32
$\begingroup$

I'm not a biology student at all, but I'm trying to get a clearer picture on what is meant by "virus cannot survive after a certain period".

To my understanding, a virus cannot be killed it can only be inactivated (for example, by means of heat and lowered pH).

So I really don't understand how can virus get inactivated by just being on a certain surface for an extended period.

I've come across numerous articles which told me virus won't survive on a surface. They usually focus on comparing the survival time between different types of surfaces but never touch on how the virus gets inactivated.

Can someone help me understand the "how"?

$\endgroup$
  • 3
    $\begingroup$ Related: 2019 Novel Coronavirus (nCoV) lifetime outside an organism $\endgroup$ – dotancohen Jan 29 at 12:55
  • 3
    $\begingroup$ "To my understanding, virus cannot be killed" This is just because they're generally deemed not to be alive in the first place. $\endgroup$ – ceejayoz Jan 30 at 13:44
  • $\begingroup$ It does depend on the surface, and the virus, different ones are destroyed in different ways. A virus survives in the same way an antique car survives, as in it still exists in good enough shape to function. $\endgroup$ – John Jan 30 at 20:33
49
$\begingroup$

Many important viruses are coated with a lipid envelope and rely on this to enter the host cell. This envelope is fragile - it's similar to a soap bubble - and it can be disrupted in many ways. Lipids will oxidize in air over time and this will degrade their ability to maintain an envelope. Surfactants such as soap or solvents such as alcohol will disrupt an envelope quickly. Even if the genome inside survives, if the envelope is disrupted the virus won't be able to infect cells. The exact mechanism of inactivation likely varies a lot from virus to virus, and hasn't been studied extensively. This paper found that Hepatitis C virus RNA survived alcohol treatment, but lost infectivity, presumably due to envelope disruption. In contrast, heat treatment (80°C) destroyed both the envelope and the RNA.
Another paper found enveloped viruses survived being dried out a shorter time than non-enveloped viruses. (5 days vs. weeks)

Speaking generally, the environment outside a body is hostile! If you were taken out of your home and dropped somewhere in the wilderness, there's many different ways you could die, and it's more remarkable if you survive. A similar situation arises for viruses.

$\endgroup$
  • 5
    $\begingroup$ +1 To be fair I don't think the last paragraph is a good comparison, as a virus is just a bunch of molecules and not a living thing. And I think it's from this understanding that the original OP asked his question. If you put a table outside on a surface it won't get destroyed either. Obviously the answer is "viruses are relatively fragile, because evolutionary the advantages of surviving away from organisms that could replicate them was fairly pointless" . Does make me wonder whether with the increased population density of human organisms there will be a point where it's worth surviving. $\endgroup$ – David Mulder Jan 29 at 12:08
  • 12
    $\begingroup$ The point I was trying to make is that viruses are complex systems that have many potential points of failure. In that regard, they are closer to a living thing than a table, which can take a lot of damage and still function as a table. Maybe a better comparison would have been to some electronic device like a PC that you'd expect to stop working if its left outside. But, I expect rain would destroy it before anything else 99% of the time so it doesn't work the same way. $\endgroup$ – timeskull Jan 29 at 15:28
  • 1
    $\begingroup$ @DavidMulder: To give a better analogy, a virus is like a car that functions well in the city but will break down gradually if left into the wilderness, rapidly if it is thrown into a pond or the sea. Similarly, viruses 'survive' well in their hosts, but will gradually break down if left outside, and rapidly so in certain environments. $\endgroup$ – user21820 Jan 30 at 4:03
  • $\begingroup$ @DavidMulder Even with the table, leaving it outside under the sun / rain / snow etc. versus leaving it in your home over a long period of time means different rates of degradation. $\endgroup$ – John Hamilton Jan 30 at 10:59
  • $\begingroup$ @DavidMulder I would argue that there's a fine line between a "bunch of molecules" and a "living thing". The death of a "living thing" is just what happens when a sufficient number of internal systems of the thing (which are themselves "bunches of molecules") are placed in hostile scenarios for a sufficient time for them to cease function. I would think the comparison of a virus on a surface to a human in a desert is apt (if incredibly simplified) - the concept of "death" might be different from a micro to a macro scale, but the ultimate result is the same for the subject. $\endgroup$ – Abion47 Jan 31 at 21:01
23
$\begingroup$

Ultraviolet (UV) light emitted from the sun has enough energy to break chemical bonds in DNA and RNA.

Some frequencies of UV light can cause damage in the DNA in skin cells that can lead to replication and expression errors, which lead to cancer (melanoma).

Similarly, UV can break up and inactivate the genomic payload of a virus:

Sunlight or, more specifically, solar UV radiation (UV) acts as the principal natural virucide in the environment. UV radiation kills viruses by chemically modifying their genetic material, DNA and RNA. The most effective wavelength for inactivation, 260 nm (55), falls in the UVC range, so-named to differentiate it from near-UV found in ground-level sunlight, i.e., the UVB and UVA portions of the spectrum, 290 to 320 nm and 320 to 380 nm, respectively (51). Nucleic acids are damaged also by UVB and UVA but with lower efficiency than by UVC radiation (64).

Surfaces exposed to sunlight would see partial to complete inactivation of virus particles over time.

There is a paper here that discusses using a safer frequency of UVC radiation as a biocide:

The biophysical reason is that, due to its strong absorbance in biological materials, far-UVC light does not have sufficient range to penetrate through even the outer layer (stratum corneum) on the surface of human skin, nor the outer tear layer on the outer surface of the eye, neither of which contain living cells; however, because bacteria and viruses are typically of micron or smaller dimensions, far-UVC light can still efficiently traverse and inactivate them13,14,15.

$\endgroup$
1
$\begingroup$

Like other forms of life, viruses are composed of fragile molecules susceptible to damage from the environment. They may oxidize in the air, suffer mechanically stresses, be hit by UV light, etc. Metabolism in cellular life combats this effect by actively making repairs and by forming and maintaining protective barriers.

Viruses don't do that. Outside of a cell, they don't do anything. They don't have a metabolism. They can't make repairs. The damage accumulates until they can't work anymore.

$\endgroup$
  • $\begingroup$ Welcome to Biology.SE! Your point about viruses not be able to make repairs is a good one, but answers are much more likely to receive a favorable response if you include supporting references (primary literature is best). Without that support, your answer is indistinguishable from opinion. ——— Please take the tour and then consult the help pages for additional advice on How to Answer effectively on this site and then edit your answer accordingly. Thanks! 😊 $\endgroup$ – tyersome Feb 4 at 3:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.