DEVTOME.COM HOSTING COSTS HAVE BEGUN TO EXCEED 115$ MONTHLY. THE ADMINISTRATION IS NO LONGER ABLE TO HANDLE THE COST WITHOUT ASSISTANCE DUE TO THE RISING COST. THIS HAS BEEN OCCURRING FOR ALMOST A YEAR, BUT WE HAVE BEEN HANDLING IT FROM OUR OWN POCKETS. HOWEVER, WITH LITERALLY NO DONATIONS FOR THE PAST 2+ YEARS IT HAS DEPLETED THE BUDGET IN SHORT ORDER WITH THE INCREASE IN ACTIVITY ON THE SITE IN THE PAST 6 MONTHS. OUR CPU USAGE HAS BECOME TOO HIGH TO REMAIN ON A REASONABLE COSTING PLAN THAT WE COULD MAINTAIN. IF YOU WOULD LIKE TO SUPPORT THE DEVTOME PROJECT AND KEEP THE SITE UP/ALIVE PLEASE DONATE (EVEN IF ITS A SATOSHI) TO OUR DEVCOIN 1M4PCuMXvpWX6LHPkBEf3LJ2z1boZv4EQa OR OUR BTC WALLET 16eqEcqfw4zHUh2znvMcmRzGVwCn7CJLxR TO ALLOW US TO AFFORD THE HOSTING.

THE DEVCOIN AND DEVTOME PROJECTS ARE BOTH VERY IMPORTANT TO THE COMMUNITY. PLEASE CONTRIBUTE TO ITS FURTHER SUCCESS FOR ANOTHER 5 OR MORE YEARS!

Ebola Virus

If you have been following the news lately, then you have likely heard about the new outbreak of Ebola or an Ebola like disease in Guinea, a country which has in the past never had a confirmed case of this disease. The name Ebola conjures images of bleeding and death in the minds of anyone familiar with the term, but in general most people do not know much about it, as it is a disease that exists almost exclusively within Africa, and is thus easy to put out of sight and out of mind for many of us in the Western World. But what exactly is Ebola virus, and why is it that it has such a lethal reputation? This article aims to provide a run down of the specifics of Ebola, so that anyone can understand why these viruses are so dangerous, and why it is important that we study them in order to better understand them.

The Virus

Ebola is a viral disease caused by a virus of the Filovirus family, which was discovered fairly recently. In reality, there are a number of closely related Ebola viruses that likely differ slightly in their origins, and they all cause almost identical disease with some differences in lethality or other aspects of disease. These closely related viruses are not unusual and are in fact typical of most viral infections - for example, there are numerous strains of the influenza virus which may come from pigs or birds, and each year's influenza virus strain du jour has unique characteristics that distinguish it even though it is still the same group of viruses. As such, it is useful for scientists to track these individual groups of Ebola virus in order to understand the origins of the virus, but for the public it is most important to simply understand that Ebola is a dangerous virus that they need to avoid regardless of the strain.

Ebola was not widely known until the latter portion of the 20th century, but where did this deadly virus originate? It is likely that these Filoviruses have been around for millennia and that we simply failed to take notice of them prior to outbreaks of horrifying disease in the human population, but this means that the virus must have entered the human population from some external source. Indeed, this is how all viruses that cause novel outbreaks of disease in humans arise - they come to us from other species, in a process known as zoonotic infection. For Ebola, the source of this dangerous virus is thought to be bats that harbor large amounts of Ebola virus and related viruses. When humans interact with infected bats, then they risk catching the disease from these bats and spreading it to those around them. Even when there is not an active human Ebola outbreak, the disease is not gone - instead it simply persists in infected bats and possibly other species, waiting to be reintroduced into another susceptible host such as a human following a chance enounter.

If Ebola is so dangerous in humans, then why is it not equally dangerous to the bats in which it is thought to normally persist? The reason for this touches on some of the core tenants of understanding diseases on the whole, rather than simply Ebola virus. If a disease is very dangerous to its host, then it will often kill said host (as is the case for Ebola in humans), resulting in the virus not being able to transmit itself to many other hosts. Indeed, if an infected human is able to survive with Ebola infection for a long period of time then they would have the potential to transmit the disease to many more people than if they rapidly died. Accordingly, it is to the advantage of Ebola (or any virus or bacteria or parasite) to coexist with their host in such a way as to not prove lethal. While it is not fair to anthropomorphize these microscopic organisms, from an evolutionary perspective reproduction or replication are the most important aspects of life, and as such any advantage that allows a virus to replicate and spread to greater levels will be selected for evolutionarily. This tends to result in diseases that cause very minor infections in their normal hosts, potentially even proving to be completely asymptomatic. These species are known as disease reservoirs, as they harbor the virus or bacteria in question even when there isn't an ongoing outbreak of disease. Bats are thus a reservoir for Ebola, storing abundant virus that can eventually return to their local human populations to cause a deadly outbreak.

