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Viruses, viroids, and prions

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Seth D. Greenlaw Biology101 Paper 1 June 8, 2002 Viruses, viroids, and prions are not technically living organisms. In this paper I will attempt to describe what makes them different from living organisms, why they are important, and what diseases they cause. However, before starting off on this whirlwind of biological information, it's important to define what viruses, viroids, and prions are. For example, Columbia University's Columbia Electronic Encyclopedia states, "A virus is a parasite with a noncellular structure composed mainly of nucleic acid within a protein coat" [1]. According to the Columbia Electronic Encyclopedia, "A viroid is an microscopic infectious agent, much smaller than a virus, that infects higher plants such as potatoes, tomatoes, chrysanthemums, and cucumbers, causing stunted or distorted growth and sometimes death. Viroids are single strands of RNA and lack the protein coat of viruses" [1]. The Columbia Electronic Encyclopedia continues to explain a prion as an "Undefined infectious agent thought to cause a group of diseases known as prion diseases or transmissible spongiform encephalopathies" [1]. Infectious and parasite are the two words that most accurately describe all three of these organisms. ...read more.


It's important to know that viruses can infect humans, animals, and plants in horrific proportions. However, I will only be focusing on viruses that are found in humans. For example, a retrovirus (HIV) is thought to cause AIDS, several viruses (e.g. Epstein-Barr virus, human papillomavirus) cause particular forms of cancer in humans, and many have been shown to cause tumors in animal. Other viruses that infect humans cause measles, mumps, smallpox, yellow fever, rabies, poliomyelitis, influenza, and the common cold [1]. Viruses through out history have devastated the human race as a whole. While HIV/AIDS grab the headlines these days back in 1918 the "flu" caused a global epidemic, or pandemic, that caused over 20 million deaths worldwide and 500,000 deaths in the United States [8]. Viroids, however, don't cause disease in humans (with the exception of Hepatitis D) while instead they are a common plant pathogen that can cause serious economic problems. For example, in a report from Mr. Hanold to the Australian Quarantine Committee in 1996, one can easily see the economic applications of such pathogens. ...read more.


This is a degenerative, transmissible and fatal neurological disease occurring in cattle. It affects the brain and the spinal cord. The disease is ultimately fatal for cattle within weeks to months after the symptoms become visible. This disease alone has had huge economic repercussions, as according to the London Observer Service, BSE "has cost Britain $6.4 billion, claimed the lives of 43 people and triggered fears that the death toll could eventually reach several million." [7]. Quarantine and vaccinations have provided some help in combating the seemingly unbeatable army of viruses, viroids, and prions. However, medical science and human determination can only do so much in this war against mutable enemies. Just as a meteor brought the ice age for the dinosaurs, perhaps the next cataclysm will not be from a meteor but tiny organisms that will bring a new type of "ice age" for us. When will the next epidemic, outbreak, or pandemic occur and will we be able to survive? These are questions that must be left unanswered as the future is an unforeseeable place and yet one must be reminded that life seems to have an unstoppable desire to survive. ...read more.

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