1. Mechanisms in virus latency

2.  THIS WILL NOT BE ON THE FINAL EXAM!

3. 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.  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.

4. 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.  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.

5. 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).  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).

6. What animal viruses cause latent infections?  All Herpesvirus infections  HSV I and II  EBV  VZV  CMV  Human herpes viruses 6, 7, and 8  HIV  All Herpesvirus infections  HSV I and II  EBV  VZV  CMV  Human herpes viruses 6, 7, and 8  HIV

8. 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  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

9. HSV-I acute versus latent infection

11. HSV I and II