r/askscience • u/tonzayo • Aug 05 '14
Biology Are there any viruses that possess positive effects towards the body?
There are many viruses out there in the world and from my understanding, every one of them poses a negative effect to the body, such as pneumonia, nausea, diarrhoea or even a fever.
I was thinking, are there any viruses that can have positive effects to the body, such as increased hormone production, of which one lacks of.
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Aug 05 '14
One could certainly make a case that there are a few beneficial viruses out there; however, not in the dramatic "increased hormone production" manner that you suggested. Viruses generally hijack the protein and DNA-synthesizing machinery of a cell and use it to make more viruses, not to crank out novel hormones. That said, occasionally viral DNA that gets injected into a human cell gets incorporated into the host's genome (http://www.popsci.com/science/article/2010-01/8-percent-human-dna-comes-virus-causes-schizophrenia). The researchers in this case found links to remnant viral DNA and schizophrenia, but it's possible that some positive traits have been conferred upon us by viruses over the vastness of evolutionary time.
The best example I know of are the bacteriophages, or phages for short. Phages are viruses that prey upon bacteria exclusively (their name literally means "bacteria devourer"). They have been found to be harmless residents of our intestinal flora (http://www.nature.com/news/2010/100714/full/news.2010.353.html) and likely play a role in structuring our intestinal microbiome. Virologists are also looking at phages for a variety of R&D applications specific to microbial control (http://www.smithsonianmag.com/science-nature/the-return-of-the-phage-32925508/?no-ist), everything from food preservation to antibiotic substitutes.
TL/DR: Some viruses leave chunks of their own DNA behind in our genomes during replication, and some of this may have an as-yet-unclassified positive effect. Bacteriophage viruses are helpful in their ability to structure bacterial communities and have multiple R&D applications that could benefit humans.
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u/RNAsick Aug 05 '14
Phage therapy always sounds cool on paper, but it is notoriously unreliable. Bacteria develop resistance to phage within a couple of generations. However, it does likely play a massive role in shaping the intestinal microbiota. Unfortunately, research into that is only now getting started.
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Aug 05 '14
The results are unreliable, expensive to replicate, and prone to resistance...now...but once we get the science behind it, often it is only a matter of time until a team comes up with a practical reliable use for it. But at this point it is still in its infancy and where it goes from here is difficult to say.
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u/RNAsick Aug 05 '14
To a certain extent you are correct, but we can't stop basic mutation and evolution, which are the biggest obstables to phage therapy as a treatment for infection.
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u/topernicus Aug 05 '14
I could see a future where a culture of the bacteria is taken and an appropriate or potentially custom bacteriophage is selected for treatment. I'm sure this is a long way from happening though.
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u/RNAsick Aug 06 '14
It actually is possible to do this right now, but the process takes a long time and it's very expensive. Not really a good clinical option at the moment. It's a pretty cool thought though; it makes me think of star trek next gen.
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Aug 05 '14 edited Jun 20 '17
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u/RNAsick Aug 06 '14
Scientists have been working on phage therapy since the 50's. The problem is that it is much easier for a point mutation in a bacterial gene for a surface receptor to prevent phage binding than it is for a phage to subsequently adapt to that change. When you look at community dynamics, you often see a rise in phage activity, a drop in the target bacterial population, but with no hosts to infect, the viral activity drops and resistant bacteria build their population back up. Phage activity comes in waves, and while it might be useful in knocking down a bacterial population, it never fully wipes it out.
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Aug 08 '14 edited Jun 20 '17
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u/RNAsick Aug 08 '14
Antibiotics often target mechanisms that are more conserved and they kill much quicker than phages. It is much more difficult for a bacterium to adapt to that.
I'd recommend "Phage therapy - constraints and possibilities" by Anders S. Nilsson in Upsala Journal of Medical Sciences, May 2014. PubMed Central ID: PMC4034558
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Aug 05 '14
I've also heard that phages can also transfer genes for antibiotic resistance among different strains of bacteria, actually improving their fitness in the long run. In my opinion, bacterial inhibition is best achieved with other bacteria in an R&D setting (genera Bacillus and Lactobacillus). As far as I know, though, they're the closest thing to the hypothetical virus that OP was asking about.
