1. Virology

2. Basics of Virology How are viruses transmitted from host to host?
How does a virus
Enter the body?
Enter a host cell?
Replicate?
Exit the cell?
How does the immune system work against a viral infection?

3. Viral entry

4. Viruses are very specific
Species – few related organisms
Rabies – only affects mammals
Polio – primates
Tissue
Flu – lining of respiratory tract
HIV – T-cells

5. What determines the host range?
Entry
Replication
Exit

6. How are viruses transmitted from host to host?
Direct contact
Indirect contact
Air-born – droplets
Food-born
Water-born
Fecal-oral
Vector

7. Reservoirs Organisms where virus is abundant
Probably don’t get sick from the virus
Ex. Wild birds

8. Viral life cycle is important to understand
Virologists study:
Mode of entry
Integration, replication & synthesis
Method of exit
Why??
Interrupt one of these steps
Prevention
Treatment

9. How does a virus enter the body?
Respiratory tract
Flu
Rhinovirus
Hantavirus
GI Tract
Polio
Rotavirus
Skin
Rabies
papillomavirus
Genitals
Papillomavirus
HIV
Herpes
Blood
Hepatitis

10. Many animal viruses are enveloped

11. How can the virus enter the cell?
Injection
Endocytosis
Fuse with membrane
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Low pH dissolves envelope
Uncoat genome
RNA/DNA released

12. How do viruses replicate?
Genome copies
Method varies depending on type of viruses
Translation makes viral proteins
Produce new capsids
Self-assembly

13. Retroviruses Single-stranded RNA viruses Contain reverse transcriptase
Enzyme that synthesizes DNA from RNA
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Ex. HIV

15. Viruses Exit Cell
Budding
Doesn’t kill host cell
Bursting
Kills cell

16. Stability of Viruses

17. Which types of viruses are most stable?
DNA  DNA
Proofreading mechanisms
Few errors
1/1 billion bp
DNA  RNA
Errors 1 million x greater
RNA  DNA
Errors

18. Influenza A Has 8 segments of RNA Changes frequently
New version of flu vaccine
made yearly

19. Why does Influenza A change frequently?
Antigenic drift
Gradual change
RNA has high mutation rate
Minor changes in RNA = minor changes in surface protein
Antigenic Shift
Major changes based on reassortment of RNA segments

20. Reassortment Pigs may serve as a mixing vessel
Co-infection of host by 2 viruses
May mix some human segments & some bird segments
Ex Flu had 3 avian segments, 5 human segments

21. Since mid-1700s, major shifts in Influenza A have occurred about every 30 years
Spanish Flu