Science Questions

How do viruses cause disease?

Sun, 14th Dec 2008

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Bailey asked:

How do viruses cause disease?


Chris - Viruses are not actually living, they’re just an infectious bag of genes; in other words, they are some kind of coat that surrounds infectious material.  This can be DNA, which we’ve all heard of - Influenza Viruswe’ve all got that - or its genetic relative called RNA.

Viruses are also tiny: a flu virus is about 1/10,000'th of a millimetre across.  That’s too small for them to have any of the machinery they need to make new viruses inside themselves so they need to hijack a cell to do that.  There are viruses for plants, there are viruses for animals and there are even viruses for bacteria - bacteria can catch a cold too!

The flu virus has receptors, which are like viral Velcro, on the surface of the virus particle.  They will lock onto a target cell using these chemical receptors on the surface, which docks onto the cell surface.  They then go into the cell.  Once they’re in the cell they use it like a factory: they take it over and make it produce thousands or in some cases millions of copies of new viruses, which come streaming out of the cell.  They infect other cells to make more viruses, or they escape from the body and infect a new victim.

When they’re damaging cells - when they’re infecting cells - they can potentially kill them - that’s called lytic infection.  When they kill a cell that has a consequence for us because if it’s a cell in your airway, for example, it might damage the mucosa (the lining of your airway).  This means you get inflammation, a rather blocked-up, sniffy nose.  Plus, because you’ve got damage to the lining of the nose, you might get a bacterial infection on top so they can cause secondary infections.

Kat - Also something like Ebola. Ebola’s a virus where it just breaks down the tissues of the body.

Chris - Yes, it depends on the tropism.  It depends on what sort of cell the virus targets because if the virus goes  into the cells in your respiratory tract then it can damage the respiratory tract.  Flu can damage the lungs and this can cause respiratory failure.  Other viruses have a tropism towards other tissues.  For example, HIV has a tropism towards cells which have a CD4 chemical marker on them.

Kat - Those are immune cells.

Chris - Those are immune cells and so the virus goes into those cells. It can loiter in the cells for a long time before it actually does infect them but often it can damage the cells and make them dead.  If you lose those cells your immune system is disabled.  There’s a whole host of ways in which the viruses can damage different parts of the body.  When you’re got polio virus this comes out of your intestines, goes into your blood, goes to your spinal cord.  It then invades motor neurons which are the nerves which supply your muscles and the virus grows in the motor neurons, killing them in the process.  This paralyses you.  It depends what sort of cells the virus is targeted at to determine how likely it is to cause damage to that tissue and how likely it is to have consequences that are clinical.


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Try for a basic description. blakestyger, Sun, 11th May 2008

The ways in which viruses cause the symptoms of disease are as varied as the viruses

• Some viruses cause lysosomes to release their hydrolytic enzymes, which then
destroy the host cell.

• Some induce the host cell to synthesize toxins that cause a disease

• Some have toxic proteins in their envelope

The intensity of a viral infection is related to the host's ability to regenerate and
replace the damaged and infected cells as well as the host's immune system to be
able to detect the virus and destroy it.

I think,  lol smartbutdumb, Mon, 19th May 2008

Why just a link for Femle health and no offence guys but men get sick due to bugs, viruses just as much as women. Don't they? rosalind dna, Tue, 20th May 2008

The only reason it was that link is that it had the best simple explanation with some diagrams - there was no male equivalent.
The trouble with questions in this forum is that there is no way to tell what level the enquirer is working at unless it's made clear in the question. blakestyger, Fri, 23rd May 2008

I agree. It seems that some people here think I know things so I have to make it clear that I'm just a dumb ol' rodent    DoctorBeaver, Sun, 25th May 2008

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