Influenza is an enveloped virus of the family orthomyxovirus. They have a (-)stranded segmented RNA genome. It has two proteins on its surface which are particularly important, hemagglutinin(HA) and neuraminidase(NA). NA serves to cleave mucus, making it less viscous, and allowing the virus to move to infect the host. HA causes the virus particle to bind to cells, and facilitates endocytosis. Once the virus has been endocytosed, the pH of the endocytic vesicle drops, causing the virus to fuse with the membrane and release its genome into the cytoplasm.

Typically influenza undergoes a tremendous amount of genetic drift, with common strains changing from year to year, requiring a change in the vaccine. Strains are typically named after the type of HA and NA surface proteins they have, so a typical name would be something like "influenza H2N7". The normal reservoirs of the virus are pigs and fowl (chickens, ducks). Several years ago, over a million chickens were destroyed in Hong Kong because they were harboring a particularly virulent influenza strain that probably would have crossed over into humans eventually.

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

. 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:

And the map of an epidemic spreading can be viewed on

Works Cited

1. "Microbiology, and Introduction 7th edition", Tortora, Funke, Case, Copyright 2001 by Benjamion Cummings,
an imprint of Addison Wesly Logman, Inc.

2. © WHO/OMS, 1998 , last updated
Last updated Friday, 24 April 1998 .

3. © 1999 PBS/WGBH. This Web site was produced for PBS Online by WGBH.

I wrote this a couple weeks ago, right before spring break. Sent it to both local papers. They didn't publish it. Oh, well.

Influenza is here again. I did not recognize this year's form immediately. For two weeks I saw people with a headache right between their eyebrows, fever, muscle aches and cough. They had very little nasal drainage, sore throat or ear pain. They were all very tired. This was clearly viral and going around. Then I saw a single mother with three children. All four were sick, one really quite sick and one with laboratory confirmed influenza. Three out of the four had the headache. Ah-ha!

Influenza is not the stomach flu. This year's stomach flu is norovirus. It goes around every winter. Nausea, diarrhea, maybe vomiting. Try to keep up on fluids. Antibiotics don't work because they only kill bacteria, not viruses.

Influenza is an unusual virus. My information website says that in any one year, as many as 20 percent to the people in the world will get influenza. That is a LOT of people. Influenza is airborne and very contagious. We started asking for all people in the waiting room to wear masks as soon as we realized we have a big outbreak of influenza.

As a doctor I really did not understand influenza very well until my sixth year of practice. My daughter got it on November 30th. I saw 6 very sick people in a row in clinic. I had a person in the intensive care unit with influenza and bacterial pneumonia. I had had my influenza vaccine but that year the vaccine protected only 3 people out of 4. I was the 4th and got sick December first.

I put my daughter on antiviral medicine, but being an invincible doctor, I did not put myself on it. This was a mistake. I got very very sick. Influenza is different from asthma and pneumonia. In asthma, smooth muscle in the lungs narrow the airways. Inhalers relax the muscles. In pneumonia, there is fluid in the airways. Cough medicine helps and people need antibiotics if it is bacterial. Influenza makes the lung tissue swell, so the air spaces are partly swollen shut. Cough medicine doesn't help much. Antibiotics don't work. Inhalers don't work.

What works is rest. Rest, fluids, tylenol or ibuprofen for the muscle aches. All that stuff our mothers said.

When I got influenza my lungs were very swollen. There was less air space. I tried to go back to work after a week because my fever was down and doctors are invincible, right? By noon I was exhausted. I felt like I had run for miles. I put a pulse oximeter on my finger. My oxygen level was fine but my heartrate was 125. Normal is 60-100. My normal is 60-80. My heart was working extra hard to make up for the damage in my lungs. I had to go home. It took two months to heal enough to go back to work. During that two months my heartrate at rest was 100 and going up the stairs 125. I had to rest halfway up one flight of stairs. I realized that perhaps I am not invincible.

