Viruses

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Viruses
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What are viruses?

• Very small
• Obligatory intracellular parasites
• Difficult to isolate, detect, cultivate
• Somewhat like Rickettsia

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What are viruses?

• Contain genetic material
• DNA or RNA
• Protein coat
• Sometimes encased in lipids, carbs and proteins
• Reproduction inside living cells
• No metabolic enzymes
• Use host enzyme
• Problem for drug creators!

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What is a host range?

• Host cells a virus can infect
• Very narrow
• Useful for treating diseases?
• Viral therapy
• Oncolytic viruses
• Range determined by cell receptor sites

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What is a virion?

• One, complete, infectious viral particle
• Contains
• Nucleic acid
• DNA or RNA
• Both can be double- or single-stranded
• Protein coat (capsid)
• Classification based on type of capsid
• Capsomeres protein subunits

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What is a virion?

• Contains envelope (not all)
• Covers capsid
• Lipids, carbs, proteins
• Used to fuse with host PM
• May have spikes

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What types of viruses are there?

• Helical
• Rabies, ebola

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What types of viruses are there?

• Polyhedral
• Animal, plant, phages

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What types of viruses are there?

• Enveloped
• Influenzavirus

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What types of viruses are there?

• Complex
• Many phages
• Additional structures

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What are some viruses I should know?

• No specific epithet
• DNA viruses
• Adenoviridae
• Poxviridae
• Herpesviridae
• Human herpes virus 1, HHV 2, HHV 3
• Papovaviridae
• Hepadnaviridae

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What are some viruses I should know?

• RNA viruses
• Picornaviridae
• Retroviridae
• Lentivirus
• Human Immunodeficiency Virus 1, HIV 2

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Viral Replication
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How do viruses multiply?

• Virus only has a few genes and proteins
• All other proteins come from host cell
• E.g. ribosomes, tRNA, etc.
• Must take over host metabolism

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How do phages multiply?

• Two possibilities
• Lytic cycle
• Lysogenic cycle
• T-4
• About 100 genes
• Multiplication in 5 stages
• Attachment
• Penetration
• Biosynthesis
• Maturation
• Release
• animation

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Whats the difference between lytic and lysogenic
cycles?
Animation
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What else should I know about the lysogenic phase?

• When latent (temperate phase)
• Cant be infected with the same virus again
• Phage conversion can happen
• C. diptheriae produces toxin only in latent
  phase
• C. botulinum, C. cholerae and some streptococci
  also
• Specialized transduction is possible

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How do viruses multiply in animals like us?

• Different mechanism of entry
• Assembly of parts and synthesis also differs
• Different maturation and release

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Whats different about entry?

• Attachment first
• Sites vary from person to person
• Penetration
• Q how does it happen in phages?
• Endocytosis OR
• Fusion (animation)
• HIV

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What happens next?

• Uncoating
• by viral or host enzymes
• Biosynthesis
• nucleic acids
• DNA
• RNA
• proteins

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Is RNA biosynthesis the same?

• Mostly
• Animation
• HIVretrovirus
• animation

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What are the final stages for multiplication in
animal viruses?

• Maturation
• Nucleic acid
• Capsid proteins
• Release
• budding (enveloped viruses) or
• animation
• Rupture

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Viruses and disease
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Is there a connection between viruses and cancer?

• Yes!
• Oncogenic viruses
• 10 of all cancers
• DNA integrates into host cell
• Tumor-specific transplantation antigen (TSTA)
• Cytopathic changes

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Can you give me some examples?

• HPVcervical cancer
• Adenoviridaeadenocarcinoma
• Herpesviridae
• Epstein-Barr (EB) virusBurkitts lymphoma
• HHV-8Kaposis sarcoma
• Hep-Bliver cancer

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Do all viral infections causes symptoms
immediately?

• No
• Latent period for many
• EB may be latently carried in 9 out 10 people
• Herpesviruses can stay for lifetime
• Cold sores
• Chickenpoxshingles (zoster)
• Persistent infections for some
• Usually fatal
• Gradual appearance and worsening of symptoms
• Subacute sclerosing panecephalitis (from measles)

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What are prions?

• Not viruses
• Infectious proteins
• Inherited and transmissible by
• Ingestion
• Transplant
• surgical instruments
• Mad Cow Disease
• Creutzfeldt-Jacob disease