1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal viruses/other infectious agents. Medgar Evers College Prof. Santos

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal viruses are divided into a number of families, whose name end in –viridae. Examples of RNA and DNA animal viruses that infect vertebrates are

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings RNA viruses 1- picornaviradae 8- paramyxoviridae 2-caliciviridae 9-orthomyxoviridae 3-togaviridae 10-bunyaviridae 4- flaviviridae 11-arenaviridae 5-coronaviridae 12-reoviridae 6-rhabdoviridae 13-birnaviridae 7- filoviridae 14-retroviridae

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA viruses 1- hepadnaviridae 2- parvoviridae 3-papillomaviridae 4-polyomaviridae 5- adenoviridae 6- herpesviridae 7- poxviridae

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive cycle of animal viruses involved in infections Steps are 1- attachment 2- penetration and uncoating 3- synthesis of protein and replication of nucleic acid 4- assembly 5- release

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

7. Attachment Many glycoprotein receptors are on the surface of the cell membrane to which the viral attachment proteins will bind to. Example. HIV must bind to 2 key molecules on the cell surface before it can enter the cell. These are CCR5 and CD4 receptors.

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Penetration and uncoating Naked viruses the virus enters by the process of endocytosis in which the cell membrane surrounds the viral particle and forms a vesicle. After being engulfed, the virus dissolves the vesicle and its released into the cytoplasm.

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enveloped viruses can enter the host by one of two mechanisms; 1-Fusion with the host membrane 2- Endocytosis

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Entry following membrane fusion The envelope of the virus fuses with the cell membrane after attachment to a host cell receptor. This is enhanced by fusion proteins on the surface of the virus. Following fusion, the nucleocapsid is released directly into the cytoplasm. The nucleic acid separates from the protein coat.

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Entry by endocytosis The host plasma membrane surrounds the whole virion and forms a vesicle. The envelope of the virion then fuses with the plasma membrane of vesicle. Nucleocapsid is released. Separation of nucleic acid from the capsid.

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nucleic acid replication/protein synthesis Involves transcription or the production of messenger RNA from either DNA or RNA.

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Assembly The capsids and genome are assembled together. Most RNA viruses are assembled in the cytoplasm while most DNA viruses are put together in the nucleus.

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Release Enveloped viruses- budding Naked virus- are released when cell dies due to the virus triggering apoptosis

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 main categories of relationships between virus and host 1- Acute 2- Persistent

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acute Short lasting The Immune system eventually clears the virus from the body Unlike a phage infecting a bacteria during a lytic infection, the host can survive.

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Persistent infection. 2 types 1.Latent infection in which a symptomless period is followed by reactivation of the virus. The agent can’t be detected until the disease is activated. Examples are Herpes simplex 1, Herpes simplex 2, and Chickenpox (varicella).

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. Chronic infection- an infection that can be demonstrated at all times. Disease symptoms may be present or absent during an extended period of time or may develop late. In the carrier state the infectious agent is constantly produced and can be detected in the bloodstream. Examples are Hepatitis B, Hepatitis C, and Congenital Rubella.

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Viroids and Prions: The Simplest Infectious Agents Viroids – Are circular RNA molecules that infect plants and disrupt their growth. – Consists of a single strand of RNA – The viroid RNA is circular and resistant to nucleases.

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prions – Are slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals. – Propagate by converting normal proteins into the prion version. Figure 18.13 Prion Normal protein Original prion New prion Many prions

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prions can cause infections in sheep, humans, cows, deer, elk, and the mink. Most agents affect the central nervous system.