Influenza is contagious for 3-5 days in adults and up to 7 days for children. During that time you should stay home. Try not to expose people. When should you go back to school or work? Your heartrate is the key. Count the number of beats in a minute at rest. 60-100 is normal. Walk around. If your heartrate is over 100-110, I do not think you are ready to go back to work. If you become exhausted, you ae more likely to get bacterial pneumonia on top of the influenza.

And please think about getting a flu shot. It takes up to two weeks to fully protect you. This year mine seems to be working so far.

PS. Have some alcohol on hand. I think that flu freaks out the adrenalin system too, so a small amount of alcohol calms the heartrate down. Getting drunk, however, stresses the immune system more. I said small amount.

The human influenza virus (known colloquially as ‘the flu’) is responsible for many hundreds of thousands of deaths worldwide each year. The virus is relatively easy to transmit from person to person and even from animal to person in some cases of zoonotic strains. Indeed, the virus is so successful at spreading that it has previously caused global infections of one strain or multiple similar strains; most notably, the 1918-19 outbreak of H1N1 influenza, and a more recent outbreak of a similar strain.

On the influenza virus and humans
Human influenza appears in three different types – simply enough, named types A, B and C. Types A and B are the strains most often found in humans, and are usually the cause of the seasonal outbreaks of influenza in human society. Influenza B is rarely found in any species besides humans, however, it is influenza A which has been responsible for the pandemics mentioned above.
Influenza A is often zoonotic in nature; that is, it can be readily spread between humans and non-human animals. Notably, strains which have previously infected humans have been found to have originated from birds and from swine. Indeed, some birds have been found to be natural reservoirs for particular serotypes (subspecies) of the virus.

Influenza is easily transmitted from human to human. As it is a respiratory disease, it can be transmitted via respiratory droplets (from coughing or sneezing), but it can alo be spread via direct physical contact and indirectly, such as from unwashed hands and contaminated objects.

Mutation in influenza viruses
Rather than DNA, the influenza virus’ genome is composed of RNA, a single-stranded sequence of nucleotides. RNA has a much higher potential to mutate than DNA has, as unlike DNA polymerase (II), RNA polymerase does not ‘proof-read’ the synthesized strand. Any mutations in the ribonucleotide sequence, such as deletions or substitutions, are thus conserved. As the nature of an influenza infection is to proliferate rapidly in a host, the potential to produce altered strains rapidly is enormous.

Previous pandemics
By the World Health Organisation’s definition, an influenza outbreak is considered a pandemic when there are “community level outbreaks in at least one other country in a different WHO region” in addition to previously demonstrated human-to-human transmission of the novel strain in question. Such outbreaks have occurred in recent history; two particularly significant ones will be mentioned here.

In 1918, shortly after the end of the first World War, a new strain of the influenza A virus, serotype H1N1 appeared. The disease was colloquially dubbed ‘Spanish ‘flu’, though it is unlikely that the disease first emerged in Spain. Due to the nature of the influenza virus and conflicting historical reports, it is difficult to determine exactly from where the virus originated, but recent research places the first cases in the state of Kansas in the United States of America. The death toll is similarly difficult to determine, but conservative estimates place the figure at around 21 million mortalities. Considering the substantially smaller global population at the time, the disease was particularly deadly. The virus disappeared abruptly after its second wave. The cause of this is theorized to be improved treatment; however this is purely speculation.

A modern comparison to the 1918-19 pandemic is the more recent ‘swine flu’ pandemic. The virus which caused global panic in 2009 is closely related to the 1918-19 virus, being of the same H1N1 serotype. The virus spread globally swiftly, and on the 11th of June, 2009, the World Health Organisation officially declared the virus to have reached pandemic proportions. However, the virus had relatively low mortality compared to that of the 1918-19 strain, and was declared over in August of 2010 with around 18,500 confirmed mortalities.

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In`flu*en"za (?), n. [It. influenza influence, an epidemic formerly attributed by astrologers to the influence of the heavenly bodies, influenza. See Influence.] Med.

An epidemic affection characterized by acute nasal catarrh, or by inflammation of the throat or the bronchi, and usually accompanied by fever.


© Webster 1913.

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