As an aside, humans are thought to be reservoirs from many viral and bacterial diseases which do not generally pose a threat to us, but which could be harmful if released into certain other susceptible species. We simply never notice these potential pathogens, because for us they are inconsequential and they are simply part of the complex microbial communities that all life forms naturally harbor. Thus, much as bats harbor Ebola and other strange diseases that can prove lethal to humans (for example, SARS, the corona virus that causes severe acute respiratory syndrome), humans have the potential to harbor other unique and potentially lethal diseases without ever noticing that they are present.

The Disease

Perhaps the reason that Ebola is so infamous is that it causes a horrific and highly lethal disease that captures the imagination with its cruelty. Ebola is a virus from a group of viruses known for causing hemorrhagic fevers - that is, they cause those infected with them to bleed profusely and develop a fever. These viruses are among the most dangerous viruses known in the world, and on the 1-4 scale of biosafety levels used by many research agencies throughout the world, Ebola and other hemorrhagic fevers rank at level 4, which is the deadliest biosafety level and is shared with the infamous Smallpox virus. These viruses are only approved for study at specialized research facilities in the US, Russia, France, and select other areas in the world and researchers need to wear full “moon suits” in order to avoid infecting themselves accidentally with these lethal agents.

In humans, Ebola is thought to primarily infect two types of cells - monocytes and endothelial cells. Monocytes are hardy cells of the immune system which are important for immune responses to disease and are white blood cells that are often important for the destruction of invading pathogens such as Ebola. Ebola virus is able to replicate within these abundant cells that exist in the human bloodstream, eventually leading to the virus being released into the bloodstream at high levels. Once in the bloodstream, Ebola is able to infect its other type of target cell - the endothelial cell. The endothelium is the cell layer that lines multiple tissues, mst importantly blood vessels. As Ebola thus begins to infect the walls of blood vessels, these cells begin to sustain extensive damage. This damage originates both from the virus itself, which can kill cells as it replicates (as viral replication compromises the normal functionality of the cell in which it is present), and from the immune system, which recognizes that a cell is infected with virus and generally tries to kill that cell in order to prevent it from producing more viral particles that can infect more cells. These dual sources of inflammatory damage associated with Ebola infection result in the extensive death of endothelial cells, compromising the normal barrier between the bloodstream and the rest of the body, leading to blood leakage - a hemorrhage.

It is the hemmorhagic nature of Ebola that makes it so lethal - massive blood loss can often lead to the death of those infected, and indeed about 70% of known Ebola cases are believed to be lethal, with some differences between strains of the virus. In addition to lethal hemorrhage, the virus causes a high fever and other influenza like symptoms which result from extensive disseminated inflammation. These inflammatory responses are the body's reaction to the viral infection, and can lead to disseminated blood clotting and pain, potentially resulting in the failure of major organs. Between organ failure and blood loss due to endothelial cell death, it is not surprising that Ebola is such a lethal virus.

Once again, bats clearly do not experience this lethal hemorrhage that defines this disease in humans, so how is it that our endothelial cells are so vulnerable whereas those of bats are not? The reason is simple - as discussed earlier, the virus likely evolved to be able to replicate in bats without killing them, while it did not encounter humans until long after undergoing said evolution. Similarly, the virus can infect monkeys or pigs, although it can cause disease in these more susceptible hosts making this a closer corollary to the human model of disease. It is likely that Ebola does not infect endothelial cells in bats and that it is just unfortunate coincidence that it does so in humans. Alternatively, it may be that the endothelial cells of bats simply have special adaptations that allow them to tolerate Ebola infection without cell death, thus preventing hemorrhage from occuring.

