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VIRUSES CHAPTER 10
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What are Viruses? Obligate intracellular parasites Viral components
Nucleic acids Capsid Envelope
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Viral Shapes and Sizes Helical Polyhedral Spherical (Enveloped)
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Infectious Properties
Viral Host range From 1 species (polio virus) to many (Influenza virus) Viral specificity From 1 cell type (Hepatitis B virus) to several (CMV in GIT, lungs, spleen) Viral Origins ? Co-evolution with cells ? Degeneration
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Virus Classification 108 families so far Classification based upon
Pathogens for all life forms Classification based upon Nucleic acid type Single strand vs. double strand chromosome + versus – single strand Enveloped versus “naked"
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11 RNA Virus Families + strand RNA virus Family Picornaviridae
RNA dependent RNA polymerase makes a - strand intermediate template 3 Genera: Enterovirus Includes poliovirus, Hepatovirus Includes Hepatitis A Rhinovirus Attach to molecules of nasal mucous membranes, cause some colds
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Unique RNA Virus Cycle 2 + strands Retroviridae
Reverse transcriptase unique enzyme RNA to DNA Provirus synthesis Provirus integrates into host DNA No removal Activation and transcription later produces more viruses Includes HIV
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Antisense Virus Rhabdoviridae
RNA dependent RNA polymerase makes a Sense strand (+) for mRNA Antisense (-) strand as chromosome Includes rabies virus
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ds RNA Chromosome Reoviridae Non-enveloped
Cause respiratory and intestinal infections in adults Severe diarrhea in infants caused by Rotavirus Animals may be affected by some members
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ds DNA Virus Families Adenoviridae Cause many “colds”
Highly stable over pH and temperature changes 10-30% of infant diarrhea Infection may be associated with a rash
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ds DNA Viruses (cont.) Herpesviridae > 100 species Latent viruses
Herpes simplex virus Varicella virus Epstein Barr virus
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ds DNA Viruses (cont.) Papovaviridae Cause skin and genital warts
DNA may not be integrated into the host chromosome 13 papilloma viruses are associated with cervical cancer GardasilTM
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ss DNA Viruses Parvoviridae ss DNA viruses
Unrelated viruses or host genes needed to allow replication Human disease known as 5th disease (Erythrovirus) Canine Parvovirus gastroenteritis Dependovirus genus must coinfect with Adenovirus or Herpesvirus for replication, no human diseases
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Emerging Viral Diseases
Considerations: Reservoirs in animal populations Vectors Mutation/Recombination frequencies Immunity vs. containment (after rapid air travel of incubating patients)
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Viral Replication General Characteristics of Replication Adsorption
Penetration (virus or chromosome) Synthesis Maturation Release
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Lytic Bacteriophages Virulent T-even bacteriophages
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Bacteriophage growth Plaque Assay Virion
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DNA Animal Viruses Chromosome replication in host cell nucleus
Cytoplasmic ribosomes for viral mRNA translation Viral capsid proteins must return to nucleus for maturation phase Envelope proteins to plasma membrane
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RNA Animal Viruses Use RNA-dependent RNA polymerase
Cytoplasmic chromosomal replication and protein synthesis + strands always needed for mRNA Chromosome may be + strand or – strand, depends on virus family
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Retrovirus Cycle Use RNA-dependent DNA polymerase (Reverse transcriptase) + strand chromosome acts as template for ds DNA provirus Later transcription of provirus allows for virus production
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Early Virus Culture Methods
Live animals Research Eggs Vaccines Allergies
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Cell Cultures for Viral Growth
Primary – harvested animals cells Continuous – cancer or immortalized cells
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Viral Cytopathic Effects
Cytopathy Cell shape/size Cell adhesions (contact inhibition) Transformation (cells divide forever) Teratogenic effects CMV, HSV-1, Rubella TORCH series (Toxoplasma, Others like Chicken pox and Hepatitis B, Rubella, CMV, HSV
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Viruses and Cancer Cancer - Triggering of rapid uncontrolled cell division Mechanisms of cancer causation Block of tumor suppression genes Proto-oncogene activation Oncogenes (may be carried by DNA cancer viruses)
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