THE FLU VIRUS -- INFLUENZA
Influenza is unique because it is one of the world's oldest and most deadly viruses. The first major epidemic is described by Hippocrates in 412 BC, and similar epidemic wiping out villages and cities are described every century ever since. Influenza occurs due to minor changes in the viral antigenic proteins - what is knows as antigenic drift. Which accounts for the changes of the virus from one season to the other.
The influenza virus is divided into two types --- Influenza A, which effects non-human animals, as well as people, and Influenza B - which predominantly spreads among humans. Like other viruses belonging to the genus Influenza virus, influenza consists of eight separate RNA segments enclosed by an inner protein layer. Influenza's lipid bi layer is embedded with two kinds of spikes, hemmagglutin (H) and neuraminidase(N). The virus recognizes and attaches the host using the H spikes. The hemmaglutin also allows the virus to be detected by the hemmaggltination inhibition test -- one of the most common tests to identify the Influenza virus. The N spikes allow the virus to separate from the host cell after intracellular reproduction
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The Influenza virus typically infects the mucous membranes of the respiratory system such as the throat, nasal cavity and lungs. The infection of the lungs is not common, but usually will result in viral pneumonia. The main symptoms of influenza are chills, body aches, fever, tiredness, and muscle weakness. A lot of the time, it is also identified by cold like symptoms of runny nose, coughing and throat ache. However, those symptoms are actually caused by secondary bacterial infection. Influanza weakens the body's immune system making the body susceptible to bacteria. Influenza is spread by droplet transmission - the virus spreads in a mucous droplet discharged in the air by sneezing, coughing, or even breathing. The Influenza virus is incredibly infectious because it can easily spread via mucous produced by the secondary bacteria infections. A flue epidemic can start within a few days of the first infection.
The best way to test for the Influenza virus is by doing the hemmagglutinin - inhibition tests to detect antibodies during acute infections. A faster diagnosis may be achieved by direct detection of the viral antigens in nasal secretion. Polymerase chain reaction and antigen-capture ELISA may also be used.
There is no sure way to prevent the Influenza virus. The flu vaccines that are given to the population every year are not a sure way since the vaccine only builds immunity to one or two antigens. The vaccine has to be updated every year, though in the recent years, doctors have been trying to predict the new flu strains by watching the epidemics that spread in Asia and Africa since usually those countinents are affected first. The best way to fight Influenza is prevention. That is, during the flu season , avoid people who may have symptoms, don't share food or drink and avoid crowded areas like malls around the holidays and movie theaters where people are in close contact for a prolonged period of time, which is ideal for the droplet transmission. Unfortunately, other Influenza breeding grounds are schools, offices and public transportation -- places that can't be avoided.
Currently there are several prescription drugs that will prevent the effects of Influenza and shorten the duration of the illness. They contain amatadineand rimatadine, which inhibit production of neuraminidase. Without neuraminidase the virus can't separate from the host cell and go on infecting other cells. This significantly decreases the viral count in the host. This chemical is the active ingredient in commercial prescription drugs such Relenza TM (inhaled) and Tamiflu TM (given orally).
The Influenza virus has been with us for many centuries, and has been responsible for millions of deaths, such as in the epidemic of 1918 when more then 20 million people world wide died from influence, or complications associated with influenza. However, the chance to find one, true vaccine for this is near to impossible because of the amazing speed with which this virus mutates. The best thing to do once infected is to avoid other people to prevent spreading the virus. Most of the time, symptoms pass after a few days, though it will leave the patient tired and worn out for almost a month. Influenza is responsible for most school absences, work leaves and infant illness. It has been part of our society for so long, through it is next to impossible to picture a winter without it.
You may view pictures of Influanza on:
http://www.uct.ac.za/depts/mmi/stannard/fluvirus.html.
And the map of an epidemic spreading can be viewed on
http://www.pbs.org/wgbh/amex/influenza/maps/index.html.
Works Cited
1. "Microbiology, and Introduction 7th edition", Tortora, Funke, Case, Copyright 2001 by Benjamion Cummings,
an imprint of Addison Wesly Logman, Inc.
2. http://www.who.int/emc/diseases/flu/ © WHO/OMS, 1998 , last updated
Last updated Friday, 24 April 1998 .
3. http://www.pbs.org/wgbh/amex/influenza/ © 1999 PBS/WGBH.
This Web site was produced for PBS Online by WGBH.