Mechanisms in virus latency

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.

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.

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).

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

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

9. HSV-I acute versus latent infection

11. HSV I and II