Viral Control

While Ebola is an extremely lethal disease, it is still fairly rare which is fortunate given its high case rate lethality. The reason for this is that Ebola does nto spread easily between humans as it may between bats. To catch Ebola, a person needs to come into close contact with the fluids of someone who is actively suffering from an infection, and blood is often the most common source of infection. For this reason, Ebola is usually only directly spread to the close friends and family of infected individuals who care for them during their illness. Due to its low rate of spread, Ebola is generally restricted to areas where its reservoir species persist - Sub Saharan Africa. Occasionally cases of Ebola will arise in other parts of the world as a result of people visiting areas experiencing an outbreak, however it is generally easy to quarantine infected individuals and thus prevent the virus from being spread further. Without a local reservoir species, the virus then simply burns out and does not spread, as is the case with a recent case of Ebola like illness in a Canadian man that had recently visited Liberia.

Despite its monstrous nature, there is no treatment for Ebola infection. Infected individuals are generally given supportive care such as anti-inflammatory drugs, pain kilers, and blood transfusions as needed. Ultimately, however, it is up to their own immune system to over come this deadly pathogen. There are some antiviral drugs which may help against certain related hemorrhagic fevers, however these drugs have proven to be completely ineffective against Ebola and as such it is essential that scientists work to research new Ebola cures. As mentioned above, Ebola can only be researched in specific institutions due to the danger associated with it. Fortunately, scientists are able to study certain aspects of Ebola without using the whole virus, but studying certain aspects of the viral life cycle such as viral entry into endothelial cells without the risk of viral replication in these cells. It is this type of research that has the greatest potential to provide new insights into how Ebola works and how we can defeat it.

Until science is able to find a way to defeat Ebola with a vaccine or an antiviral drug treatment, it is up to public health officials to contain outbreaks before they spread into an epidemic form. In areas where Ebola infections are believed to arise, there are generally quarantine efforts and public health campaigns that aim to prevent people from touching infected people or their blood. These programs are thought to be helpful in curbing rates of infection, but they cannot offer help to those already infected, nor can they prevent all new cases from arising. In Guinea a recent law was passed to ban the eating of bats, in order to try to prevent people from catching Ebola like disease from these reservoir species. These public health efforts are currently our best defense against pandemic hemorrhagic fevers, and hopefully in time science will be able to identify more reliable means of curbing these potentially deadly infections for good.

References

  • 1. Chandran, K., et al., Endosomal proteolysis of the Ebola virus glycoprotein is necessary for infection. Science, 2005. 308(5728): p. 1643-1645.
  • 2. Drosten, C., et al., Rapid detection and quantification of RNA of Ebola and Marburg viruses, Lassa virus, Crimean-Congo hemorrhagic fever virus, Rift Valley fever virus, dengue virus, and yellow fever virus by real-time reverse transcription-PCR. Journal of clinical microbiology, 2002. 40(7): p. 2323-2330.
  • 3. Jaax, N.K., et al., Lethal experimental infection of rhesus monkeys with Ebola-Zaire (Mayinga) virus by the oral and conjunctival route of exposure. Archives of pathology & laboratory medicine, 1996. 120(2): p. 140-155.
  • 4. Jahrling, P., et al., Preliminary report: isolation of Ebola virus from monkeys imported to USA. The Lancet, 1990. 335(8688): p. 502-505.
  • 5. Le Guenno, B., et al., Isolation and partial characterisation of a new strain of Ebola virus. The Lancet, 1995. 345(8960): p. 1271-1274.
  • 6. Leroy, E.M., et al., Fruit bats as reservoirs of Ebola virus. Nature, 2005. 438(7068): p. 575-576.
  • 7. Sanchez, A., et al., Sequence analysis of the Ebola virus genome: organization, genetic elements, and comparison with the genome of Marburg virus. Virus research, 1993. 29(3): p. 215-240.
  • 8. Sullivan, N.J., et al., Development of a preventive vaccine for Ebola virus infection in primates. Nature, 2000. 408(6812): p. 605-609.
  • 9. Volchkov, V.E., et al., Processing of the Ebola virus glycoprotein by the proprotein convertase furin. Proceedings of the National Academy of Sciences, 1998. 95(10): p. 5762-5767.
  • 10. Wool-Lewis, R.J. and P. Bates, Characterization of Ebola virus entry by using pseudotyped viruses: identification of receptor-deficient cell lines. Journal of virology, 1998. 72(4): p. 3155-3160.
  • 11. Yang, Z.-y., et al., Distinct cellular interactions of secreted and transmembrane Ebola virus glycoproteins. Science, 1998. 279(5353): p. 1034-1037.

Science | Health


QR Code
QR Code ebola_virus (generated for current page)
 

Advertise with Anonymous Ads