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Mechanisms in virus latency. THIS WILL NOT BE ON THE FINAL EXAM!. Why is every viral infection not productive?. Bacteriophages -  - When  infects a bacterial cell, there are two possible outcomes a lytic infection in which new viruses are made, or

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why is every viral infection not productive
Why is every viral infection not productive?
  • Bacteriophages -  - When  infects a bacterial cell, there are two possible outcomes
    • a lytic infection in which new viruses are made, or
    • lysogeny in which the bacteriophage integrates its DNA genome into the host cell DNA and new viruses are not made.
  • What benefit does lysogeny provide for the virus?
    • To exchange a chancy existence for one in which reproduction of progeny is assured.
    • As long as the bacteria keep reproducing, the virus, in the form of the viral genome, will also be reproduced.
  • Does lysogeny provide any benefit to the host?
    • It may carry a selective value for the host and confer new characteristics to the host.
do animal viruses undergo lysogeny
Do animal viruses undergo lysogeny?
  • Animal viruses
    • Animal viruses don’t undergo “lysogeny”, but some do cause latent infections.
    • Latent infections in animal viruses are similar to lysogeny in bacteriophages in that:
      • During a latent infection, the virus is quiescent with no progeny being produced.
      • The virus co-exists with the host and survives as long as the host survives
    • Latent infections in animal viruses differ from lysogeny in bacteriophages in several ways:
      • With the exception of HIV, which is a retrovirus, the virus does not integrate its DNA, into the host cell DNA, but remains as a episome.
latent infections
Latent infections
    • The latent infection begins with a productive infection and then the virus becomes latent.
    • The productive infection may occur in one cell type while the latent infection is found in a different cell type.
  • Latent infections can reactivate to cause a productive infection, and the new virus particles can infect a new susceptible host. The original host still retains a latent infection.
    • Reactivation may be due to a breakdown of the immune system or the patient may be experiencing some sort of stress.
  • The reactivation disease may be different from the original productive infection (chicken pox versus shingles in varicella-zoster infections).
what animal viruses cause latent infections
What animal viruses cause latent infections?
  • All Herpesvirus infections
    • HSV I and II
    • EBV
    • VZV
    • CMV
    • Human herpes viruses 6, 7, and 8
  • HIV
hsv i
HSV-I
  • The initial productive infection takes place in epithelial cells of the oral cavity.
  • HSV is neurotropic and it establishes a latent infection by entering a sensoty nerveaxon ner the infection site.
  • The virus then moves to the neuron’s nucleus in the trigeminal nerve ganglion