Of Influenza Viruses and and strains

I found this information in the Centers for Disease Control and Prevention website and I think is really very informative. It provides information about the different strains of Influenza virus and their mechanism of infection and genetic modification. Youu may read on the article or visit the website directly. Very enlightening. :) Thanks!

Julius

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Types, Subtypes, and Strains

There are three types of influenza viruses: A, B, and C. Only influenza A viruses are further classified by subtype on the basis of the two main surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Influenza A subtypes and B viruses are further classified by strains.

Human Influenza Viruses and Avian Influenza A Viruses

Humans can be infected with influenza types A, B, and C viruses. Subtypes of influenza A that are currently circulating among people worldwide include H1N1, H1N2, and H3N2 viruses.

Wild birds are the natural host for all known subtypes of influenza A viruses. Typically, wild birds do not become sick when they are infected with avian influenza A viruses. However, domestic poultry, such as turkeys and chickens, can become very sick and die from avian influenza, and some avian influenza A viruses also can cause serious disease and death in wild birds.

Low Pathogenic versus Highly Pathogenic Avian Influenza A Viruses

Avian influenza A virus strains are further classified as low pathogenic (LPAI) or highly pathogenic (HPAI) on the basis of specific molecular genetic and pathogenesis criteria that require specific testing. Most avian influenza A viruses are LPAI viruses that are usually associated with mild disease in poultry. In contrast, HPAI viruses can cause severe illness and high mortality in poultry. More recently, some HPAI viruses (e.g., H5N1) have been found to cause no illness in some poultry, such as ducks. LPAI viruses have the potential to evolve into HPAI viruses and this has been documented in some poultry outbreaks. Avian influenza A viruses of the subtypes H5 and H7,including H5N1, H7N7, and H7N3 viruses, have been associated with HPAI, and human infection with these viruses have ranged from mild (H7N3, H7N7) to severe and fatal disease (H7N7, H5N1). Human illness due to infection with LPAI viruses has been documented, including very mild symptoms (e.g., conjunctivitis) to influenza-like illness. Examples of LPAI viruses that have infected humans include H7N7, H9N2, and H7N2.

In general, direct human infection with avian influenza viruses occurs very infrequently, and has been associated with direct contact (e.g., touching) infected sick or dead infected birds (domestic poultry).

How Influenza Viruses Change: Drift and Shift

Influenza viruses are dynamic and are continuously evolving. Influenza viruses can change in two different ways: antigenic drift and antigenic shift. Influenza viruses are changing by antigenic drift all the time, but antigenic shift happens only occasionally. Influenza type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift.

Antigenic drift refers to small, gradual changes that occur through point mutations in the two genes that contain the genetic material to produce the main surface proteins, hemagglutinin, and neuraminidase. These point mutations occur unpredictably and result in minor changes to these surface proteins. Antigenic drift produces new virus strains that may not be recognized by antibodies to earlier influenza strains. This process works as follows: a person infected with a particular influenza virus strain develops antibody against that strain. As newer virus strains appear, the antibodies against the older strains might not recognize the "newer" virus, and infection with a new strain can occur. This is one of the main reasons why people can become infected with influenza viruses more than one time and why global surveillance is critical in order to monitor the evolution of human influenza virus stains for selection of which strains should be included in the annual production of influenza vaccine. In most years, one or two of the three virus strains in the influenza vaccine are updated to keep up with the changes in the circulating influenza viruses. For this reason, people who want to be immunized against influenza need to be vaccinated every year.

Antigenic shift refers to an abrupt, major change to produce a novel influenza A virus subtype in humans that was not currently circulating among people (see more information below under Influenza Type A and Its Subtypes). Antigenic shift can occur either through direct animal (poultry)-to-human transmission or through mixing of human influenza A and animal influenza A virus genes to create a new human influenza A subtype virus through a process called genetic reassortment. Antigenic shift results in a new human influenza
A subtype. A global influenza pandemic (worldwide spread) may occur if three conditions are met:

A new subtype of influenza A virus is introduced into the human population.
The virus causes serious illness in humans.
The virus can spread easily from person to person in a sustained manner.

