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Health 101 Topic 5 The Ecology of the Human Body and Health: Infectious Diseases (abstract) 1/ INFECTIOUS ORGANISMS Infectious organisms can be classified in a number of ways. In this course, I have chosen to classify them according to their size f

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Health Studies
HLTH 101
Glenn Ward

HLTH 101 Fall 2010 TOPIC 5: THE ECOLOGY OF THE HUMAN BODY AND HEALTH: INFECTIOUS DISEASES 1/ INFECTIOUS ORGANISMS Infectious organisms can be classified in a number of ways. In this course, I have chosen to classify them according to their size first, and then according to their taxonomic classification. i. Subcellular Organisms in fact, these are not technically organisms but are complex microscopic agents that usually (but not always) reside within living cells) well discuss two main types: viruses and prions VIRUSES exist basically as RNA or DNA molecules (generally not both) encased inside a coat of protein about 1500 viruses have been identified (so far), only a small number of which are believed to affect human health viruses have a simple existence outside host cells they are obligate intracellular parasites, which means that they must enter the host cell to reproduce all cells are susceptible to viral infection even single celled organisms such as bacteria can be infected with viruses (bacteriophages are viruses that infect bacteria) viral reproduction can damage the host cell when the virus reproduces, the offspring viruses can then invade a new cell and replicate, resulting in damage to the new cell, etc. HLTH 101 Fall 2010 because of the ability of the virus to travel through the body, there is a low association between the route of entry and the tissue most affected by the virus common diseases caused by viruses include: i. common colds ii. HIV (AIDS) iii.influenza iv. HPV (human papilloma virus) v. herpes vi. measles PRIONS prions are characterized as proteinacaous infectious particles they lack DNA and RNA and consist mainly of protein- like molecules they appear to exist in all brains their mechanism of action is still not well- understood, but research suggests that prions are susceptible to alterations in their shape or configuration if their configuration is altered, these altered prions can reproduce and propagate throughout nearby cells this eventually leads to the death of neural cells in which the prions reside altered prions can be transmitted through food and surgical instruments as infectious agents rare diseases caused by prions: i. transmissible spongiform encephalopathy ii. CJD (Cruetzfeldt-Jakob disease) iii.vCJD (form of CJD possibly associated with bovine HLTH 101 Fall 2010 spongiform encephalopathy [BSE] ii. Unicellular Organisms unicellular organisms are those that exist as single cells as such, they are more complex that viruses and prions, but are still relatively simple however, they are highly specialized for life in their respective environments the two types of cellular organisms associated with infectious disease are bacteria and protozoa BACTERIA bacteria are unicellular prokaryotic organisms structurally, they are highly adapted for survival 1) most (but not all) bacteria are enclosed in a capsule among other things, this capsule makes the bacteria resistant to phagocytosis the capsule also plays a role sometimes in the virulence of the bacteria 2) all bacterial cell walls contain peptidoglycan (note that some sources will refer the Archaebacteria as an exception to this rule. While the cell walls of Archaea do not contain peptidoglycan, it has become common over the past decade to refer to them as a prokaryote domain separate from bacteria. As they are not known at this time to contribute to human health problems, they will not be included in this discussion) this substance provides rigidity and resistance to lysis it also determines the gram positive and gram negative status of the bacterium (important for determining appropriate antibiotic treatment) 3) some bacteria contain cytoplasmic organelles called
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