Week 4 notes
Week 4 notes HTH 245
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This 5 page Class Notes was uploaded by Katlyn Palka on Sunday September 25, 2016. The Class Notes belongs to HTH 245 at James Madison University taught by in Fall 2016. Since its upload, it has received 2 views. For similar materials see Foundations of Infectious Disease in Health Sciences at James Madison University.
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Date Created: 09/25/16
Chapter 5: Viruses and Prions ● Viruses as Infectious Agents ○ They are obligate intracellular parasites: they must gain access into cells (host) in order to replicate ■ They can be genetically engineered to deliver good gene viruses into cells to replace defective or nonexistent genes (Virotherapy) ● Virotherapy is used to help treat cancer ○ They have either DNA or RNA but never both ○ They are subcellular ○ They can infect all cell types (microbes, plants, and animals) ■ All cells are potential hosts for viruses ○ Examples of viral infectious diseases ■ Smallpox ● The only disease that has been eradicated ○ The only place it exists is in governmental laboratories ● Edward Jenner developed a vaccine for it in 1796 ● Was used in biowarfare ■ Poliomyelitis ■ Spanish Flu ● Was a pandemic, that is an animal virus ● A strain of the flu that killed over 30 million people worldwide in one year ● It causes damage to the lining of the lungs allowing for fluid and liquids to enter the lungs. People infected drown in their own fluids ● It affected young, healthy people more than older, less healthy people ■ HIV/AIDS ● First recognized in the US in 1980s ● Now a worldwide pandemic that has devastated Africa ● Virus Structure ○ Viruses are the second smallest microbe (prions are the smallest) ○ They are simple in structure and may only consist of a nucleic acid wrapped in a protein coat ■ The complete viral particle with the nucleic acid and the protein is called a virion ○ Nucleic Acids ■ Either RNA or DNA (not both) ■ There are 4 categories of viruses ● dsDNA (double strand DNA) ○ Ex. chickenpox, smallpox, human papillomavirus, EpsteinBarr virus ● ssDNA (single strand DNA) ○ Ex. Parvovirus B19 (possibly slappedcheek disease) ● dsRNA (double strand RNA) ○ Ex. Hepatitis A virus, polio virus, norovirus, rubella virus, Ebola virus, influenza virus, West Nile encephalitis virus ● ssRNA (single strand RNA) ○ Ex. Rotavirus, Colorado tick fever virus, reovirus ○ Protein Coat ■ The protein coat is called the capsid which is made up of protein units called capsomeres ● There are 3 capsid types (based on their shape) that make up a viron ○ Helical ■ A series of rodshaped capsomeres ■ They form a continuous helical tube which contains the nucleic acid ○ Polyhedral ■ The capsomeres form icosahedrons which are 3D triangular structures that look like the epcot center at Disney ○ Complex ■ They have a polyhedral head, a helical tail, and tail fibers that are used for attachment to the host cell ● T hey look like a little spaceship ■ Nucleocapsid: refers to the capsid (protein coat) and the nucleic acid genome ○ Viral Envelopes ■ Nonenveloped: they have a protein surface ■ Enveloped: they have a plasma membrane that they stole from the host cell either on the way in or on the way out ● They contain the host and viral protein ● Some have spikes (a viral protein on the surface that aids in attachment of the viral cell to a host cell) ● Classification of viruses ○ Can be classified by their structure ■ Their type of nucleic acid or shape ○ Can be classified by the type of host cell that they like to infect ■ Microbe, plant, or animal ○ Can be classified by the organ or organ system that they infect ● Viral Replication ○ 5 stages ■ Absorption (attachment) ● The virus docks with the host cell surface receptors ○ They can only dock with the correct receptors ■ Penetration ● The viruses can get into the cell in 4 different ways ○ 1. Gets absorbed (endocytosis) ■ This entry way is for enveloped cells and when it enters the cell it bursts inside the cell and releases the virus ○ 2. Fusion: it attaches itself to the cell wall and spits out its genetic material ■ This happens with mumps and measles ○ 3. The viral cell sits on the outside of the cell wall (does not attach) and releases its genetic material ■ This is the way polio is infected in the body ○ 4. Sits on the outside of the cell and sticks a needle through the cell wall and injects its genetic material (the complex virus cells) ■ This one is only for when a virus infects a bacterial cell ■ Replication ● The process is dependent on the genome type of the virus ○ ssDNA, dsDNA, ssRNA, dsRNA ● The viral parts (protein and nucleic acid) are manufactured through the molecules of the host cell ■ Assembly ● Once the viral parts are made they assemble themselves to make new virions ■ Release (exit) ● The new virions are released in one of two ways ○ 1. They kill the cell and explode the cell ■ The virions that have envelopes ○ 2. The host cell is not killed and the new virions are released gradually (budding= the opposite of endocytosis) ■ When the virions are released they take the cell membrane with them and use it as an envelope to protect itself ● Host cell damage ○ Most viruses damage or kill the cell ■ CPE (cytopathic effect) is a characteristic of damaged cells from a virus ● This can help determine and diagnose what the virus is ● The growth of viruses needs to happen in living cells because they are obligate intracellular parasites ○ They grow the flu vaccine in embryonated chicken eggs ● Most viral infections are diagnosed based on signs and symptoms ○ Another way to diagnose a viral infection is through ELISAs (enzymelinked immunosorbent assays) ■ Look at if an antibody attaches to a specific antigen ● Phage therapy ○ Used when there is antibiotic resistance ○ They inject a virus to kill off bacterial infections ● Virotherapy ○ Genetically engineered viruses that are injected into the body ■ They attach to certain cells and leave others alone ■ Process: cells are removed, cultured, incubated with the virus, and then transplanted back into the body ● Prions ○ Smaller than viruses ○ No RNA or DNA ○ They are misfolded proteins ■ They attach to normal proteins and misfold them ■ The most deadly infectious disease ● 100% mortality rate Guest Speaker Bacterial Genetics