Study Guide

Microorganisms: Viruses In the Real World

  • Pop Culture

    With all the zombie movies that have come out in the past few years, one of the underlying causes of zombification is a virus. So far, we don't know of any viruses that actually make people zombies; however, many of the viruses mentioned in zombie movies are related to real viruses. Rabies virus infects individuals and causes manic aggressive behavior, including biting individuals, which increases the likelihood of the virus spreading to another host.

    The "rage" virus mentioned in 28 Days Later exhibits properties similar to rabies virus. In I Am Legend, a mutant version of measles virus causes people to become zombies, which would be unlikely as measles virus is spread through the air, and generally does not infect the brain (which is what would make a virus zombie-inducing, presumably). The movie Zombieland claims that a variant of the prion mad cow disease is responsible for causing zombification. This is far more plausible than the I Am Legend virus, as prion disease is spread through consuming brain tissue. So, if the disease were to somehow cause individuals to desire brain tissue, then they could become zombies.

    The movie Contagion also talks about how an epidemic flu-like disease would spread throughout the human population. It discusses issues of control of virus spread, including quarantine, how viruses can recombine between species (the virus in the movie is a combination of a pig and a bat virus that can infect humans). Ironically, the virus in this movie is also a paramyxovirus (like measles virus), but it also infects the brain. Either the people behind Contagion are trying to validate the possibility of the I Am Legend virus existing, or they just want to do as well in the box office as I Am Legend. We think they should just shoot for Ratatouille.

  • History

    The word virus was first used to describe an agent that causes infectious disease by Edward Jenner...you know, the small pox guy. The first person to identify a virus as distinct from bacteria and other cellular life was probably Dmitri Ivanoski, who filtered tobacco extracts that had tobacco mosaic disease—caused by tobacco mosaic virus—and found that he could spread disease through these filtered extracts. Martinus Beijerinck did Dmitri one better by passaging the filtered extract again and again, proving that the filtered extract was actually growing and replicating in each plant. It was not simply a toxin.


    Chicken Sarcoma (must…tear…chicken...apart)

    In 1911, Peyton Rous discovered that a virus caused cancer in chickens, or a chicken sarcoma, and he was the first to show that viruses caused cancer. The virus he discovered, Rous sarcoma virus, was a retrovirus.

    Since the discovery of viruses as infectious, disease-causing agents, they have been a useful tool to understand the biology of bacteria and eukaryotic cells. Because viruses need to hijack the host cell, they can be used to understand the functions of certain proteins in a cell. The following discoveries originated from virus research.

    • The first crystallization of protein was of tobacco mosaic virus.
    • The discovery of reverse transcriptase led to understanding of RNA expression in various cells.
    • The discovery of oncogenes through retrovirology.
    • The Phi X 174 bacteriophage became the first sequenced genome.
    • The first attempts at gene therapy were developed using retroviruses.

    Therefore, virus research is not only important to understanding how viruses infect us, but it is also important for getting at our own biology through its disruption during a virus infection.

  • Research

    The development of PCR techniques has considerably improved our ability to do virus research. One of the major advantages of new PCR techniques includes deep sequencing techniques, which allows scientists to identify DNA sequences from the oceans, or other remote locations. Because there is no need to culture cells or grow viruses, they can just simply randomly sample areas and just determine the sequences found in that area. So, if there are a lot of viruses, then you can identify virus sequences in that area.

    Research identifying ocean viruses has led to some interesting gene discoveries. Viruses that have unique polymerase genes that are DNA-dependent DNA polymerases, similar to pox viruses, but belonging to their own group have been identified in the ocean. Viruses such as the mimivirus, a very large unique group of viruses found in the ocean are very large viruses. Mimiviruses infect ocean amoebas, and have diameters of approximately 400 nm in length (twice that of poxviruses), and has a 1 megabase long genome sequence.

    Mimiviruses are larger than many very small bacterial genomes, and it is highly likely that through more deep sequencing we will also identify many viruses that are more like cellular life than the viruses we already know. This raises the question again on whether viruses are indeed living organisms, and perhaps we should revise the 3 domain architecture of life to create another level of organization to include viruses in the tree of life, to separate between ribosomal based life (cellular life), and non-ribosomal life (viruses).

    While PCR techniques have dramatically improved our ability to detect virus sequences in the environment, this has also led to the detection of false positives. Many researchers have been looking for a virus origin of many chronic diseases that we don't understand, such as chronic fatigue syndrome. Recently, a group published a report saying that they identified a retrovirus called XMRV, which was found in the blood of patients with chronic fatigue syndrome, but not in normal healthy individuals.

    While this provided a lot of hope for individuals diagnosed with this disease, it turned out that XMRV was not in fact found in the blood of these patients, and the XMRV sequences that they found were in fact contamination from mouse DNA. So, many people were taking antiretroviral drugs in the hope of treating their illness, only to discover that there was no viral origin for their disease. These types of mistakes have become more prevalent with the ease of PCR techniques to identify viral sequences. Misguided research on identifying virus causes for tumors has led to what many skeptics calling ironically "rumor" virology*, a pun on tumor virology, implying that much of this research is wrong.

    *Unfortunately, we at Shmoop cannot fire the writer who came up with "rumor" virology. But boy would we like to.