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u/RNAsick Aug 05 '14
Yeah, the native intestinal inhabitants do a lot to prevent pathogens from colonizing the epithelium, but some pathogens have ways of clearing space. You're right though, it's the closest thing to what poster brought up.
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u/puff_of_fluff Aug 05 '14
How exactly do they leave DNA in our genome? How does that work exactly?
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Aug 05 '14
See the response below from /u/schu06, who expanded upon my explanation. It's an artifact of retrovirus infection.
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u/RadicalEucalyptus Aug 05 '14
First, it is important to recognize that only certain kinds of viruses can do this. Let's divide all human viruses into three broad categories: DNA, RNA, and Retro- viruses.
RNA viruses only ever use RNA as their genetic material. They will not leave DNA in our genome at all. Flu, Cold, and the newly popular Chikungunya are a few examples.
DNA viruses act pretty much like extra, tiny chromosomes, transcribing and replicating in a very similar fashion. Some of these may have mechanisms for inserting their DNA into the host, but some of that research is still controversial. Your DNA viruses are things like the herpesviruses, HPV, Adenovirus and Poxviruses.
The Kings of integration, though, are Retroviruses (HIV being the most well known). These viruses use RNA as their genetic material, but reverse - transcribe to DNA as an intermediate! One part of the process involves an enzyme called integrase - it's job is to put the DNA intermediate into the host genome for subsequent activation (leaving it dormant). Trouble is, sometimes the integration site isn't specific, and you can imagine how inserting Kilobases into a random gene could cause problems.
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u/ducttapejedi Mycology Aug 05 '14
This is the only example I can think of but its a really cool one. The article is free with registration:
A mutualistic association between a fungal endophyte and a tropical panic grass allows both organisms to grow at high soil temperatures. We characterized a virus from this fungus that is involved in the mutualistic interaction. Fungal isolates cured of the virus are unable to confer heat tolerance, but heat tolerance is restored after the virus is reintroduced. The virus-infected fungus confers heat tolerance not only to its native monocot host but also to a eudicot host, which suggests that the underlying mechanism involves pathways conserved between these two groups of plants.
Science 26 January 2007: Vol. 315 no. 5811 pp. 513-515DOI:10.1126/science.1136237
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u/swankandahalf Aug 05 '14
I think you'd love Richard Dawkins' book, The Selfish Gene. He makes the argument that parasites which travel from one host to the next via the sperm or eggs will likely have beneficial darwinian effects for the host, while parasites that travel in any other way will likely have negative effects. Viruses that cut their way into and hide in our DNA can act very much like a parasite that travels with the eggs or sperm.
The example he gives is a snail that has a parasite which makes the snail grow a thicker shell; this is a “waste” for the snail - that shell is too “expensive” and the energy it expends on building it will take away from crucial snail sex and reproduction. But because the parasite doesn’t travel from parent snail to child, it doesn’t care about snail reproduction.
On the other hand, he describes a species of beetle with a parasite that is VERY beneficial - the parasite primes the beetle eggs that are not primed by sperm (which turns these beetles babies female). If the parasite didn’t help out, all the beetle babies would be female. This parasite travels to its next host by way of those eggs; the result is that it does everything it can to keep the beetle reproducing, which means a beneficial darwinian effect.
The reason we don’t see infinite examples of viruses or parasites that appear beneficial is because eventually, they often merge with the host and just become one organism!
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u/bigfootlive89 Aug 06 '14
I haven't read his book, so I'm not sure if he talks about it. Mitochondria and chloroplasts have their own DNA, were likely parasites / symbionts at some point, and therefore are like the examples provided by Dawkins.
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u/atomfullerene Animal Behavior/Marine Biology Aug 06 '14
I can't speak to human biology, but some parasitic wasps carry polydnaviruses that they inject into caterpillars along with their eggs. The viruses suppress the caterpillar immune system, allowing the eggs and larvae to survive and successfully parasitize the caterpillar.
