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Plant Viruses DO NOT Infect Mammals
This paper was brought to my attention by Prof. Gary Foster (http://www.bristol.ac.uk/biology/people/gary-d-foster/overview.html) on Twitter. The research group behind it claimed Tobacco Mosaic Virus (TMV) can infect mice lungs. That's what they claimed but that's not what their study actually showed. There are plenty of reasons to not smoke, but being infected with a plant virus is certainly NOT one of them.

Firstly, I must point out that TMV is an extremely stable virus (see the links at the bottom of this post). It can persist in the environment for a very long time and stay infective (to mostly solanaceous plants). When placed in storage at 4°C/40°F, they can remain infectious (to mostly solanaceous plants) after 50 years. And that's how they spread - they are able to persist in the environment and contaminate anything which may come into contact with a host plant. To be able to do that, it must be very stable and not easily altered or destroyed by anything going on around it.

What this research group basically did can be summed up with this:
"Eh, so we got some TMV, stuck 'em in the lungs of some mice, and guess what? When we dissected the mice later, we found TMV in their lungs! Isn't that odd?"

No. As mentioned above, TMV is extremely stable and persistent in the environment. If you stick TMV in the lungs of mice, of course you are going to find TMV in there! Furthermore, the virus did not activate, nor did it infect the mice's cells. The mice with TMV in their lungs showed an immune reaction, but that would happen even if it was some non-biological particulate matter.

After they sacrificed the mice, they mashed up their lungs (which had TMV in them) and dabbed the resulting fluid on some tobacco plant and what do you know, the plants developed a viral infection! Which only goes to show how stable TMV actually is - NOT that the virus infected mice lungs.

Here's the take home message: Plant viruses are plant viruses and they CANNOT infect mammals, or even just animals in general - plants and animals are simply too biologically different for that to happen. 

Here are some reference on the stability (and other aspects) of TMV: 
http://www.apsnet.org/edcenter/intropp/lessons/viruses/Pages/TobaccoMosaic.aspx
http://extension.psu.edu/plant-disease-factsheets/all-fact-sheets/tobacco-mosaic-virus-in-greenhouses
http://www.plantcell.org/content/11/3/301.full
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28 comments
 
A friend of mine told me his grandfather died from that because he grew his own tobacco which got chicken shit on it, grew the spores and they grew in his lungs, if this is the same issue
 
No, those are probably fungal spores - not plant viruses (which can only infect plants).
 
No that's okay. We just thought this paper made some very misleading and baseless claims and we want to get on its case before some press headlines start screaming all kinds of nonsense about plant viruses jumping into human or some crap.
 
Understand you. The press can cause all sorts of misinformation
 
Yeah, especially when it comes to stories about science.
 
I don't believe anything outside of local news services for much of anything actually.
 
Well, I guess we're having a separate conversation about news coverage and media now as opposed to the OP...
 
Well I mean in general, not anything specific.
 
Umm, okay? I was hoping that the comments would relate back to the OP seeing as that the reason I posted about this study in the first place.
 
It's Ok. I understand that and I wish you the best. I'll share it to help.  :-)
Tai Mi
 
+Tommy Leung - do you mind if i post this to facebook (with all credits, of course)? I have a friend on there who worked with TMV a while back that would be interested in this.

So...if they mashed up the lung tissue, that combined everything, misconstruing the results. Do you know if the method of testing was ever revised to avoid the mixing?
 
+Tai Mi sure, you can post it to facebook. I've made this a public post and tweeted about it too, so go ahead. You friend  will know this better than I, but I'd say the only thing they really demonstrate with the paper is that TMV can remain infective to their actual host (plants, and in this case their test host was tobacco plant) after being mouse lung slurry - which is not too surprising considering how persistent it is in the environment anyway.
 
Thank you. Wish I never smoked a cigarette in my life, but I do. Will be glad if cigarettes did not exist. But using false information only gives fuel to those opposing you.
 
Oh, thanks for this. I hadn't seen it and I fully expect it to be misused but the usual suspects.
 
What sort of methodology would be able to demonstrate/rule out that a given virus is infective for animal cells?  Is it all based on some kind of marker gene expressing or...?  (I feel silly even asking, since I've actually used TMV for VIGS work in plants; the tests were carried out on expressing a GUS gene or silencing a chlorophyll-related gene.)
 
It seems to me that any concerns about transmission of plant viruses raised by any "usual suspects" would, given the way that this paper itself presents their data be fairly legitimate, and therefore, would not actually constitute "misuse".   My point being that the communication fail here lies within the realm of scientists.  Open access publication, (and press releases) can be good things, but care needs to be taken, in these public venues to ensure that scientific observations are carefully presented and not sensationalized.
From the point of view of the public at large, catigating "usual suspects" who might further publicize this article would be counterproductive, IMHO. 
What needs to be seen is more articles like this one, that demonstrate that science is self regulating.
 
