Microbiology Virology
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- 3 outcomes of a viral infection?
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1. Abortive/failed
2. Cell death (lytic)
3. Virus production w/o death (nonlytic). These are presistent. - 3 categories of persistent infections.
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1. Chronic.
2. Latent.
3. Transforming. - 5 characteristics of viruses.
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1. Obligate intracellular parasites.
2. Lack ATP synthetic machinery.
3. Lack protein synthetic machinery.
4. Lack complex enzymes for metabolism.
5. Rely on host cells for most of replication. - 6 ways viruses can affect the host cell.
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1. Shut down host cell protein translation, causing cell death.
2. change growth properties of cell.
3. Change stability/regulation of hot proteins.
4. Change host RNA synethesis.
5. Change host DNA replication.
6. Change host anti-viral response. - Describe virus structure.
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Contains:
1. Capsid = protein shell surrounding genome. Either icosahedral or helical.
2. Envelope = makes nonstable b/c requires aqueous environment. - 6 steps in viral life cycle.
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1. Attachment.
2. Entry.
3. Uncoating
4. Replication.
5. Assembly.
6. Release. -
Describe how virus enters the cell:
a. naked
b. enveloped -
a. Naked via receptor-mediated endocytosis;
b. Enveloped by either:
1. Receptor-mediated endocytosis, or
2. Membrane fusion w/cytoplasmic membrane. - What is the eclipse period?
- Time when nucleic acid is inside the cell,but is not infectious.
- How does replication/translation of DNA & RNA viruses differ?
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DNA - use host RNA/DNA polymerase.
RNA - use viral transcriptase. - Where do nonenveloped DNA viruses replicate? nonenveloped RNA viruses?
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DNA in nucleus.
RNA in cytoplasm.
(CHECK ON THIS INFO) - What is a serotype?
- Different antigens on the capsid. Neutralizing Ab differ for each serotype.
- 3 factors that affect the extent of a viral disease.
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1. Host range (what types of cells are injected)
2. dose/pathogenicity
3. State of host. - List 3 small DNA viruses.
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1. Adenovirus
2. Parvovirus
3. Papovavirus - Characteristics of Adenovirus
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Linear, ds DNA.
Nonenveloped c spikes for attachment.
Causes:
1. Respiratory infection.
2. Conjuctivitis.
3. GI tract (u. subclinical)
4. ARD (crowding/stress) - Characteristics of Parvovirus.
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Small, ss DNA.
Non-enveloped.
Two viruses:
1. B19 - infects immature erythroid cells. 5th disease (erythema infectiosum).
Polyarthritis in adults. Can cause severe anemia.
2. AAV - no known diseases. - Characteristics of Papovavirus.
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Circular, ds DNA.
Non-enveloped.
3 viruses to know:
1. Papillomavirus.
2. Polyomaviruses: (both cause mild respiratory but may be carried latently in kidney/tonsil.)
a. BKV- multiples in urinary tract. Kidney tranplant failure.
b. JCV - progressive multifocal leukencephalopathy. - List 2 large DNA viruses.
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1. Herpes.
2. Pox (Variola & Vaccinia).Variola caused smallpox. - Characteristics of Smallpox.
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Large, Very complex ds DNA.
Enveloped, but stable.
Caused by Variola virus of Pox family.
There is no animal reservoir for smallpox. - Describe pathogenesis of small pox.
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Virus in respiratory secretions & skin lesions. Hu-Hu contact leads to RT infection → to regional lymph nodes → 1 viremia → internal organs → 2 viremia → skin eruptions.
Death: organ failure.
2° complications: pneumonia.
Incubation period: 2 weeks. Symptom free but infectious. - Structural characteristics of Herpes Virus.
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ds linear DNA.
Enveloped.
Have glycoprotein spikes used for penetration.
Icosahedral capsid.
*Between nuclear capsid & envelope is e- dense tegument which contains proteins that are ready to be released after fusion. - Name 3 common properties of productive herpes infections.
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1. cytolytic.
2. viral DNA synthesis occurs in nucleus, carried out by virus-encoded enzymes.
3. Nucleocapsids assemble in the nucleus & gain an envelope. - What are the 3 herpes subfamilies?
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1. alpha (1,2,VZV)
2. beta (CMV,6,7)
3. gamma (EBV, 8) - Characteristics of alpha subfamily of herpes.
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Variable host range.
Rapid repro cycle.
Latency established in neurons.
Members: 1,2,VZV. - Characteristics of beta subfamily of herpes.
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Restricted host range.
Slow repro cycle.
Latency established in lymphocytes, monocytes.
Cytomegalic.
Members: CMV, 6,7. - Characteristics of gamma subfamily of herpes.
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Restricted host range.
Latency established in lymphoid cells.
Members: EBV, 8. - 2 requirements for latency to be established:
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1. Supression of cytolytic activities.
2. Avoidance of host antiviral defenses.
It doesn't kill the cell and the cell doesn't kill it. - Characteristics of Herpes Simplex Viruses infections.
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Infection via epithelium of oral/genital/ocular or by break in skin.
HSV1- usually oral/ocular.
HSV2 - usually genital.
Primary oral infection mostly asymptomic & occur b/w 6 mon. & 3 yrs.
Primary genital causes vesicular, ulcerative lesion, fever, malaise, dysuria, localized lymphadenopathy.
Primary oral infection: keraconjuncitivit with vesicles & dendritic corneal ulcerations. - How is latency established by Herpes Simplex virus?
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Neurons of PNS infected with virus released from epithelial cells.
Retrograde spread within axons.
Latency ion cell bodies of DRG.
Note: Latency in non-dividing cells so that they don't need to replicate their genome. - What are HSV Latency-Associated Transcripts (LAT)?
- A transcript spliced to generate a stable intron encoded w/i the HSV genome. LATs appear to maintain HSV in transcriptionally inert, latent stage and prevent apoptosis.
- Describe the neuroinvasiveness of HSV infections.
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Low neuroinvasiveness.
Highly neurovirulent. - What is recurrent herpetic stromal keratitis?
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Autoinflmmatory reaction (T-cell dependent) that is assoc with HSV.
Underlying mechanisms:
1. Molecular mimicry - Ab destroy host.
2. Bystander activation - T cells respond to antigen X and end up responding to antigen Y.
3. Inflammatory cells release cytokines, chemokines & GF that dirupt balance b/w angiogenic and antiangiogenic activity. - Treatment of HSV infections:
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Acyclovir & Ganciclovir
(Guanosine analogues)
Triphosphorlated form is incorporated into growing DNA chain for that DNA replication terminates prematurely.