Viruses Flashcards
What is unique about viral replication compared to other pathogens?
- Obligate Parasites: cannot replicate on their own, lack the machinery to repliate genome
- Must infecy host to replicate
What are the key structural components of the viruses?
- proteins
- envelope
- nucleic acids
Describe the types and characteristics of viral proteins.
- Found in all viruses
- Capsids
- structural proteins
- Icosahedra, Helical
- Enzymes
- M proteins
Describe the components of the enveloped vs. non-enveloped viruses.
- enveloped
- found only in some viruses
- composed of lipids
- makes virus susceptible to detergents
- non-enveloped
- glycoprotein layer
- very hearty, resistant
What are the classifications of DNA viruses?
- Enveloped
- dsDNA (linear)
- dsDNA (circular)
- Non-enveloped
- dsDNA (circular)
- ssDNA (linear)
- dsDNA (linear)
What are the classifications of RNA viruses?
- Enveloped
- retrovirus (+ssRNA —> DNA intermediate)
- -ssRNA
- +ssRNA
- Non-enveloped
- +ssRNA
- dsRNA
What are the 7 virus types according to Baltimore Classification?
- Group I: dsDNA
- Group II: +ssDNA
- Group III: dsRNA
- Group IV: +ssRNA
- Group V: -ssRNA
- Group VI: +ssRNA (reverse transcription)
- Group VII: dsRNA (reverse transcription)
What are the goals of viral replication?
- make viral proteins
- duplicate viral genome
Where do RNA viruses generally replicate? Where do DNA viruses generally replicate?
RNA: cytoplasm
DNA: nucleus
Describe the major viral replication enzymes, their roles, and their sources.
-
RNA-dependent RNA polymerase
- replicates RNA from RNA template
- source: all RNA virses
-
RNA-dependent DNA polymerase
- reverse transcriptase, reverse transcribes RNA to DNA
- source: virus
-
DNA-dependent RNA polymerase
- transcribes RNA from DNA template
- source: host
-
DNA polymerase
- replicates DNA from DNA
- source: host/virus
What are the steps in the viral replication cycle?
- attachment & entry into host cell
- viron uncoating
- transcription of viral mRNA
- translation of viral mRNA (viral protein production)
- replication of viral genome
- assembly of virons (viral proteins encapsulate viral genes)
- virons released from host cell via budding or lysis
What do all viruses transcribe before protein translation?
mRNA (+ssRNA)
What is the general process of viral protein synthesis?
**General Process: **Viral DNA/RNA –> mRNA –> proteins
Exception: Viral RNA retrovirus –> DNA –> mRNA –> proteins
+ssRNA replication
-ssRNA replication
dsRNA replication
RNA retrovirus replication
dsDNA retrovirus replication
ssDNA replication
dsDNA replication
What is cytopathic effect (CPE)?
morphological changes that occur in cells during many viral infection: ballooning, rounding, lysis, giant cell (syncitium), or inclusion body formation
What is Viral Latency?
- virus becomes dormant and ceases production of new virus to hide from immune system
- virus can reactivate at any time, life-long persistence
- ex. herpes simplex virus
What is viral tropism?
specificity of a virus for a specific host tissue; determined by interaction between host cell receptors and viral glycoproteins
How does viral genome size determine pathogenesis?
- size of genome determines how many proteins it can make to take over the host cell
- small viral genome: less flexible in cell targeting; may not have division machinery, must rely on host cell’s machinery
- parovirus B19
- large viral genome: more flexible in cell targeting, carry genes for replication machinery
Cytopathic Effects: enveloped vs. naked
- non-enveloped naked: more virulent, cause cell lysis and killilng
- eveloped: less virulent, can bud off of cell
- synctia formation
- hemogglutination
Define Syncytia formation.
- viral protein spikes get expressed on host cell membrane when enveloped virus buds of; causes host cells to fuse with each other & create a giant cell
- occurs when viruses enter via pH-independent membrane fusion
Define hemagglutination formation.
- viral docking proteins get expressed on surface of host RBC; multiple RBCs cannot fuse like syncytia but then can cross-link and stay aggregated
- occurs when viruses enter via pH-dependent membrane fusion
What is antigenic shift?
- form of viral diversity
- occurs as a result of segmented and rearrangeable genome which means the docking proteins it uses can change quite rapidly
- ex. influenza- can infect multiple organisms, changes frequently
What is antigenic drift?
- form of viral diversity
- occurs as a result of mutations introduced by RNA-dependent RNA polymerase during replication (lacks proofreading mechanism, introduces errors)
Why must -ssRNA use their own RNA-dependent RNA Polymerase to synthesize its +ssRNA for use in translation?
**host doesn’t make RNA-dependent RNA Polymerase
What are the 3 different routes of viral infection/dissemination?
- accute infection
- chronic infection
- latent infection
What occurs in an acute viral infection (use example)?
- EXAMPLE: Poliovirus (enterovirus)
- virus enters the cell
- travels and replicates at primary sites (LNs)
- dimmeniates causing viremia
- infects at secondary replication sites (nervous system)
- spreads to other hosts (i.e. fecal-oral)
What occurs in an chronic viral infection (use example)?
- EXAMPLE: HIV
- acute infection
- chronic lymphadenopathy
- sub-clinical immune dysfunction
- skin, mucous membrane immune defects
- CD4 T cell decline
- systemic innume deficiency
- Anti-HIV antibodies decrease, viral load increases
What occurs in a latent viral infection (use example)?
- EXAMPLE: HSV
- viruses can remain dormant and undetected in cell as episome or provirus
- episome: circular DNA containing viral genome
- provirus: viral genome integrates into host chromosome
- herpes: latent form resides in neurons as episome; reactivated by stress
How are viral PAMPs recognized by host immune system?
- PRRs on host cells detect PAMPs
- ex. dsRNA detected by TLR3, TLR 7/8, RIG-I
How does innate immune system respond to viruses?
- infected cells release IFN that activate macs and NKs
How does adaptive immune system respond to viruses?
- CTLs target cells w/ MHC-I + virgal antigen
What are the host immunopathologies associated with viral infection? Examples?
- IFN: fever, muscle ache, flu symptoms (i.e. influenza)
- CTL: can destroy normal tissue (i.e. liver in HPV)
- CD4+: delayed-type hypersensitivity can cause rashes (i.e. measles & mumps)
- Abs: immune complex hypersensitivity, complement activation, tissue damage (i.e. HBV)
- Chronic inflammation: if viral infection cannot be contained
