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Microbiology Virology


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3 outcomes of a viral infection?
1. Abortive/failed
2. Cell death (lytic)
3. Virus production w/o death (nonlytic). These are presistent.
3 categories of persistent infections.
1. Chronic.
2. Latent.
3. Transforming.
5 characteristics of viruses.
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.
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.
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.
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?
DNA - use host RNA/DNA polymerase.
RNA - use viral transcriptase.
Where do nonenveloped DNA viruses replicate? nonenveloped RNA viruses?
DNA in nucleus.
RNA in cytoplasm.
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.
1. Host range (what types of cells are injected)
2. dose/pathogenicity
3. State of host.
List 3 small DNA viruses.
1. Adenovirus
2. Parvovirus
3. Papovavirus
Characteristics of Adenovirus
Linear, ds DNA.
Nonenveloped c spikes for attachment.
1. Respiratory infection.
2. Conjuctivitis.
3. GI tract (u. subclinical)
4. ARD (crowding/stress)
Characteristics of Parvovirus.
Small, ss DNA.
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.
Circular, ds DNA.
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.
1. Herpes.
2. Pox (Variola & Vaccinia).Variola caused smallpox.
Characteristics of Smallpox.
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.
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.
ds linear DNA.
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.
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?
1. alpha (1,2,VZV)
2. beta (CMV,6,7)
3. gamma (EBV, 8)
Characteristics of alpha subfamily of herpes.
Variable host range.
Rapid repro cycle.
Latency established in neurons.
Members: 1,2,VZV.
Characteristics of beta subfamily of herpes.
Restricted host range.
Slow repro cycle.
Latency established in lymphocytes, monocytes.
Members: CMV, 6,7.
Characteristics of gamma subfamily of herpes.
Restricted host range.
Latency established in lymphoid cells.
Members: EBV, 8.
2 requirements for latency to be established:
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.
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?
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.
Low neuroinvasiveness.
Highly neurovirulent.
What is recurrent herpetic stromal keratitis?
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:
Acyclovir & Ganciclovir
(Guanosine analogues)
Triphosphorlated form is incorporated into growing DNA chain for that DNA replication terminates prematurely.

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