Viruses in the Permafrost - A New Health Threat?

upload.wikimedia.org_wikipedia_commons_b_bf_megavirus.jpg A scientific study recently published in the journal Proceedings of the National Academy of Science (PNAS) details the discovery of a 30,000 year old virus in the thawing Siberian permafrost. Surprisingly, the authors of this study were able to bring the virus back to “life”, in the sense that they were able to restore it to an infectious state wherein it could replicate even though it had not done so in millennia. The discovered virus, known as a Pithovirus sibericum, is only able to infect single celled amoebae and as such it poses no risk to human health though. Even so this discovery raises concerns that the increasing trend towards global warming may have other unintended side effects beyond rising sea levels and crop failure. Is it possible that we may revive some ancient virus that is infectious to humans and that we as a species have long since lost our natural defenses to?

Viruses and You

upload.wikimedia.org_wikipedia_commons_thumb_9_90_permafrost_pattern.jpg_800px-permafrost_pattern.jpg The reason that the term “life” was in quotes above is that whether or not viruses are alive is a debatable subject that largely depends on how one defines what it is that constitutes being alive. Viruses are composed of their own genetic material, but they are intrinsically unable to reproduce without a host cell in which to do so. In a sense, one could think of viruses as little more than malevolent pieces of genetic material that at some point in our evolutionary history evolved a means to persist outside of the cells in which they were created, but even so they still must return to these cells to reproduce. This lack of autonomy makes it doubtful that viruses are truly alive in a strict sense of the word, and thus the notion that a virus has been revived from the Permafrost may be somewhat faulty. Even so, it is accurate to say that the virus was restored to an infectious state despite thousands of years of dormancy, and this feat is no less impressive than was reviving a virus anew.

When a virus invades a cell - for example, the influenza virus invading the cells of your respiratory tract - it takes over the normal machinery of these cells. Cells are normally protein producing machines, as proteins are essential for virtually all cellular functions and their production is of the utmost importance for both host cells and viruses. When a virus takes over protein production machinery in its target host cell, it tends to shut down or otherwise impair normal host protein translation, which will eventually have the potential to cause the cell to die and lead to disease related symptoms like a sore throat. In addition, in multicellular organisms this recognition of virus will lead to a coordinated immune response that has the potential to cause additional damage but that will, in the long run, eliminate the virus from the system. Pithovirus sibericum is only able to infect amoeba which are single celled organisms, and as such lack the complexities of the mammalian immune response.

Pithovirus sibericum

This newly discovered and restored virus is the member of a relatively new family of viruses that are gigantic as far as viruses go. Most virus particles are compact units of proteins and DNA that are almost impossible to visualize without extensive magnification via the use of electron microscopes. This newly discovered virus, on the other hand, is the size of a small bacteria and can be viewed with a regular high power light microscope. Despite its incredible size, the virus does not contain that many kinds of proteins. This means that the virus is mostly empty space, and it has several unique structural characteristics visible in the referenced reports, including a honeycombed cap structure on the end of the virus. It is able to reproduce itself in the cytoplasm of the amoeba that it invades, thereby producing many viral particle progeny. This newly revived virus was discovered when researchers applied samples from the Siberian permafrost to amoeba in the lab and looked for death of amoeba. From the dead amoeba, they were able to isolate this sample virus.

Demons in the Ice?

This resurrection of sorts inevitably begs the question - are we at risk from viruses or other organisms that might thaw out of the melting ice reserves around the world? Viruses are certainly the most likely organisms to be resurrected as they are fairly simple as far as organisms go, though the same research group has previously demonstrated their ability to resurrect 30,000 year old plants as well meaning that in the proper context man sorts of thawing are possible. It should not be overly surprising that viruses can be thawed from the ice if they were frozen in the proper conditions, as laboratories that study viruses will often maintain stocks of their virus of interest by freezing them at very low temperatures. As long as the freezing reaction happens fairly quickly and there is enough virus in the sample then the virus can be thawed out. Admittedly, it is somewhat surprising that the virus was fully intact as it is known that DNA tends to have a half life on the order of hundreds of years making it surprising that so much DNA could have survived for so long. Even so, it is clearly possible that such viruses can be resurrected.

The authors of the original study express concerns that the thawing of the tundra and other vestiges of the last ice age may reveal viruses that can infect humans and other important animals and that we are no longer prepared to fight as we as a species will not have seen those viruses in millennia. This would represent a heretofore unrecognized threat of global climate change that only compounds the significant danger it poses to the world as a whole. That being said, the odds of a pandemic virus thawing out of the snow is incredibly low. For one, the vast majority of frozen viral particles will be destroyed by ice and age rendering them incapable of replication in any form. Even for the viruses that do thaw out, they will be far more likely to infect amoeba or bacteria than larger organisms, as the majority of viruses in the world target single celled organisms. And even on the off chance that the viruses that thaw can infect humans, they are unlikely to be exceptionally pathogenic, Indeed, it is hypothesized that we live with billions of viral particles on a daily basis and our bodies do not suffer constant states of disease, confirming that the threat posed by thawed viral particles is quite low.

Conclusions

In summary, it has now been shown that viral particles trapped in ice for tens of thousands of years have the potential to be revived so that they can infect their preferred cell targets of choice. This resurrection is unique and is an important scientific breakthrough which may allow for the identification and study of viral lineages and viral lineages over time. There is a minute but not nonexistant chance that a thawed virus might be a threat to human life, and if this were to be the case it would have the potential to spread through the population relatively unchecked as we will likely have lost any immediate defenses to it do to a lack of selective pressure over the last 30,000 years. Even so, as the authors of the Nature summary of the original study point out, it is far more important that we focus on the more immediate concerns of global climate change - rising sea levels, and other temperature related changes to our immediate environment. The thawing of sinister viruses is a real possibility, but it is so remote that it is far more likely that society will be decimated by a newly discovered virus than by one that time has forgotten.

References


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