Virology

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Virology
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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?

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Viral entry
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Viruses are very specific

• Species few related organisms
• Rabies only affects mammals
• Polio primates
• Tissue
• Flu lining of respiratory tract
• HIV T-cells

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What determines the host range?

• Entry
• Replication
• Exit

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How are viruses transmitted from host to host?

• Direct contact
• Indirect contact
• Air-born droplets
• Food-born
• Water-born
• Fecal-oral
• Vector

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Reservoirs

• Organisms where virus is abundant
• Probably dont get sick from the virus
• Ex. Wild birds

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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

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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
• HIV

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Many animal viruses are enveloped
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How can the virus enter the cell?

• Injection
• Endocytosis
• Fuse with membrane
• http//darwin.bio.uci.edu/faculty/wagner/hsvbindi
  ng.html
• Low pH dissolves envelope
• Uncoat genome
• RNA/DNA released

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How do viruses replicate?

• Genome copies
• Method varies depending on type of viruses
• Translation makes viral proteins
• Produce new capsids
• Self-assembly

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Retroviruses

• Single-stranded RNA viruses
• Contain reverse transcriptase
• Enzyme that synthesizes DNA from RNA
• http//www.whfreeman.com/kuby/content/anm/kb03an01
  .htm
• Ex. HIV

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Viruses Exit Cell

• Budding
• Doesnt kill host cell
• Bursting
• Kills cell

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Stability of Viruses
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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

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Influenza A

• Has 8 segments of RNA
• Changes frequently
• New version of flu vaccine
• made yearly

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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

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Reassortment

• Pigs may serve as a mixing vessel
• Co-infection of host by 2 viruses
• May mix some human segments some bird segments
• Ex. 1957 Flu had 3 avian segments, 5 human
  segments

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

• Spanish Flu - 1918

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