Can we escape viruses?
November 1, 2020 10:43 PM   Subscribe

When we eventually develop spaceships that travel between the stars, will new viruses still plague the travelers?

Assume we'll quarantine the travelers before the journey and screen them to make sure they're all healthy. Also, they will never come back to Earth or have in-person contact with Earth people again.

Would they live the rest of their lives without ever getting another cold or flu? Or are viruses an inevitable side effect of being alive? And if so is there a minimum population they would need to perpetuate the occurrence of new viruses?

I don't have any motivation for asking this aside from curiosity.
posted by DrumsIntheDeep to Health & Fitness (11 answers total) 6 users marked this as a favorite
I work with lab animals and animal facilities strive really hard to keep the housed animals free from any kind of virus or bacteria, because that would introduce uncertainty and bias into the experiments. For example, if you do a study on the flu in lab mice and your animals have some kind of respiratory virus your results wont be reproducible by another lab, and likely not useful. They succeed in this by enforcing strict rules for how other animals are allowed to enter the facility. For example, the sections with the highest hygiene status only allow other animals to enter via embryo transfer. That means, you take out the embryo from your desired mouse strain, cryogenically freeze it, transport it to the facility and then reinsert it into your host mouse.
Also, animal keepers are not allowed to have any pets, access to the facility is through air locks, all food and water gets sterilized.
Meaning, you can keep pathogens out, but it's a lot of work, and beeing in a space ship without contact to other human populations will certainly work.
But the human microbiome contains many different species of benign bacteria that are beneficial to you and would be difficult to completely remove. And I guess as long as you have bacteria with you, sooner or later one of them will mutate and become a pathogen, especially in the absence of competition from other pathogens.
If you would use something like embryo transfer, or straight up print humans onboard your spaceship, I guess it would take a very long time for something like viruses if bacteria to reevolve. Also, the human body is a very nice bioreactor, so who knows.
posted by SweetLiesOfBokonon at 11:43 PM on November 1 [9 favorites]

If we put a group of people without viruses whatsoever on a spaceship, then viruses would not spontaneously appear out of nowhere.

A lot of viruses (and other diseases) that cause problems for humans infect multiple species; the challenge is that in many cases they don't cause serious illness in those other species; these are called reservoir hosts. This is (in part) why they are so hard to get rid of; even if you can immunize people against them, they can hang out in bats or pigs or whatever and come back to people eventually down the road.

The diseases mankind has done the best job of eliminating, such as polio and smallpox, only infect people, so we can actually immunize all the people and get rid of them. Take the flu as an example -- Influenza in particular has a number of strains that can infect dozens of species; apparently it's originally a seabird disease centuries ago. So to actually wipe out influenza, we'd need to immunize not only a large enough share of the human population, but also of the pig population, the chicken and duck populations, the various wild migrating birds that can spread it, and so on. Basically impossible.

All that said, people contain an awful lot of microorganisms and viruses mutate quickly; something that may be completely harmless to the point we've never studied it or even really noticed it before could evolve into something more virulent and problematic in the long run on this isolated spaceship. But it would likely a lot easier containing and dealing with it on a (massive, well-equipped) spaceship than in a more complex ecosystem.

So population size is relevant in this hypothetical case where a space virus evolves from something people carry. If a virus spontaneously mutates into something problematic, once everybody on the ship has had it and either died or developed an immune response to it, then the virus will have nowhere to go until there are new people without an immunity and will in all likelihood die out waiting for a new generation of victims to be born. (Viruses contain multitudes, of course -- some can survive a long time outside of the body, and some like HIV can infect people for a very long time -- so there exist theoretical ways for a virus to survive in this scenario.)

If you want a detailed understanding, David Quammen's Spillover is a great read on the history of zoonotic diseases, of bacteria and viruses. I finished it literally today, and couldn't recommend it more highly, assuming learning more about a variety of diseases spreading into humans is a thing you want to do in this year.
posted by Superilla at 11:47 PM on November 1 [3 favorites]

Some viruses can exist in a latent form or "phase" in the DNA in the cells of otherwise healthy people, who were once infected.

These viruses lie dormant, until they become active and enter lytic phase, where they use the cellular machinery to make copies of themselves. Pathogenic viruses trigger the immune system and raise symptoms that cause viral shedding. Contact between humans can then spread virus to those who are uninfected, be it on Earth or in space.

Some examples of these that cause disease when active include those in the Herpesviradae family: Herpes simplex (HSV), Epstein-Barr, human cytomegalovirus, and varicella, for instance. HIV is another example, which resides in CD4 cells.