+Gaythia Weis : we've just seen this merry-go-round with a "toxic killer plant virus" that was based on the complete misuse of the CaMV paper that came out. It was not sensationalized by the scientists who wrote the paper, but the "usual suspects" completely misused the information to yell fire in a crowded theater--100% contrary to what the paper's authors concluded.

It doesn't really matter what you think about what's counterproductive. It will be misused anyway.
 
+Kaikki Kasvissa , what is needed to show that a plant virus can infect animal cells are two things. First you would need to show that the virus can replicate inside the animal cell, not just persist. And second, that it can move to other cells to continue the infection. In this paper the virus count went down dramatically very fast, a quick suggestion that they were not able to replicate and infect other cells.
 
+Mary Mangan   In my opinion what matters for good science communication is that scientists take care (and put peer pressure on other scientists to take care) to see that new findings are phrased in a manner that states their position within appropriate limitations, and doesn't wrongfully raise concerns.
What is not clearly defined in the PLOS article is the distinction between their work, and what +Gustavo MacIntosh and +Tommy Leung outline above as needed to prove actual infection in lung cells.

Without being a virologist, since this the first part of this sentence is true:
"Although we did not evidence TMV replication in mouse lungs or murine macrophages in the present work, our findings raise concerns about the potential interactions between TMV and human hosts."
I would say that this one is not, at least not yet, true:
"Until now, a major issue that precluded considering plant viruses as potential pathogens in humans was that they could not enter and replicate in vertebrate cells."
Of course, +Tommy Leung does a much abler job of dissecting the article above.

IMHO, the way to combat those who may be prone to "yell fire in a crowded theater" is not to jump up and down and point fingers at them, that only gives them the publicity they desire.
Thoughtful posts, such as this one by +Tommy Leung serve several positive purposes.  They act as controls on the scientific community itself, by bringing issues with published research forward where it can be discusses by the science community at large. 
But also, it brings these issues to the attention of the science interested public.  This is crucial in enabling those people to share the information with others.  but very significantly, it also is a demonstration as to how science is self policing.  This offers important lessons in skepticism and science.

It is the jousting that I think is counterproductive.
 
We must be operating in different spheres +Gaythia Weis. The cranks need no help from a G+ thread for publicity, nor did they get any. They have a quite effective network of allies that spread misinformation.

And your distaste for jousting is fine--you are free to not participate. But when I see misinformation--and that will be inevitable, I like to counter it.
 
+Gustavo MacIntosh...well yes, of course they need to show the virus can replicate, but all such information is inferred from the experimental system itself.  I intended the question more at this nitty-gritty level.  In plant systems this is done with GUS or silencing of genes that give obvious phenotypes (and from personal experience I feel this kind of assay is less reliable with expression of a transgene than silencing of an endogenous gene).  So what is considered a good viral replication assay in a mammalian system?  Would a recombinant virus with GFP spreading across a cell culture be sufficient to demonstrate the point, for example?
 
plant viruses are extremely abundant within humans. Here's an excellent example from human digestive tracts. The viruses are able to re-infect plants after passing through a)food processing and b)the human GI tract.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1310650/
Therefore finding plant viruses in humans is pretty par for the course. So far the possibility of plant viruses replicating and causing disease in humans is unheard of, especially given the many millenia that people have been in contact with these agricultural crops in which these viruses are highly abundant. TMV is everywhere there is major agriculture, and abundantly used in research. If one of the scientists working with the TMV ever got infected with it, we'd know it by now.
 
Rybicki's effectively demolishes the way in which the authors ended their abstract:  "which raises questions about the potential interactions between TMV and human hosts."  in his opening sentences.   It is that abstract conclusion that is going to lead to misapprehensions on the part of less informed readers or media representatives skimming through this publicly posted document.  The popular science media is, in turn, probably apt to add layers of exaggerated concern to draw attention to their own writing.

Rybicki's answer to concerns about potential "alarmists" is to shrug them off.  But scientists actually need the support of the public to function, since that is the ultimate source of many research dollars. An unending diet of scientists say this/no they didn't in the media leads to cynicism. Frequently the hype starts with the scientists or with the PR department of their research institutes and universities.

 At the same time, a lot of research  does create along the way a lot of fairly mundane results and even dead ends.  And these are frequently, although not always, worth investigating and reporting.  If we want the public to understand that science is a process, and the proper functioning of that process depends on enough financial support to follow new leads even though some of those end up with less than exciting conclusions, then we are going to have to figure out ways to communicate more of the process and less of the hype.
 
+Kirk Flowers Spores do not = viruses...spores = fungi.  Or sometimes bacteria.  Which MAY infect lung tissue.  However, and I hate to say this, growing and smoking your own tobacco...like eating organic vegetables, = stupid.
 
+Ed Rybicki That's a stupid comment. How is growing any plant 'stupid'? As far as eating organic vegetables I eat them out of the garden all the time. Does that make me 'stupid'?
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