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ALRIGHT, by popular demand, it is time for your local virologist to do a thread on “what is a virus”?

There is a lot of info (and mis-information) out there, so let’s take a step back and discuss the basics: WELCOME TO VIROLOGY 101.

Ready, set, go!

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We are all continuously exposed to all kinds of microbes. Most are harmless, but every now and then our body faces those that can cause disease (‘pathogen’). How? Many different ways! Here are just a few.

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There is a some confusion between different infectious agents – that’s OK! There are several types – including those made up of prokaryotic and eukaryotic cells – and those that are neither (such as viruses). These have been historically studied under micro and parasitology.

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A bit of history... A key observation in the discovery of viruses was when Dmitri noted that the infectious agent for a tobacco disease was small enough to pass through filters small enough to retain bacteria. Since then, viruses have been found in essentially all organisms.

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So, why was that observation important? Because that meant that viruses are small… REALLY small. So small we can’t directly visualize their structure with more conventional microscopes as we do for eukaryotic or bacterial cells.

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Now, let’s get it out of the way: viruses are not alive. They do not possess all the characteristics of a living organisms – so, no, you cannot ‘kill’ them. You can, however, inactivate them, denature them, neutralize them, etc.

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Here are the basic characteristics of a typical virus particle (also known as virion) and some of the key differences that made viruses to be quite different from living organisms.

Fun fact: my twitter handle relates to virus structure!

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Still confused? Imagine a virus as a genie in a lamp. The protein shell is the lamp, the carrier, protecting the genetic material that needs to be delivered inside a host cell in order for the virus to make more copies of itself.

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Viruses are obligate intracellular parasites. This means they can ONLY replicate inside a living host cell. Here are the general basic steps in the replication cycle for a typical virus and their dependence on components of the host cell.

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There is also a lot of confusion as to what viruses can and can’t do in terms of the species they can infect. Punchline: they show specificity. If this wasn’t the case, for example, all living organisms would be infected with exactly the same viruses.

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What makes a virus successful? Its ability to spread to new hosts. In many cases (but not always), the disease they cause facilitates their host-to-host transmission. For example, vomiting facilitates fecal-oral transmission of viruses that target the gastrointestinal tract.

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Same applies for respiratory viruses. Sneezing, coughing, etc facilitates their transmission through droplets. Here is how the size of those droplets impacts the transmission potential for a particular virus and why keeping our distance is so important.

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Where are all these viruses coming from? It depends. Here is the CDC definition of emerging infectious diseases and some examples of those transmitted from vertebrate animals (many of them) and those that aren’t.

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Viruses with an ARN genome (rather than DNA) are the main agents of emerging viral diseases, largely due to their high mutation rate (but, again, very few things in biology are exclusive!). Here is a comparison between different viruses, microorganisms, and even humans.

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Throwing this out here for those skeptical about vaccines and their use to prevent viral infections. I can do a future thread specifically on this topic if there is enough interest – just let me know!

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And, lastly: PLEASE listen to real scientists with the right credentials. Social media is facilitating the communication between scientists and non-scientists: take advantage of that. Many of us are here and would be more than happy to talk to you if you need us!