I am posting a question that a friend of mine has asked. My friend wrongly assumes that SARS-CoV-2 virus can be transmitted through blood, although there is no such evidence. However, his question remains a valid one.

With so much news about COVID-19 all around us, I have been doing some study on viruses. I do understand that viruses are not really living creatures. They just have some genetic information, which they can pass on to the host cell, causing the virus to proliferate, and in some cases interfere with the normal functioning of the cell. Outside of a host cell they are completely inert. In fact they show all the traits of a non-living entity. I get that.

My question is based on the following scenario. Imagine there are two doors, next to each other. Let’s call them A and B. There is a door knob on each. A COVID-19 patient sneezes near the doors, and some SARS- CoV-2 viruses land on each door knob (i.e. door A and door B).
Unfortunately within a few hours someone with a cut finger touches the knob of door A and gets infected. So far no dispute.

Fast forward 5 years. In the meantime the knob on door B never got cleaned/wiped. In other words, the inert viruses are still on the door knob. Again someone with a cut finger touches the knob of door B but in this case the person does not get infected. Why?

Obviously something happened to the virus during these 5 years that caused it to lose the ability to pass on its genetic information to the host cell and replicate. What exactly happened?


We received a response for the query that seemed reasonable to us but was voted down, and presumably deleted by the author. Fortunately I was able to recover a screen capture. To keep the discussion going, I would like to temporarily include the response here till a better response is posted. Here it goes:

This isn't very professional, but there are the basics. Viruses are obligate parasites, which means they can't live outside a host (in this case, a cell) for long. Viruses get damaged as everything else, the damage taking many forms, such as hydrolysis, photolysis, free radical damage, reaction with other molecules (like detergent), conformation changes, dehydration, maillard reactions, and changes induced by heat of labile molecules (like decomposition). All types of damaging processes happen at an increased reaction rate with increasing light and heat. Viruses have rudimentary repair mechanisms if any, so it's a matter of time before they become inactivated. A damaged virus entering the body wouldn't be able to do much harm if any, as their genetic information would be damaged beyond repair, and so, not able to be replicated to make more viruses. Their proteins and genetic bits would still trigger an immune reaction and immunize against intact and not very damaged viruses (which is why damaged viruses are used in vaccines). Those damaged viruses that remained outside just become microbe food.

  • $\begingroup$ Yes, disputed. The virus is not circulating in the blood stream (as far as we know), it is replicating in the cells of the airways. $\endgroup$
    – Chris
    Mar 9, 2020 at 15:27
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    $\begingroup$ Any answer for the basic question: what causes (non-living) viruses to die outside of host cells? $\endgroup$
    – Sandeep
    Mar 9, 2020 at 15:31
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    $\begingroup$ They don't die since they are not alive. $\endgroup$
    – Chris
    Mar 10, 2020 at 5:52
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    $\begingroup$ I don’t think that including a deleted response in a question is appropriate. If the person deleted it you should respect that. And a question is a question, not a discussion to “keep going”. Finally, it is not acceptable to post text as images as it discriminates against those with visual difficulties. $\endgroup$
    – David
    Mar 10, 2020 at 17:34
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    $\begingroup$ A similar question has been answered here: biology.stackexchange.com/a/89953/55506 $\endgroup$
    – timeskull
    Mar 10, 2020 at 18:44


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