Types, Subtypes, and Strains

Influenza Type A and Its Subtypes

Influenza type A viruses can infect people, birds, pigs, horses, and other animals, but wild birds are the natural hosts for these viruses. Influenza type A viruses are divided into subtypes and named on the basis of two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). For example, an “H7N2 virus” designates an influenza A subtype that has an HA 7 protein and an NA 2 protein. Similarly an “H5N1” virus has an HA 5 protein and an NA 1 protein. There are 16 known HA subtypes and 9 known NA subtypes. Many different combinations of HA and NA proteins are possible. Only some influenza A subtypes (i.e., H1N1, H1N2, and H3N2) are currently in general circulation among people. Other subtypes are found most commonly in other animal species. For example, H7N7 and H3N8 viruses cause illness in horses, and H3N8 also has recently been shown to cause illness in dogs.

Only influenza A viruses infect birds, and all known subtypes of influenza A viruses can infect birds. However, there are substantial genetic differences between the influenza A subtypes that typically infect birds and those that infect both people and birds. Three prominent subtypes of the avian influenza A viruses that are known to infect both birds and people are:

Influenza A H5

Nine potential subtypes of H5 are known. H5 infections, such as HPAI H5N1 viruses currently circulating in Asia and Europe, have been documented among humans and sometimes cause severe illness or death.

Influenza A H7

Nine potential subtypes of H7 are known. H7 infection in humans is rare but can occur among persons who have direct contact with infected birds. Symptoms may include conjunctivitis and/or upper respiratory symptoms. H7 viruses have been associated with both LPAI (e.g., H7N2, H7N7) and HPAI (e.g., H7N3, H7N7), and have caused mild to severe and fatal illness in humans.

Influenza A H9

Nine potential subtypes of H9 are known; influenza A H9 has rarely been reported to infect humans. However, this subtype has been documented only in a low pathogenic form.

Influenza Type B

Influenza B viruses are usually found only in humans. Unlike influenza A viruses, these viruses are not classified according to subtype. Influenza B viruses can cause morbidity and mortality among humans, but in general are associated with less severe epidemics than influenza A viruses. Although influenza type B viruses can cause human epidemics, they have not caused pandemics.

Influenza Type C

Influenza type C viruses cause mild illness in humans and do not cause epidemics or pandemics. These viruses are not classified according to subtype.

Strains

Influenza B viruses and subtypes of influenza A virus are further characterized into strains. There are many different strains of influenza B viruses and of influenza A subtypes. New strains of influenza viruses appear and replace older strains. This process occurs through antigenic drift. When a new strain of human influenza virus emerges, antibody protection that may have developed after infection or vaccination with an older strain may not provide protection against the new strain. Therefore, the influenza vaccine is updated on a yearly basis to keep up with the changes in influenza viruses.

Information taken from Centers for Disease Control and Prevention
Visit their website at www.cdc.gov

Welcome Bio Students!

I am delighted to teach again! This coming weeks will be one of the busiest time for me since I need to take some "real" adjustments.

Also, I would like to take this opportunity to thank miss Gloria Bondoc-Abrazado for letting me handle her Genetics and Natural Science 2 (Biological Science) Class. Its great to be in the teaching field again. To my students, welcome!

I have been around in the blogger world for quite some time now and enjoying it! You may use this site for updates on our subject matter and read updates on what's hot in the world of biology.

Our blog will particularly provide additional readings in biology which you will find interesting. Many are updates regarding the recent bird flu outbreak and AIDS pandemic.

This will be a very huge adjustment for all of us but, with your cooperation and diligence, surely, we will be able to accomplish something worthwhile at the end of my teaching substitution career and you being students of Science as well.

Let's make the most out of our pagsasama! Cheers!


Julius

Word Power: Epidemic or Pandemic?

Hello Friends! I am introducing a new segment of our blog which is called WORD POWER!. Whenever you see such posts, it surely tackles about unique words or expressions which you frequently read in medical articles, books and journals.

Being able to understand these words empowers you to read on medical articles without difficulty and keeps you on a competitive edge with other people. So here it is!

Most people tend to interchange the meaning between pandemic and epidemic. These two words are widely used in the medical field, specifially, in the world of microbiology.

With the advent of bird flu virus threat and other related infections, knowing how to distinguish the meaning and the relative differences of the two words will provide you greater advantage and clear understanding on every articles where these words were used.

Entries in Merriam Webster give clear distinctioin between the two words.

Main Entry: 1ep·i·dem·ic

Etymology: French épidémique, from Middle French, from epidemie, n., epidemic, from Late Latin epidemia, from Greek epidEmia visit, epidemic, from epidEmos visiting, epidemic, from epi- + dEmos people -- more at DEMAGOGUE

1 : affecting or tending to affect a disproportionately large number of individuals within a population, community, or region at the same time

Main Entry: 1pan·dem·ic

Etymology: Late Latin pandemus, from Greek pandEmos of all the people, from pan- + dEmos people -- more at DEMAGOGUE

: occurring over a wide geographic area and affecting an exceptionally high proportion of the population

For more information, please click on the Post Title Link to lead you to the website source. Thank you.

