Interesting biological factoid of the day

Tiltsta

Show me your frittatas
Staff member
The vast majority of biological mass on the planet Earth is not from trees, or people, or even bacteria, it is virus particles. Scientist currently estimate there are approximately 10^31 (10 with 31 zeros) virus particles on Earth right now. This is more than the number of grains of sand on Earth. This accounts for 130-150 gigatons of carbon turnover in a year, which is about 5 times the amount of all other organisms on Earth combined. Viruses, with a few exceptions, are tiny and not visible even in a laboratory light microscope. If you were to line up 10^31 virus particles end to end, the chain of viruses would be long enough to reach from the Earth to the center of the Milky Way Galaxy and back to Earth. :messedup:
 
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and they will eventually be the only inhabitants of this earth.....

Well, a virus without a host is an inert biological entity, so most viruses have evolved to tune their replication rate to never eliminate all of their hosts. Some are even beneficial to their target organisms. Even the most pathogenic viruses select for escape mutant hosts that cannot carry productive infections. Anyway, the evolutionary clock has been ticking for billions of years, and the viruses haven't won out yet, so I think we are safe. You post does raise some interesting philosophical questions....most notably, at what point does a virus kill enough of the host that the virus is lost, and what in nature would select for such an event. Most virologists, myself included, would argue that the most successful viruses are those that do not cause significant disease (either for an individual, or for the population). Anyway, your point is a 'head scratcher' for science.
 
Tiltsta, how much do you know about oncolytic viruses and their effectiveness? And specifically w/r/t the brain? :tongue:
 
^^ Not my area, specifically, but I do work on viruses and their ability to cause cancer, and how they can control whether cells live and develop into tumors or ultimately die in some virus infections. Anyway, oncolytic viruses are very real, and a number of targeted herpes viruses have been developed (and are in early/mid clinical trials) to treat glioblastomas (there are other cancer oncolytics for other cancers as well). AAV is also in the works, but less advanced, as are other viruses. Some are directly lytic to tumor cells, and some alter the ability of tumors to resist conventional chemotherapy. So far, the data look very promising, but, the nature of intentionally delivering viruses to the brain as therapy is a major regulatory hurdle for regulatory agencies. One has to demonstrate a very low risk of potential inflammatory response (and for some viruses, transformation/cancer induction) in the brain, and this is likely to slow down the application of the technology to actual 'main stream' patients. In general, virus infections that make it to the brain are not good, and clinically present with seizures, paralysis, fever, encephalitis, and so on. The challenge is eliminating the negative effects of infection in the brain, leaving only the positive therapeutic benefit. In any event, from reading the papers, the data out there from trials look very, very promising, and for some people this is an 'only hope' type therapy, so to me the potential risk is better than doing nothing. If I had a lethal brain cancer, I would be in a trial group to get the therapy. A lot of negative aspects have been eliminated through considerable effort, but, how effective these efforts have been really require a large scale clinical trial. I suspect this will be a standard therapy in a decade or two, but for now it is still full of unknowns. Bottom line, everyone is a little gun shy from a regulatory standpoint from the attempts at using adenovirus to treat cystic fibrosis that was a failure that resulted in the death of a test subject. I think we have advanced a lot since then, but we are not ready yet.
 
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^^ Not my area, specifically, but I do work on viruses and their ability to cause cancer, and how they can control whether cells live and develop into tumors or ultimately die in some virus infections. Anyway, oncolytic viruses are very real, and a number of targeted herpes viruses have been developed (and are in early clinical trials) to treat glioblastomas (there are other cancer oncolytics for other cancers as well). Some are directly lytic to tumor cells, and some alter the ability of tumors to resist conventional chemotherapy. So far, the data look very promising, but, the nature of intentionally delivering viruses to the brain as therapy is a major regulatory hurdle for regulatory agencies. One has to demonstrate a very low risk of potential inflammatory response (and for some viruses, transformation/cancer induction) in the brain, and this is likely to slow down the application of the technology to actual 'main stream' patients. In any event, from reading the papers, the data look very, very promising, and for some people this is an 'only hope' type therapy, so to me the potential risk is better than doing nothing. I suspect this will be a standard therapy in a decade or two, but for now it is still full of unknowns. Bottom line, everyone is a little gun shy from a regulatory standpoint from the attempts at using adenovirus to treat cystic fibrosis that was a failure that resulted in the death of a test subject. I think we have advanced a lot since then, but we are not ready yet.
Thats pretty cool...I didn't realize they were looking at treating people this way.
 
