We know that a very large proportion of bacteria are essential to our good health. Every other day we see press release about the microbiome, and its multitude of health implications. Is there something equivalent with viruses. Do we have a stealthy microvirome that is essential to our health?

We know a few things about viruses:

  1. Typically, the more successful ones are more contagious but also less lethal. A virus that is more lethal and kills its human host more readily essentially commits suicide by depleting its resources quickly (human host).

  2. Viruses kill a lot of bacteria.

  3. Viruses fight each other off, crowd each other out.

From the above, we can advance an hypothesis of what a smart virus would do:

a) It would be highly contagious, but be rather benign;

b) It would kill "bad" bacteria and not "good" ones;

c) It would crowd out all other viruses to colonize the human host most successfully.

In other words, this smart virus would attempt to keep its human host as healthy as possible and keeping it free from all other bacterial and viral infections and diseases. Meanwhile, it would attempt to keep its human host as healthy and vibrant as possible. So, this human would remain mobile, interact closely with others, so the virus could propagate itself as successfully as possible.

I intuit they are many examples of such smart viruses. The common cold and the flu both come to mind. The common cold being the smarter of the two for obvious reasons (flu certainly reduces your energy and mobility a lot more relative to the common cold).

If the above has a grain of coherence, it would suggest that some benign viral infections and diseases such as the common cold may be actually good for us, as they actually protect us from a bunch of far worse bacterial and viral infections and diseases.

Similarly, do we have zillions of viruses within our bodies that are actually very good for us? They would not need to cause a disease at all, they would live in perfect harmony with their human host. Maybe they would be essential to a human host survival. In essence, do we have a bunch of good viruses within our system just as we have a bunch of good bacteria?


After being educated on the issue by a virologist (Georges Natsoulis), I understand the question needs answers at two completely different levels. First, our very own human genome has been in good part developed in conjunction with the input of left over viruses. Thus, without the input from viruses we would not be who we are. Second, viruses within our bodies do have their own virome (counterpart to the bacteria microbiome). And, the virome does influence our health and survival in a multitude of ways.

Back to the first answer that viruses make up a good part of our human genome, among the more frequent gene in our genome is reverse transcriptase, the key gene in retroviruses (e. g. HIV and relatives). Some scientists estimate that we have about 20,000 functional genes and up to 10,000 copies of reverse transcriptase. So, the latter (virus derived genes) would represent around half of the former (our own genes).

Many of our genes are in fact coopted versions of viral genes. Thus, viruses are an essential ingredient of our very own genome. And, these virus-related genes are very stable, passed on from one generation to the next just like any other genes. They do change slowly over time due to natural selection factors in a similar way as other genes.

Now, back to the second answer about the virome, the study reference disclosed by Chris Rogers (American Society for Microbiology, 2015) within the comment section under my question indicates that some viruses are explicitly beneficial. For instance some types of herpes viruses protect against various cancers. The virome, just like the microbiome are pretty lively and dynamic and can change quite a bit over the life of an individual depending on lifestyle, recent infections, etc.

Just like bacteria, nature is probably in a chronic state of fragile disequilibrium/equilibrium. A bacteria located within a certain organ can be very "good." While the very same bacteria located elsewhere in the body may be very "bad." Viruses may follow a fairly similar pattern.

When we suffer from a viral disease, we are only aware of the negative effect of a given virus without always fully understanding its implications (including good ones).


American Society for Microbiology. (2015). Viruses: You've heard the bad; here's the good. ScienceDaily. https://www.sciencedaily.com/releases/2015/04/150430170750.htm

  • Do you have a reputable citations for the fact that "a good portion of our very own genome is composed of left over viruses." and the links to reverse transcriptase and HIV along with the benefits reverse transcriptase provides us? – Chris Rogers Mar 15 at 6:10
  • I don't. I learned that from a professional virologist (Georges Natsoulis). I understand this is a well know fact within the field of virology. I As time permit, I may look up for a reference. – Sympa Mar 15 at 15:40

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