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A rather more helpful explanation is available in the site below. It cited the difference between endemi, epidemic and pandemic.

Endemic: a disease that exists permanently in a particular region or population. Malaria is a constant worry in parts of Africa.

Epidemic: An outbreak of disease that attacks many peoples at about the same time and may spread through one or several communities.

Pandemic: When an epidemic spreads throughout the world.

http://www.mansfieldct.org/schools/mms/staff/hand/immnotes.htm

Dictionary.com provides similar explanation:

Pandemic ultimately derives from Greek pandemos, of all the people, from pan-, all + demos, people

Usage: Difference between endemic, epidemic, and pandemic:

Endemic is peculiar to a district or particular locality, or class of persons ("diseases endemic to the tropics"). That which is epidemic is common to, or affecting at the same time, a large number in a community ("an epidemic outbreak of influenza"). Pandemic is epidemic over a wide geographical area.

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See! We are learning! Its nice to know all these stuff for it frees you from reading difficulties! Information is power! :) Keep on reading!

Julius

Pig Flu Virus?

Aside from birds, pigs are one vital candidate in the transmisson of flu.

(Picture taken from CNN)

Hi Readers!

Researchers are eyeing on another source of flu virus that may pose greater threat to humans more than bird flu due to their more-than-close association with us.

Just recently, researchers are looking at the possibility of the spread of a pig flu virus. Pigs are more biologically similar in function and structure with humans than in birds. This fact provides more reason that a subtle pig flu outbreak may expedite a more deadly contamination with humans and may start a world-wide panick which most of us are totally unprepared.

Viruses differ in their ability to infect animals and plants and may well jump from one organism to another and possibly start a whole new strain. This "species jumping" is caused by the virus' ability to change genetically and add another host of animals in their infection list.

As stated in our previous post, viruses lacks the ability to repair specific genome damage during replication of their genetic material. This apparent biological infirmity confers the organism the ability to undergo dramatic change from one strain to another rendering most organisms unable to cope up with attcks due to lack of preformed defenses (antibodies) .

Likewise, dogs, seals, horses, and ferrets are more prone to these attacks and pose greater theat to the the survival of the human population.

Julius

Why do AIDS and Avian Influenza and other diseases caused by viruses difficult to treat?

This week protesters marched to US capitol demanding the reauthorization of Ryan White Care Act which aims to promote basic health care services for AIDS victims who lacks basic health care insurance to support medication and other needs to treat the disease.

It is reported that more than 1 million Americans are afflicted with the disease. More and more people are being infected every year and the numbers would continue to rise as people engage in risky behaviors which put them more susceptible to the disease.

Just how the development of AIDS vaccine so hard to device lies on the ever changing form of the virus. Through laboratory test, it was shown that more than one strain of virus is present in an AIDS patient.

This fact provides us with valuable clues to the nature of the AIDS virus and empower us to device treatment which is tailored to how the virus advance on an infected patient.

This works the same way with Avaian Influenza (H5N1) strain. The killer bird flu virus was believed to have already developed the ability to infect humans. Its mutation works in two ways: through antigenic drift and antigenic shift.

Antigenic drift is a small change to the genetic information contained in the virus due to the virus' lack of proofreading ability during genetic replication. Humans are equipped with this competency and allow us to maintain our genetic integrity and discourage unallowable changes.

This small changes creates an invariably small, unique changes to the genetic composition of the virus. This issue is important for it allows us to predict the strain of virus that will more likely to be prevalent in the coming flu season. It will also give local administrators to adjust the compositon of flu vaccines to be given in the coming season.

In contrast, anti-genetic shift works where a virus can interchange or "mate" its genetic composition with another virus species thereby producing a completely different type which in most cases are more virulent (extremely pathogenic or producing severe disease).

The latter definition is of major concern to scientists working on preventing the spread of avian influenza and eventually acquire the necessary mechanism to infect humans through the process enumerated above.

For your additional readings, please visit the following site below:

www.who.int/mediacentre/factsheets/avian_influenza/en/index.html
www.unaids.org/wad2004/EPIupdate2004_html_en/epi04_00_en.htm