1. VIRUSES CHAPTER 10

2. What are Viruses? Obligate intracellular parasites Viral components
Nucleic acids
Capsid
Envelope

3. Viral Shapes and Sizes
Helical
Polyhedral
Spherical (Enveloped)

4. Infectious Properties
Viral Host range
From 1 species (polio virus) to many (Influenza virus)
Viral specificity
From 1 cell type (Hepatitis B virus) to several (CMV in GIT, lungs, spleen)
Viral Origins
? Co-evolution with cells
? Degeneration

5. Virus Classification 108 families so far Classification based upon
Pathogens for all life forms
Classification based upon
Nucleic acid type
Single strand vs. double strand chromosome
+ versus – single strand
Enveloped versus “naked"

6. 11 RNA Virus Families + strand RNA virus Family Picornaviridae
RNA dependent RNA polymerase makes a - strand intermediate template
3 Genera:
Enterovirus
Includes poliovirus,
Hepatovirus
Includes Hepatitis A
Rhinovirus
Attach to molecules of nasal mucous membranes, cause some colds

7. Unique RNA Virus Cycle 2 + strands Retroviridae
Reverse transcriptase unique enzyme
RNA to DNA
Provirus synthesis
Provirus integrates into host DNA
No removal
Activation and transcription later produces more viruses
Includes HIV

8. Antisense Virus Rhabdoviridae
RNA dependent RNA polymerase makes a Sense strand (+) for mRNA
Antisense (-) strand as chromosome
Includes rabies virus

9. ds RNA Chromosome Reoviridae Non-enveloped
Cause respiratory and intestinal infections in adults
Severe diarrhea in infants caused by Rotavirus
Animals may be affected by some members

10. ds DNA Virus Families Adenoviridae Cause many “colds”
Highly stable over pH and temperature changes
10-30% of infant diarrhea
Infection may be associated with a rash

11. ds DNA Viruses (cont.) Herpesviridae > 100 species Latent viruses
Herpes simplex virus
Varicella virus
Epstein Barr virus

12. ds DNA Viruses (cont.) Papovaviridae Cause skin and genital warts
DNA may not be integrated into the host chromosome
13 papilloma viruses are associated with cervical cancer
GardasilTM

13. ss DNA Viruses Parvoviridae ss DNA viruses
Unrelated viruses or host genes needed to allow replication
Human disease known as 5th disease (Erythrovirus)
Canine Parvovirus gastroenteritis
Dependovirus genus must coinfect with Adenovirus or Herpesvirus for replication, no human diseases

14. Emerging Viral Diseases
Considerations:
Reservoirs in animal populations
Vectors
Mutation/Recombination frequencies
Immunity vs. containment (after rapid air travel of incubating patients)

15. Viral Replication General Characteristics of Replication Adsorption
Penetration (virus or chromosome)
Synthesis
Maturation
Release

16. Lytic Bacteriophages
Virulent T-even bacteriophages

17. Bacteriophage growth
Plaque Assay
Virion

18. DNA Animal Viruses Chromosome replication in host cell nucleus
Cytoplasmic ribosomes for viral mRNA translation
Viral capsid proteins must return to nucleus for maturation phase
Envelope proteins to plasma membrane

19. RNA Animal Viruses Use RNA-dependent RNA polymerase
Cytoplasmic chromosomal replication and protein synthesis
+ strands always needed for mRNA
Chromosome may be + strand or – strand, depends on virus family

20. Retrovirus Cycle
Use RNA-dependent DNA polymerase (Reverse transcriptase)
+ strand chromosome acts as template for ds DNA provirus
Later transcription of provirus allows for virus production

21. Early Virus Culture Methods
Live animals
Research
Eggs
Vaccines
Allergies

22. Cell Cultures for Viral Growth
Primary – harvested animals cells
Continuous – cancer or immortalized cells

23. Viral Cytopathic Effects
Cytopathy
Cell shape/size
Cell adhesions (contact inhibition)
Transformation (cells divide forever)
Teratogenic effects
CMV, HSV-1, Rubella
TORCH series (Toxoplasma, Others like Chicken pox and Hepatitis B, Rubella, CMV, HSV

24. Viruses and Cancer
Cancer - Triggering of rapid uncontrolled cell division
Mechanisms of cancer causation
Block of tumor suppression genes
Proto-oncogene activation
Oncogenes (may be carried by DNA cancer viruses)