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If, as a physicist, I were to be told that quarks have never been isolated, and so they are not actually real particles, it would take some effort to respond. I'd have to talk about the Standard Model and Asymptotic Freedom, and thus admit that they do have some properties that are not like other particles.

If faced with insistance that this proves the case, that they are actually some sort of epiphenomenon of particle accelerators, I might have some difficulty knowing how to proceed. It's true that they manifest an as yet new characteristic, and so perhaps we have to expand our conceptualizaiton of what a particle is.

That may not be a perfect analogy for my question, but I have a medical friend who would like to tell me that no virus has ever been isolated, and that as opposed to some kind of transmissible, infectious organism, they are actually some kind of waste product of cells. I am told that any attempt to satisfy Koch's postulates involves the injection of materials in addition to the viruses at issue, and the claim is that it's these combination of materials that is making the animal sick.

I see a lot of varied "viruses don't exist" claims around the web, focused on HIV, measles, and CV19, and associated with names like Drs. Stefan Lanka, Andrew Kaufman, Tom Cowan, etc. Associated claims are that in any context that involves supposed exposure to a virus, less than 100% of the animals get sick, and so whatever may be going on, it's the animal itself at issue. In some quarters this is called "Terrain Theory." I would like to not have to dig too far into this.

How can I respond in a coherent way that doesn't require becoming a virologist?

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    – Chris
    Commented Jul 17, 2022 at 10:39

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It is very easy to disprove their claims, but the burden of proof doesn't lie with you, it lies with the person making the claim. If they want to claim that there is a "cell waste product" that causes the widely varying symptoms and viral effects (in cells, model organisms etc) we see with different viruses (compare say chickenpox with SARS-CoV-2), then they need to prove that this is the case. They need to do the science and have it passed through peer review etc. Also remember that extraordinary claims require extraordinary proof - they need to prove the whole scientific consensus wrong in this case!

At its most simple, you can purify viruses via a range of methods (e.g. ultrafiltration, ultracentrifugation, chromatography etc) and resuspend in a simple salt solution of varying compositions (e.g. phosphate buffered saline, ringer's solution, tris buffered saline) and use that purified virus to infect. I would hope that even the most science-denying person would see that these solutions are very simple and don't contain anything special that could be "cell waste" or "its the fetal bovine serum" (another virus-denier claim). I would note that most of these denier people wouldn't understand the principles behind the above methods, but using them you can get pure preparations of viruses and other materials, down to separating out single molecule types from a crude solution.

You also run controls of the solution alone and easily see that the animals/cells don't infect at all with these controls, but do infect with the virus containing material. You can also run controls on your sample prep - for example, treat uninfected cells to the same virus preparative procedures as you did for the virus and show that this also doesn't result in infection.

If it were a product of cell waste you would expect to see these effects from all cells, not just virus infected ones. For a cell waste you should also see some sort of dilution effect that is non-propagable (i.e. can't be passed on) - take your purified virus and dilute it in your solution of choice and it will still infect, but "purified" material from un-infected cells won't.

An additional note: You can also take the genetic material of the virus and use that to produce more virus. In some cases (as with positive sense RNA viruses and DNA viruses) you can use the genetic material directly and produce more viruses with the same characteristics as the source of the genetic material. Now, it doesn't work for some viruses - some genomes are too big, need special conditions, etc., but it does surpass some of Koch's postulates, as in you can synthesize this genetic material in the lab and using that material along with cells to produce a virus with exactly the characteristics of the original source of the genetic material.

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    $\begingroup$ The trouble is, the "burden of proof" claim may be formally correct but it is not necessarily rhetorically persuasive - and moreover it leaves any third parties to the dispute who are ignorant of the arguments on both sides hanging as to becoming better informed about what and why certain things should be believed. Someone could say, "sure, they haven't proven their case, but because xyz, why should I believe the 'mainstream' side either? " $\endgroup$ Commented Jul 16, 2022 at 6:09
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    $\begingroup$ @The_Sympathizer I totally agree - and it definitely is a problem, which is why the rest of the post is there... $\endgroup$
    – bob1
    Commented Jul 17, 2022 at 4:29
  • $\begingroup$ Very good answer. Much appreciated. The various forms of "isolation" and the control methods are sufficient to what I was looking for. Also, I've read some history of koch's postuatels, and see that they were criticized almost right away. $\endgroup$
    – Diagon
    Commented Jul 25, 2022 at 5:58
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This may be too brief or simplistic, but a short discussion of electron microscopy might be in order; the different viruses are consistent in morphology in the diseases they cause (e.g. Ebola virus, smallpox, COVID, etc.)

It’s hard to argue with your own eyes (or a mental picture of what your eyes would see…)

To quote from a paper on the subject:

Using TEM, viruses can be differentiated by their ultrastructure: shape, size, intracellular location and for some viruses, by the ultrastructural cytopathic effects and/or specific structures forming in the host cell during their replication. Ultrastructural characteristics are usually sufficient for the identification of a virus to the family level.

And

For some viruses, TEM can be conducted on contents of skin lesions (e.g., poxviruses and herpesviruses) or on concentrated stool material (rotaviruses and noroviruses). For successful detection of viruses in ultrathin sections of infected cells, at least 70% of cells must be infected, so either high multiplicity of infection (MOI) or rapid virus multiplication is required.

