Health / Medicine / Microbiology / Science

Going viral

“Why can’t we treat viral and bacterial infections with the same medication?”

Although the symptoms of viral and bacterial infections can be similar, and they spread in similar ways, bacteria and viruses are very different. A bacterium is a living cell, albeit a simple one compared to a human cell. It shares features with a human cell, like a cell membrane and DNA, and they have similar needs for energy. A virus is even simpler. The scientist Peter Medawar described viruses as “a piece of bad news wrapped in a protein coat”. Outside of a living cell, they don’t grow, use energy or reproduce themselves, which are normally considered to be signs of a living organism. They just exist. They don’t even always use DNA, the double-stranded helix which carries genetic information. Some of them use RNA, which has only a single strand.

It’s when it gets into the right kind of living cell that a virus can really take off. It uses the host cell to make more and more copies of itself, churning them out to infect more and more other cells. By contrast, a bacterial cell can replicate itself.

When you’re infected with either a virus or a bacterium, the symptoms you experience are a result of the damage the infection is doing to your body, plus your body’s own response to try and kill the infection. For example, inflammation can cause pain and discomfort, but it’s a protective mechanism involved in responding to infection. The symptoms of viral and bacterial infections can be treated using the same medication. A stuffy nose is a stuffy nose, regardless of whether it’s caused by a bacterium or a virus, and that’s why a decongestant spray will work in both cases.

Better take your medicine, Mr Bear.

What about antibiotics, though? Although “anti” means “against” and “biotic” just means “associated with or derived from living organisms”, antibiotics don’t actually harm all living organisms. If they did, we wouldn’t be able to take them. Instead, they could more accurately be called “antibacterials”. They target bacteria, sometimes very specifically. That means that they have no way of interacting with a virus, which is hidden inside your body’s own cells. They’re also ineffective against other pathogens, like fungi (so antibiotic cream won’t do anything for your athlete’s foot).

This is where antivirals come in. These can attack viruses, but they do so in a different way, by inhibiting their development in various ways.

So when you have a sore throat and you go to the doctor, they probably won’t prescribe you antibiotics. For one thing, we need to hold back our antibiotics to fight against deadly diseases. For another, your sore throat could easily be caused by a virus, in which case the antibiotic will do nothing but upset your digestive system.

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6 thoughts on “Going viral

  1. So…when you say bacteria are simpler, does that mean that they don’t have organelles? Also, I didn’t know some viruses are DNA based! I thought they are all RNA.

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    • Yep! Bacteria store their DNA in a loop attached to the cell membrane, instead of in chromosomes, so they don’t even have a nucleus. Some biologists resist saying they’re simpler, since they are highly evolved for their environments, but I think it’s a good way of denoting the lack of membrane-bound organelles.

      At one point, I thought that was the definition of a virus, but apparently not. Smallpox is a DNA virus, for example. (So is hep B, sort of — it’s not classified as a DNA virus because it uses RNA to replicate, but its genome is DNA.)

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      • OK, so is it also true that cells without organelles are prokaryotes and those with are eukaryotes, thus making bacteria prokaryotes?

        Interesting about the DNA based viruses; seems to me that their existence might have implications for origin-of-life theories. I wonder if it’s possible to tell when they first came into existence? Do we even know that for viruses?

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      • Yep, bacteria are prokaryotes, and so are archaea. The other definition of prokaryotic cells people sometimes use is that they’re a single cell, but that’s not true — there are eukaryotic single cells, like the protists.

        I haven’t read anything specifically on DNA viruses and origin of life theories yet. I think it’s difficult since viruses paste themselves everywhere (especially DNA ones) and mess up phylogenies. I’ll have a dig into this one!

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      • Thanks! And if you don’t mind, what’s the defining difference between bacteria and archea?

        Yeah, my thoughts after that comment were that it is probably really difficult to trace the evolutionary history of viruses.

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      • It’s not a huge difference — they were thought to be the same until genetic sequencing was done. Archaea don’t have peptidoglycan in their cell membranes. They tend to be extremophiles.

        I know it’s been done for HIV and SIV, for example, so it is possible. But whether they can get that far back is another question.

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