Thats pretty cool...I didn't realize they were looking at treating people this way.

In Russia they treat a number of dangerous bacterial infections with viruses that infect and kill bacteria. Mostly this is for bacteria that are multi drug resistant or difficult to treat with antibiotics. Anyway, they have had sufficient success that this is used in a hospital setting in extreme cases, and is far beyond the area of 'research' therapy. The US has a number of labs and companies looking into the potential of applying this concept here. It is not without issues, as the death of the bacteria from infection can cause a massive immune response (killed bacteria release lots of things that activate the immune response), but the clinical data from the Russians looks really impressive. I suspect this will be a therapy for things like deep tissue bacterial infections in the next decade (the so called 'flesh eating' bacteria). This is much easier than treating human cells in a tumor and not killing non-tumor cells.
 
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The big problem with the brain targeted oncolytics has been targeting the brain (which is outside of normal blood circulation) and the fact that few viruses go to the brain due to the relative lack of actively dividing cells. In some ways the latter point makes targeting tumors versus normal brain easier, but getting the viruses to the target organ isn't so easy in therapeutic sense.

The big advances of the last decade is recognizing that even if a virus doesn't directly kill a tumor cell, the activation of the host immune system can lead to significant killing of cancer cells. The balance, as I mentioned, is balancing the level of immune response to kill tumors without to much bystander cell damage. The amazing advances in understanding the innate immune system in the last decade has helped immensely in this regard, but there is still a way to go.
 
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I need to read up on the blood brain barrier. Have heard about it but don't know anything about it. :embarrassed:
 
i guess my question would be.....once the viruses have targeted and eliminated the bacteria they were sent after....what do they do then.....do they die off, or do they look for something else to feed on???
 
Well, a virus without a host is an inert biological entity, so most viruses have evolved to tune their replication rate to never eliminate all of their hosts. Some are even beneficial to their target organisms. Even the most pathogenic viruses select for escape mutant hosts that cannot carry productive infections. Anyway, the evolutionary clock has been ticking for billions of years, and the viruses haven't won out yet, so I think we are safe. You post does raise some interesting philosophical questions....most notably, at what point does a virus kill enough of the host that the virus is lost, and what in nature would select for such an event. Most virologists, myself included, would argue that the most successful viruses are those that do not cause significant disease (either for an individual, or for the population). Anyway, your point is a 'head scratcher' for science.

"to never eliminate the host...." explain Ebola.
 
i guess my question would be.....once the viruses have targeted and eliminated the bacteria they were sent after....what do they do then.....do they die off, or do they look for something else to feed on???

Bacterial viruses don't infect human cells, as we are SO different from bacteria that the host cell machinery the bacterial viruses use just don't exist in human cells. The evolutionary space of viruses is insufficiently dynamic to have a bacterial virus adapt to human cells in any reasonable time frame. I would guess it would take millions of years of positive selection to see that happen...maybe longer. The bacterial viruses left over are simply picked up by the human immune response and eliminated.
 
"to never eliminate the host...." explain Ebola.

Ebola is a zoonotic infection, which leads to extreme pathogenesis in the recipient host (humans), while this is not likely the response in the native host. Not all people who get Ebola die. The lethality of Ebola is primarily due to the poor medical infrastructure (and cultural norms of families taking care of the sick in hospitals and funeral environments) in the areas of Africa where primary transmissions occur. In short, it is a virus with the worst route of transmission in the worst possible locale, but I don't expect it will ever be a global mass killer. Watch how fast it spreads in the US in an environment with a good understanding of barrier procedures and such. I counter your point with something like adeno associated virus, which causes no known disease, yet has a massive global prevalence. The best viruses don't cause disease. The ones we know about do, as no one looks for the virus that doesn't cause disease.
 
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