chapter 13

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    Describe this figure
    • Model of viral infection w/ varicella-zoster (chicken pox)
    • The infection is initiated either in the conjunctiva of the eye or in the mucosa of the upper respiratory tract
    • moves quickly to regional lymph nodes, where it can infect T cells
    • 4 to 6 days later, infected T cells move into the blood causing a primary viremia.
    • It moves to the liver, spleen and other organs, causing a second round of infection and then back into the blood causing secondary viremia (skin lesions appear)
    • moves into sensory ganglia in the peripheral nervous system, where it becomes latent
  2. What is an acute infection?
    • Best understood infections and involve the rapid production of viron's followed by rapid resolution and elimination of the infection by host defenses
    • Some are asymptomatic
    • main problem is the incubation period; by the time they show symptoms the virus has already been transmitted. two examples: common cold and influenza.
  3. What is a latent infection?
    • Is known as a persistent infection (chronic infection is also persistent)
    • caused when host defenses are either modulated or completely bypassed
    • virions are produced for months or even years
    • Cytotoxic T cells (CD8+) are key in getting rid of these infections (adaptive immune response).
    • no large scale production of virions
    • reduced or absent immune response
    • persistence of an intact viral genome so infections can reoccur
    • can be re-actived years after entry into host
  4. Explain slow infections
    • Lethal- associated usually w/ brain infections
    • Signs may not be seen until years after the primary infection
    • Once S/S appears (difficulties w/ brain function and motor skills), death usually follows very quickly
  5. What is antigenic drift?
    • Minor
    • Involves small changes in viron structure Results from mutations
    • Occurs after infection has began
  6. What is antigenic shift?
    • Major changes in viron structure
    • due to acquisition of new genes
    • this through co-infection or recombination
  7. Define virulent
    viruses cause significant disease
  8. Define non-virulent, attenuated
    At one point it was virulent, but now its not. They cause little or no disease.
  9. What are the three types of vaccines?
    • Live attenuated vaccine: made of intact virions rendered non-infectious
    • Inactivated or killed vaccine: composed of killed or dead virions
    • Subunit vaccine: composed of immunogenic parts of virions
  10. What are passive and active immunization?
    • Passive immunization: a performed antiviral product, such as antibody, is administered
    • Active immunization: antigen is administered & causes the onset of the immune response
  11. What are some methods to measure virulence?
    • LD50= how much virus is required to kill 50% of a subject population
    • ID50= how much virus is required to infect 50% of a subject population
    • PD50= how much virus is required to paralyze 50% of a subject population
  12. Cytopathic viruses
    produce virions and kill host cells rapidly (cytopathology)
  13. Non-cytopathic viruses
    produce virions but do not cause cytopathology
  14. Viral dissemination
    Spread of viruses in an infected body
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chapter 13
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chapter 13
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