Hth245 - week of 9/19/2016
Hth245 - week of 9/19/2016 HTH 245
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This 7 page Class Notes was uploaded by Grace Notetaker on Saturday September 24, 2016. The Class Notes belongs to HTH 245 at James Madison University taught by Dayna Henry in Fall 2016. Since its upload, it has received 4 views. For similar materials see Foundations of Infectious Disease in Health Sciences at James Madison University.
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Date Created: 09/24/16
HTH245 – Week of 9/19/2016 – Chapters 5 and 6 Chapter 5 – Viruses and Prions Viruses as Infectious Agents o Pandemic = worldwide outbreak of disease Spanish Flu (1918) killed 50 million people worldwide in one year HIV/AIDS (latter 20th century) is currently devastating worldwide, particularly in Africa o Remember – viruses are subcellular Therefore, they can replicate only when gaining access to a host cell Host cell is taken prisoner and turned into a virus producing machine Obligate intracellular parasites o Since viruses are intracellular, they can be “tamed” and used as vehicles to deliver “good” genes to replace defective or non- existent ones = virotherapy o Virus = “poison”, “slime” Ivanowsky proved viruses are “filterable” (1892) Filtered extracts of tobacco leaves infected with tobacco mosaic disease through filters that were known to filter bacteria Injected extracts from the filter into healthy tobacco leaves and observed symptoms of the disease Showed the infectious agent was smaller than bacteria Now viruses can be viewed with an electron microscope o ALL CELLS ARE POTENTIAL HOSTS FOR VIRUSES Virus Structure o Second smallest microbe (prions = smallest) Bacteria can be seen with a light microscope, but viruses can only be seen with an electron microscope (bacteria = microscopic, viruses = subcellular) o Complete viral particale = virion o Nucleic Acids Have either RNA or DNA genomes, but not both Either single tailed or double tailed 4 types (slRNA, dlRNA, slDNA, dlDNA) o Protein Coat –capsid Nucleocapsid – nucleic acid genome plus the protein coat coat made of capsomeres 3 arrangements of capsomeres o helical series of rod-shaped capsomeres that form a continuous helical tube containing the nucleic acid o icosahedral 3-dimensional, 20-sided, triangular structures that confer geodesic- appearance i.e. spaceship earth @ epcot Disney world o complex polyhedral head, a helical tail, and tail fiber tail fiber – attach to host cell o Viral Envelope Some viruses, while emerging from host cell, acquire a piece of it’s plasma membrane - enveloped viruses 2 Envelopes modified by some of the membrane proteins being replaced by viral proteins o i.e. spikes – important for the attachment of viruses to host cell no envelope – naked/nonenveloped viruses Viral Classification o Superficially – classified by what type of organism the virus infects (plant, animal, or bacterial) o Clinically – according to the organ or organ system involved Dermotropic – skin Viscerotropic – internal organs Pnuemotropic – respiratory system *some viruses can infect more than one system o Biological – based on virus biology Nucleic acid content Capsid structure Number of capsomeres Viral Replication o Easiest to study bacteriophages because since viruses are obligate intracellular parasites and they need living host cells to survive i.e. T4 bacteriophage and E.coli 6 steps o absorption receptor molecules (on cell wall in bacteria, but cell memebrane in animals) – used by viruses to “dock need to “chance upon” the right receptor 3 recognition specificity = host range o penetration at this point, virus is on surface 4 ways of getting nucleic acid into cell: entry by endocytosis (virion inside cell is contained within a vesicle) entry by fusion w host cell membrane entry of only nucleic acid entry of nucleic acid after lysosome of bacteriophage degrades portion of the cell wall (note – animal cells have no cell wall) o replication uses host cell as a virus protein producing machine by expressing (transcribing and translating) nucleic acid contents o assembly o release 2 ways: lysis of bacterial host cell releasing hundreds of bacteriophages o kills host cell budding/extrusion: reverse endocytosis o creates nucleic envelope when leaving host cell by taking piece of host membrane o gradual and continuous 4 Host Cell Damage o Cytopathic effect = marks of cell deterioration cause by virus Can be used to identify many viral infections (specific virus, specific CPE) Examples o Cell shrinkage, detachment, cell lysis o Syncytia formation Giant multinuclear cells that are believed to move viruses around quicker (from cell to cell) i.e. HIV, measles o Negri bodies Present in brain tissue of animals with rabies (found 50% of the time) Use direct fluorescent antibody test (dFA) Cultivation of Viruses o Remember – viruses are intracellular obligate parasites (need living host cells) Bacteriophages: Bacteria cells are easy and inexpensive to culture so there are plenty of bacteria to use as hosts to culture bacteriophages Animal viruses: hindered, using live animals is expensive and unethical Embryonated (fertile) chicken eggs o Use several different sites within the egg that specifically support virus o i.e. manufacturing flu vaccine – influenza virus can be cultured in chicken eggs Cell culture o Virus cultured in petri dishes, flasks, etc. with a complex mixture of nutrients o Viral suspension put in culture flask 5 o Viral growth detected by microscope and CPE Diagnosis of Viral Infection o Rarely attempt to culture sample of people suffering a viral infection (like doctors do to diagnose bacterial infections) o Antibody molecules Molecules in the patient’s blood that are produced to fight specific antigens Presence in blood stream shows signs of current or past infection o Majority of viral infections can be identified with patient symptoms (better for common viral infections, killed by immune system) o Commercial test kits for some more acute viral infections (i.e. HIV, West Nile Virus) avoids transmission through blood transfusion Enzyme-linked immunosorbent assays (ELISAs) – detect viral antigens and antibodies o Extreme molecular testing used for viral encephalitis and meningitis – “spinal tap” sample, polymerase chain reaction (PCR) amplify nucleic acid Replaced brain biopsy Phage Therapy o Remember – bacterial viruses can wipe out bacterial infections (i.e. T4 phage attacking E. Coli); therefore… o We could use them to treat diseases o Replaced by antibiotics in 1940’s Remember – overuse of antibiotics is causing antibiotic resistance (refer to chap. 2 of Microbial Challenge) Antibiotic resistance has sparked interest in phage therapy Virotherapy o Remember – viruses are obligate intracellular parasites ( good at entering a cell); therefore, 6 o They make good “vehicles” or vectors Must target a certain type of cell Must deliver “good” genes o Can be used in cancer treatment Oncolytic (cancer-killing) viruses – destroy cancer cells kill through lysis (replicating inside tumor until it bursts) Biology of Prions o Proteinacious infectious particles o Smaller than viruses, with no DNA or RNA o 1957 – Kuru in Papua, New Guinea o prions = found in mammal brains o infectious prions = misfolded amino acids, highly stable (resist freezing, heating, pasteurization, etc.) PrP gene = prion protein o i.e. mad cow disease, transmissible spongiform encephalopathies To learn more and get OneNote, visit www.onenote.com. 7
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