If you know any cell biology. Viruses can’t be mistaken for cells or detritus.

enter image description here

What cell or piece thereof can the above be? Great picture of bacteriophages.

enter image description here

Ebola virus. Always present in Ebola, not present in other illnesses.

Electron Microscopy in Discovery of Novel and Emerging Viruses from the Collection of the World Reference Center for Emerging Viruses and Arboviruses

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    $\begingroup$ +1, best way to prove something exists is to go take a picture of it. $\endgroup$
    – Topcode
    Commented Jul 15, 2022 at 3:16
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    $\begingroup$ Excellent - the beauty of EM is that the capsids are so consistent with the species - and of course phages are only found in bacterial preps and look nothing like exosomes. I also really really wonder how the capsids of the filoviridae evolved, must be some significance to be so distinct. $\endgroup$
    – bob1
    Commented Jul 15, 2022 at 9:04
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    $\begingroup$ @bob1 A bacteriophage is a wondrous thing, isn’t it? Such a tiny, ‘simple’ thing, but so elegant and dangerous to the bacteria it targets. Amazing! $\endgroup$ Commented Jul 15, 2022 at 14:00
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    $\begingroup$ @anongoodnurse absolutely, couldn't agree more. The diversity is incredible too, not to mention the abundance $\endgroup$
    – bob1
    Commented Jul 15, 2022 at 22:49
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At this point, anyone who doesn't accept the existence of viruses has reached flat-Earther levels of delusion and probably cannot be convinced otherwise by any evidence you would show them or any argument you can make. To believe that viruses are not the explanation for most diseases attributed to viruses, you have to believe in a vast conspiracy among government institutions, scientists, hospitals, pharmaceutical companies, and various commercial enterprises. If you think such a conspiracy is more likely than viruses doing what science says they do, then your method of weighing evidence is quite strange and, I'd say, wrong. There are many compelling sources of information that viruses are real. Even if you refuse to accept one of these sources, the others should be enough to convince you that the existence of viruses is more likely than such a massive conspiracy.

  1. First-hand knowledge. Believing in a flat Earth requires rejection of evidence of an approximately spherical Earth that can be obtained firsthand (ships on the horizon, lunar eclipses, flights from Santiago to Auckland, flights from Johannesburg to Perth). Even more so (and unlike quarks), most people have first-hand experience with viruses, observing spread of colds, flu, chicken pox, and COVID-19 within families and people in close contact. It's pretty hard to explain this fact without proposing some kind of microscopic replicating organism-like thing that passes from person to person. Even if you don't believe that the viral particles are carrying these diseases, it should be clear to everyone that they are contagious diseases.

  2. Changes in society in recent memory due to understanding how viruses work. Major early support for the existence of viruses came from the fact that vaccines work, which I am guessing virus-deniers don't accept. Vaccines are based on treated viral particles or components of viral particles (viral proteins, sometimes called toxoids). There are people living today who remember a time when people lived in fear of polio and measles was a common childhood illness. You can easily find history discussing the small pox and measles epidemics. What happened to those diseases if viruses aren't real and we don't understand how to combat them?

  3. Pictures of viruses. If you think they are computer generated or something, you can probably talk to someone at your local university who has taken a picture of one. Taking pictures of viruses is easier than taking pictures of a round Earth. You only need a relatively low quality electron microscope, which you can get for less than $100,000.

  4. Understanding viruses enables other technology. For many viruses, we understand the components that make them work. Besides vaccines, there are other technological uses of viral components. Retroviruses such as HIV must have a protein that copies RNA to DNA. You can buy such a reverse transcriptase to copy RNA yourself. Viruses are also used in gene therapy and you can contract with a large number of companies to create viral vectors with your custom gene. If we didn't understand viruses, why would people buy and sell this stuff?

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Koch's postulates are only somewhat more relevant to modern medicine than insisting that electromagnetic waves must travel in some medium (luminiferous aether) is to modern physics. They do not describe necessary and sufficient conditions for proving that viruses cause disease, they're postulates that someone came up with over a century ago and were proven insufficient by subsequent investigation. They're not laws of nature, and any argument assuming that they are necessary and sufficient conditions to prove that a given pathogen causes a given illness is meaningless.

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    $\begingroup$ I'd argue that Koch's postulates are sufficient but not necessary to prove that a given pathogen causes a given illness: if you've got a pathogen that meets the criteria, it's reasonable to assume that it's the cause, but if you've got a pathogen that doesn't, you can't rule it out as the cause. $\endgroup$
    – Mark
    Commented Jul 14, 2022 at 21:09
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    $\begingroup$ It's worth noting that Koch's postulates don't always apply to viruses, and that alternative postulates have existed for nearly a century to better identify putative viral pathogens. See Why did Rivers replace Koch's postulates? $\endgroup$
    – acvill
    Commented Jul 15, 2022 at 14:52
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    $\begingroup$ I read about this, thanks @acvill . Beyond Rivers, I also found Koch's Postulates in the 21st Century. $\endgroup$
    – Diagon
    Commented Jul 25, 2022 at 6:01

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