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  • Writer's pictureRuth Hull

Understanding Viruses and Viral Infections: Your Body's Immune Response Explained


It’s winter time here in Perth and with all the rain and the cold winds viral infections seem to be flying around again so I thought I’d chat a bit about viruses.


Understanding viruses


What is a virus?

Viruses are fascinating 'things' - I'm not sure what else to call them! They are technically considered non-living because they contain no cells, cannot reproduce (unless in a host), do not breathe, do not excrete - they lack many of the characteristics that help biologists differentiate between what is living or non-living.


In fact, a virus is simply a tiny particle composed of DNA or RNA inside a protein shell. Nothing more.


Instead of thinking of a virus as a living creature out to destroy the world, think of it rather as a piece of machinery. A piece of machinery that can do nothing without a host (such as a human, animal or even a bacteria).


Viruses are small. I mean, really small!


So small that, according to Khan Academy, tens of millions of viruses can fit onto the head of a pin.


Viruses are also everywhere. There are more viruses on earth than any other pathogen, or even any other cellular organism. For example, "a liter of seawater collected in marine surface waters typically contains at least 10 billion microbes and 100 billion viruses—the vast majority of which remain unidentified and uncharacterized" (Weitz and Wilhelm, 2012).



"There may be a hundred million times more viruses on Earth than there are stars in the universe." Weitz and Wilhelm, 2012


There are more viruses on earth than any other pathogen, or even any other cellular organism.
There are more viruses on earth than any other pathogen, or even any other cellular organism.


Where do viruses come from?

There is no clear answer to this question but there are quite a few theories:


  • Some scientists suggest that viruses developed from genetic elements that gained the ability to move between cells.

  • Other scientists argue that viruses are the remnants of once free-living organisms.

  • Still other scientists think that perhaps viruses existed before cellular life, they pre-date us.

A good question to ask is: 'did we maybe evolve from viruses?' Or, if we didn't evolve from them, have they played any role in our evolution? Have they shaped us in some way?


Are they really our enemies?



Human Endogenous Retroviruses (HERVs)


To help you answer this question, think about this: approximately 8% of our human genome is composed of sequences with viral origin (Grandi and Tramontano, 2018). These sequences are called human Endogenous Retroviruses (HERVs) and are thought to be remnants of viruses that once infected our primate ancestors and that have now, over millenia, become part of us and our physiology. It is argued that this co-evolution between HERVs and humans has brought innovation and diversity to our genome and our physiology.

"While HERVs are products of ancestral exogenous viral infections pervading primates, they became major contributors in shaping and improving the human antiviral immunity." Grandi and Tramontano, 2018


Understanding viral infections



What happens when we get a viral infection?

Viral infections are very common and most young children get up to 12 viral infections a year in their first few years of life. The common cold, chickenpox, most ear infections - these are all viral infections and their role is to "exercise" our natural defence mechanisms and help us develop strong immune systems.


Once inside the body, viruses enter their target cells and use those cells to reproduce themselves. Luckily, our bodies have many different response mechanisms to viruses. Often, our first line of defence will be heat, swelling, pain and generally feeling yuk - in other words, fever and inflammation.


  • Fever - Have you ever wondered why you get so hot when sick? It is your body's normal response to toxins released by the microbes (be they bacteria, fungi or viruses) infecting you. This increase in temperature intensifies the effects of your body’s own antimicrobial substances, inhibits microbial growth and increases the speed of tissue repair.

  • Inflammation - Likewise, when tissues in your body swell up (for example, your throat gets red and sore during a throat infection), this inflammation is helping to prevent the spread of further tissue damage, to prepare the damaged tissue for repair and to help clear the area of microbes and toxins.

In addition to fever and inflammation, our body produces many different types of 'fighting cells' and chemicals to destroy foreign invaders. For example:


  • Cytotoxic T-cells patrol your system looking for cells infected by viruses. If they find any such cells, the cytotoxic T-cells release a substance that destroys these cells. The word cytotoxic actually means toxic to cells.

  • Similarly, natural killer cells (NK cells) also patrol for, and destroy, infected cells. I think the name says it all!

  • Virally infected cells also send out signals to our immune system that they are in trouble - these signals are tiny proteins called interferons.

  • And if that isn't enough, once in contact with a virus, our immune system produces antibodies. These are proteins which are able to recognise specific invading pathogens, bind to them and neutralise them.

So if you get a virus, remember that you have already had many and your body has coped with them.


What can we do when we have a viral infection?


Viral infections do not respond to antibiotics and often the best way to treat a mild viral infection is to rest, drink plenty of fluids, eat nutritious foods and let your immune system do its job. Most importantly, be aware that viral infections are often very contagious and so it is vital that you stay at home and away from other people until your symptoms have passed. If your infection is more severe, then please seek medical help.


Immune boosting foods that can help you fight your viral infection include:


  • garlic

  • raw honey

  • turmeric

  • and ginger.

If you enjoy reading about the human body and want to learn more, then subscribe to my blog and you'll get access to a special subscribers-only resource page. There you'll find a free chapter from my book Anatomy, Physiology and Pathology for Therapists and Healthcare Professionals. Enjoy!

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