It is also thought that common ancestors of viruses are also a part of our DNA in the form of transposable elements, which jump around our genome and can cause problems.

As far as typical viruses go, it may be very difficult to find a space traveler who has never been exposed to anything at any point in their pre-space stay on Earth. They are bound to have picked up (and kept) many viruses, while still being healthy. Most latent virus infections are currently incurable, because the viral genome has integrated itself into host cells where it cannot be removed.

Some very new therapies are looking at gene therapy in animal models to try to excise latent infections. However, most of the therapies you see for common herpes, as an example, treat symptoms of the virus in lytic phase, when it is causing visible symptoms.

In patients with HIV, as another example, retroviral therapies can slow and stop the infection of immune cells by the virus, but a pool of latent HIV always remains. Stopping retroviral drug treatment will ultimately allow the virus to reproduce again in ever larger numbers, giving rise to AIDS symptoms and diseases related to a compromised immune system, which is why patients must continue to take medication indefinitely, to manage the virus.
posted by They sucked his brains out! at 11:51 PM on November 1 [5 favorites]

Human endogenous retroviruses (HERVs), viral-associated sequences, are normal components of the human genome and account for 8–9% of our genome. These original provirus sequences can be transactivated to produce functional products. Several reactivated HERVs have been implicated in cancers and autoimmune diseases. An emerging body of literature supports a potential role of reactivated HERVs in viral diseases, in particular viral-associated neoplasms.
I don't think there's a recorded case of such a virus reconstituting itself and being transmitted to another human being, but I don't believe the possibility has been completely ruled out. As the linked article goes on to say, the most recent HERV dates from about three million years ago and includes DNA for all the proteins which make up the virus.
posted by jamjam at 2:34 AM on November 2

If you'll go for fiction, this book by Kim Stanley Robinson might interest you. It explores your question, or something like it.

Short answer: the author of the Mars Trilogy no longer thinks we are anywhere near ready to leave this planet.
posted by aniola at 6:45 AM on November 2 [2 favorites]

Eradicate all viruses in humans and any livestock they take with them, and you'd probably have a good chance of avoiding things like flu and colds. But viruses are an integral part of our body ecology and even embedded into our DNA. You can't get rid of them completely, and they are likely to come back.
posted by 0bvious at 7:02 AM on November 2

Yeah, like a lot a lot. Like as in, our ability for language itself may come from an ancient virus.
posted by aniola at 12:43 PM on November 2

There are viruses that can be dormant for years before hitting a stage when they are likely to infect others. Herpes is the best known of these, and there are tests for it, but there's no reason to think that we even know of all the viruses like that or would be able to test for them.

For bacteria, the human digestive system makes good use of them, so we probably want to keep them around.
posted by yohko at 1:28 PM on November 2

It is also thought that common ancestors of viruses are also a part of our DNA in the form of transposable elements, which jump around our genome and can cause problems.

I didn't really finish this point, which is to say that we carry parasites even aside from a lived experience of infections from outside viruses. If you have space colonization and spacepeople doin' it, the resulting babies inherit their parent's transposons, bits of genomic information which are along for the space ride, parasites just as much as viruses. Some of them can cause developmental disorders in offspring.

To give you a clearer answer: Parasitic genomic information is a part of us, in varying degrees. We're not getting away from it any time soon, even if we leave Earth. (If anything, we're bringing it with us.)
posted by They sucked his brains out! at 1:57 PM on November 2

One more thing, and then I'll bow out: I brought up herpes-family viruses, because they are ubiquitous, and many people are asymptomatic and never realize they were ever infected. HPV is another virus that enters a long latency stage, before some variants seriously raise the risk of cancer.

These are some viruses that we know of. You can rent a yacht like J. Craig Venter did, scoop up some ocean water, and there's just all manner of viral "life" (or viral information) teeming out there. Stuff we really know little or nothing about.

A research consortium called ENCODE looks at the human genome (among others) and tries to measure, roughly, how much of our genetic constitution is actually us (or used for making us work).

That measurement is a complicated and controversial question, depending on which researchers are asked, but the main point is that, whatever the final tally, we seem to carry baggage with us by virtue of millions of years of evolution. We also get exposed to a lot more on Earth by simple virtue of living a typical life — we are social animals, and that brings us into contact with a lot of organisms along the way, which are happy to hop on for a free ride.
posted by They sucked his brains out! at 2:13 PM on November 2 [1 favorite]

My 1-year-old came down with roseola while we were completely isolating. Same thing happened to three other families I know. It was completely baffling, and then I read this:

It totally upended my assumptions about how viruses spread.
posted by messica at 8:22 AM on November 3

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