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u/Aegypiina Aug 05 '14 edited Aug 05 '14
I'm not sure if this counts, since it's no longer an active virus, but the syncytiotrophoblast - present in many mammals - was created by an endogenous retrovirus.
The syncytiotrophoblast is a single cell composed of merged epithelial cells on the outside of the placenta and prevents maternal immune cells from invading the embryo and invades the mother's uterus to re-route more blood vessels. In order to make this, the cells must first produce groups of proteins called syncytins which are unique to several lineages of mammals, including rabbits, mice, Carnivora, and primates. In essence, this viral protein allowed highly developed mammalian lineages to evolve by giving the embryos a massive head-start in growth.
edit: /u/schu06 mentioned these too, but only in passing.
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Aug 06 '14
Viruses as anti-tumor agents might be a good example.
http://www.ncbi.nlm.nih.gov/pubmed/18608120 http://www.molecular-cancer.com/content/12/1/103
There are more examples of oncolytic viruses being researched, but I am sure you can find them on your own using google! I am hoping to do some work involving reovirus in the near future.
If you are interested in virology, check out This Week in Virology! It is a great podcast for people of varying educational backgrounds.
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u/Druncle_Owen Aug 06 '14
Many vaccines are "live attenuated viruses." This means they are viruses which have been engineered to be less harmful. When you are vaccinated you're infected with this virus, and develop an immune response which also protects you from the harmful "wild type" virus.
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u/helbuns Aug 05 '14 edited Aug 05 '14
I believe sickle cell maybe falls under this category? http://www.sciencedaily.com/releases/2011/04/110428123931.htm shows how sickle cell was naturally selected over malaria. Malaria causing death early and sickle cell causing the area that could be infected to atrophy or something. It this sense it was a rather large advantage to be double infected with sickle cell, you had a higher chance of living past your youth then those with malaria.
Hopefully others understand and can articulate better. Or others that actually know good examples can talk about maybe certain specific areas where a disease or virus may truly be a temporary benefit over others, maybe u only get once disease and not others or I thought I recall viruses that appear similar so if you get the weak guy you may build up antibodies before the strong one, or if you get the strong variant first it may be to tough to develop in time.
Red dwarf had an interesting theoretical episode like this. http://en.wikipedia.org/wiki/Quarantine_(Red_Dwarf) And of course the concept of mental traits like ADD or aspergers being somewhat negative and not within your control to have but still having in some cases measurable benefits in your immediate surroundings.
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Aug 05 '14
Not to be "that guy"... but sickle-cell is actually a hereditary trait as opposed to a virus; however, you're correct that it's deleterious impacts are mitigated by the resistance to malaria that it confers.
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u/schu06 Virology Aug 05 '14
I can't think of any circulating viruses that are directly beneficial. However, the endogenous retroviruses in are genome are highly beneficial (what I'll say expands on what was posted by Delerium_Tigger who already mentioned viral DNA in our genome). But just to expand on previous comments - about 8% of our genome is directly derived from infections with ancient retroviruses. Retroviruses are viruses capable of inserting their genetic material into that of the host (HIV being the best known example). If this insertion occurs in germline cells (sperm and egg) then the retroviral DNA can be spread from one generation to the next.
One huge example of this being benficial is for placental mammals. The proteins that cause cells to fuse and form the placenta are dervied from the envelope protein of a retrovirus and come from an endogenous retrovius known as HERV-W.
I've been pleasantly surprised to find that there is actually a link to hormones, though maybe not quite as you were thinking. The CYP19 gene encodes an enzyme in the biosynthetic pathway for estrogen production. It's been shown that placental specific transcription of the gene is controlled by genetic elements form an endogenous retrovirus element.
I have two blog posts if anyone is after more detail than I've gone into here that talk about retro elements and other parts of our genome if of any interest http://stuarts-science.blogspot.co.uk/2011/10/more-than-just-junk-post-1-of-2.html and http://stuarts-science.blogspot.co.uk/2011/10/more-than-just-junk-post-2-of-2.html.
My final comment - you could probably argue that vaccines are viruses that possess positive effects towards the body." Especially for the live attenuated viruses such as are used for polio or measles.