Avian flu

Avian flu (also "bird flu", "avian influenza", "bird influenza"), means "flu from viruses adapted to birds", but is sometimes mistakenly used to refer to both other flu subsets and the viruses that cause them. (Example: from any flu virus rather than ones adapted to birds, e.g. Dog flu, Horse flu, Human flu, Swine flu), or (also incorrectly) even the virus itself. "Avian influenza strains are those well adapted to birds"EUROPEAN CENTRE FOR DISEASE PREVENTION AND CONTROL. Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner from excellent free on-line Book called Influenza Report 2006 which is a medical textbook that provides a comprehensive overview of epidemic and pandemic influenza. 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. Full HTML text of 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 The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005) Full text of online book by INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES Here is the tree showing evolution by antigenic drift since 2002 that created dozens of highly pathogenic varieties of the Z genotype of avian flu virus H5N1, some of which are increasingly adapted to mammals. Evolutionary characterization of the six internal genes of H5N1 human influenza A virus

All known avian flu viruses belong to the species of virus called 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").

As of 2006, "avian flu" is being commonly used to refer to infection from a particular subtype of Influenza A virus, H5N1, which is currently the world's major flu pandemic threat.

Avian flu 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 we know 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, we 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, this was basically the whole story of avian flu so far as anyone knew or cared (outside of the poultry industry). Now with H5N1, we have a whole new ballgame with H5N1 inventing new rules as it goes with behaviors never noticed before, and possibly never having occurred before. This is evolution right before our eyes. Even the Spanish flu virus did not behave like this. What is worth mentioning about illness from avian flu viruses is covered in H5N1 flu, Flu, and the subtype articles (H5N1, HxNy) linked below (and the references in those articles).

A few examples of correct and incorrect usage of the term "avian flu" itself follow. For more scientific information about avian flu, see the subtype links towards the bottom of this article, H5N1 flu, Flu, Influenzavirus A, and other linked articles.

Illustrative examples of correct usage

In technical contexts, correct usage of terms is necessary because precise distinctions are the essence of the communication.

"Avian influenza strains are those well adapted to birds"
"An outbreak of influenza A (H5N1), also known as 'avian flu' or 'bird flu,' has been reported in several countries throughout Asia." OSHA
"Avian influenza virus usually refers to influenza A viruses found chiefly in birds, but infections can occur in humans." CDC Avian Influenza (Bird Flu)
"Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of cases of severe disease and death in humans. Unlike normal seasonal influenza, where infection causes only mild respiratory symptoms in most people, the disease caused by H5N1 follows an unusually aggressive clinical course, with rapid deterioration and high fatality." Seasonal influenza is human flu. WHO Avian influenza frequently asked questions
"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." Greninger Paper (PDF)
Sometimes a virus contains both avian adapted genes and human adapted genes. Both the H2N2 and H3N2 pandemic strains contained avian flu virus RNA segments. "While the pandemic human influenza viruses of 1957 (H2N2) and 1968 (H3N2) clearly arose through reassortment between human and avian viruses, the influenza virus causing the 'Spanish flu' in 1918 appears to be entirely derived from an avian source (Belshe 2005)."

Illustrative examples of imprecise usage

In nontechnical contexts, imprecise usage of terms is typical when discussing complex things.

"A 1,000 square mile quarantine zone to combat an outbreak of bird flu was lifted in Scotland today - despite the spread of a similar disease south of the border." Here "bird flu" is used to mean "Asian lineage HPAI A(H5N1) flu" (which is a bird flu) and contrasted with flu from an avian adapted strain of H7N3 (which is also a bird flu). (Click the links for details.) News Avian flu quarantine zone lifted published May 1, 2006.

Sources and notes

Influenza | H5N1

Gourt Home::Gourt :: Avian flu

Illustrative examples of correct usage

Illustrative examples of imprecise usage

See also

Sources and notes