Flu Viruses - Why all the fuss?

Viruses are remarkably simple micro-organisms. They are made up of a core of genetic material protected by a protein coat, and have a unique characteristic: unlike any other organism, they need to be inside a living cell, called ‘host’, in order to be able to reproduce themselves. 

How do we become infected with the flu virus?

Flu viruses are no exception. They penetrate the cells that line the inside of our nose, mouth and trachea, and use our reproductive machinery to make new copies of themselves. That is when we become infected.

Do we need medications to fight off a flu virus infection?

Infection causes our body to produce antibodies to fight off the flu virus, and full recovery usually occurs in a relatively short time without complications. However, the flu virus may also induce our cells to produce proteins that attack our own defense mechanisms, making it more difficult for us to recover. Thus, we may need medications that block the virus’ ability to reproduce themselves to stop the infection. These are called antivirals. 

Is there only one type of flu virus?

There are three types of flu viruses: A, B, and C. Both seasonal and swine flu are caused by two different subtypes of type A influenza viruses, which, in turn, consist of a number of different strains. Vaccines and antiviral medications are effective when their composition matches the strain of flu virus they are intended for.

What does ‘mutation’ mean to us?

The problem is that flu viruses can mutate, that is, they can change into different viruses, over time. What this means to us, is that any vaccine and/or medication developed against a particular virus becomes useless as the virus mutates and turns into a different one. That is partly the reason why flu outbreaks are difficult to control, and why a new flu vaccine is developed every year.

What are antigenic drift and shift?

There are two ways in which a virus can mutate. One is by ‘antigenic drift.’ This occurs gradually and involves only minor changes in the virus’ structure. Viruses responsible for seasonal flu change continuously by antigenic drift.

The other one is by ‘antigenic shift.’ Antigenic shift occurs abruptly and involves major virus alterations due to a phenomenon called reassortment, whereby different flu strains infect the same host (usually an animal) and exchange their genetic material. Flu pandemics occur as a result of antigenic shift. The most important consequence is that the majority of people have no protection against the new virus, which is why flu pandemics can have a far more serious impact on humans than regular seasonal flu outbreaks.

Scientists at the Centers for Disease Prevention and Control warn that the swine flu virus may, at some point, become more deadly as a result of reassortment.

Does the flu virus spread easily among people?

Another problem with viruses is that they can rapidly spread from person to person. The seasonal flu virus, for example, causes hundreds of millions to fall ill worldwide, every winter. 

Mostly, the flu virus is passed among people through flu-contaminated air droplets expelled from the nose and mouth of infected individuals with cough and sneezes. These air droplets can float in the air for hours, sometimes traveling significant distances.  As we inhale them, the flu virus enters the upper airways and starts replicating, thereby initiating the infection process. The flu virus also spreads by direct contact. For example, when we shake hands with someone infected or contaminated, or we touch contaminated surfaces and objects and then we touch our mouth, nostrils, or eyes.

 

From Chapter 1

What is an influenza virus?

Viruses are micro-organisms capable of infecting both humans and plants, causing disease. They are considerably smaller than bacteria, some of which – unlike viruses – can live inside us without causing harm, helping our body perform at its best. Think, for example, of the so-called ... continued

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From Chapter 13

How do we become infected?

Viruses are known to be able to replicate themselves only by using the reproduction machinery of their host. So, they first need to enter inside their host’s cells. But how? In humans, the host cells of the influenza A virus are those lining the upper respiratory tract ... continued

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From Chapter 13

Swine flu is not new

The virus responsible for the deadly flu that is currently spreading around the world is a new form of H1N1, which is believed to have caused the Spanish flu pandemic of 1918. This is considered the worst disease outbreak in history and, yet, until recently, most people had never heard of it... continued

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From Chapter 15

Bird influenza A(H5N1)

Also known as avian flu, bird influenza A(H5N1) is considered becoming ‘progressively more pathogenic1’ by researchers and experts worldwide; certainly one of the deadliest threats to humanity. Currently endemic in wild birds and chickens, the virus responsible for bird flu is silently... continued

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