N1 strain of the disease. 194 people — the majority of them in Indonesia died since 2003, according to the World Health Organization. [14]

The H5N1 virus is excreted in the droppings, saliva, and nasal secretions of infected birds. The virus is believed to enter humans through the mouth, nose, eyes, and lungs. Scientists believe that the virus has been transmitted to humans from contact with one of the following: Infected poultry that was sick or dead; Droppings of infected poultry; Contaminated litter; Contaminated surfaces such as egg collection containers. [15]

Although the human health risk of exposure to low pathogenic avian influenza viruses is not known, protective measures should be taken for anyone likely to have prolonged exposure to any avian influenza virus in an enclosed setting.

See also

Subtypes of Influenza A virus

Sources and notes

  1. ^ "Avian influenza strains are those well adapted to birds"EUROPEAN CENTRE FOR DISEASE PREVENTION AND CONTROL.
  2. ^ Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner in Influenza Report 2006
  3. ^ 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.
  4. ^ FAvian 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
  5. ^ The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005) Full text of online book by INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES
  6. ^ [1] 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.
  7. ^ Evolutionary characterization of the six internal genes of H5N1 human influenza A virus
  8. ^ a b c d Klenk; et al. (2008). "Avian Influenza: Molecular Mechanisms of Pathogenesis and Host Range". Animal Viruses: Molecular Biology. Caister Academic Press. ISBN 978-1-904455-22-6. {{cite book}}: Explicit use of et al. in: |author= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
  9. ^ a b Kawaoka Y (editor). (2006). Influenza Virology: Current Topics. Caister Academic Press. ISBN 978-1-904455-06-6 . {{cite book}}: |author= has generic name (help)
  10. ^ "National Institute for Occupational Safety and Health -Avian Influenza: Protecting Workers from Exposure". National Institute for Occupational Safety and Health. {{cite web}}: Unknown parameter |Accessdate= ignored (|accessdate= suggested) (help)
  11. ^ "Key Facts About Avian Influenza". Centers for Disease Control and Prevention. Retrieved 2007-09-19.
  12. ^ Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner
  13. ^ Webster, R. G. and Walker, E. J. (2003). "The world is teetering on the edge of a pandemic that could kill a large fraction of the human population". American Scientist. 91 (2): 122. doi:10.1511/2003.2.122.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ ITH, Bird flu kills Balinese woman, raises death toll to 84
  15. ^ "National Institute for Occupational Safety and Health -Avian Influenza: Protecting Workers from Exposure". National Institute for Occupational Safety and Health. {{cite web}}: Unknown parameter |Accessdate= ignored (|accessdate= suggested) (help)

External links

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