Review Flashcards
What is a virus?
- A virus is a small, infectious, obligate, intracellular parasite
-
What are the steps of virus lifecycle?
- Attachment
- Penetration
- Uncoating
- Replication
- Assembly
- Maturation/processing
- Release
What are the methods of viral entry into a host cell?
direct fusion
- virion and envelope fuse to host cell
- nucleocapsid is released into host cell
endocytosis
- virion enters host cell and forms vessicle
- acidification and release of nucleocapsid
Where does viral replication occur?
Most RNA viruses replicate in cytoplasm
- except retroviruses and orthomyxoviruses (flu)
Most DNA viruses replicate in nucleus
- except poxviruses
What must viruses do to make proteins?
All viruses must express their genes as functional mRNAs early in infection in order to direct the cell’s translational machinery to make viral proteins
How do the different types of DNA viruses make their proteins?
dsDNA
- Cellular RNA polymerase => mRNA
ssDNA
- Cellular DNA polymerase => dsDNA => Cellular RNA polymerase => mRNA
How do the different types of RNA viruses make their proteins?
(+) ssRNA
- viral genome acts as mRNA
dsRNA
- viral RDRP
(-) ssRNA
- virion RDRP
Retroviruses
- Reverse Transcriptase
What are the two classification systems used for viruses?
Classical System
- genome type: DNA or RNA
- Capsid type
- Naked or enveloped
Baltimore Classification System
- DNA or RNA
- 7 replication schemes (don’t need to know all 7) just know replication strategy determines classification
What are cytopathic effects?
visible signs of infected cells can be observed with inverted light microscopes
- rounding, shrinkage, lysis
What quantitative assays can be conducted for viruses?
plaque assay
- take sample and sequentially dilute to determine how many plaques form per volume of sample
hemagglutination assay
What are the Three General Approaches for Laboratory Diagnosis of Viral Infections?
Direct detection of viral antigen
- rabies - bullet shaped
- smallpox - dumbbell shaped
Virus isolation
- PCR
Serology
What is viral pathogenesis?
The mechanism by which a virus causes disease in the host
What are the Six steps that viruses employ to propagate and survive?
Enter the cell and translocate the genome to the site of replication
Replicate its genome and produce mRNA
Generate viral proteins
Assemble progeny viruses and then emerge from the cell
Evade host defenses
Disperse and persist in the environment
What are the preferred methods for viruses to gain entry into the host and then target specific cell types?
Respiratory tract (rhinoviruses, influenza) Gastrointestinal tract Genital tract Conjunctiva (eyes) Skin
What are the general patterns of infection for viruses?
Acute Infection
- Quick viral replication and clearance
Persistent Infection
- Prolonged viral load
Latent Infection
- Viral reactivation
Slow virus infection
- HIV
What is the triad model of disease?
host
environment
viral pathogen
What are the types of immune responses?
Nonspecific, innate immunity plays a role shortly after infection and is directed against any virus
Specific immunity requires days to weeks before they are induced or effective in clearing specific viruses
What are some requirements of an effective vaccine?
Safe
Cost Effective
Provides immunity
What stages in the virus lifecycle do antiviral drugs act?
Fusion Inhibitors
- Attachment and entry
- Enfuviritide
Ion Channel Blockers
- Uncoating
- Amantadine and Rimantidine
Polymerase Inhibitors
- Replication
- Acyclovir
Protease inhibitors
- Assembly
- Saquinavir
Neuraminidase inhibitors
- Release
- Zanamivir
What is epidemiology?
The study of the cause, distribution, control, and prevention of disease in a population
What is prevalence vs incidence?
Prevalence
- proportion of cases in a population
Incidence
- proportion of new cases
What is Endemic, Epidemic, Pandemic?
Endemic - localized
Epidemic - nationwide
Pandemic - worldwide
What is gene therapy?
The introduction of genes into a person’s cells to replace or compensate for defective (mutant) genes that are responsible for a specific disease or medical problem.
The therapeutic (good) genes can be delivered by a customized vector such as a virus.
Using genetically engineered viruses to selectively kill cancer cells
What are the applications of gene therapy?
- Gene replacement/augmentation
- Oncolytic virotherapy
- Cell marking/re-population of cells
What is Gene replacement/augmentation?
Especially suited to single gene defects and discrete populations of target cells
e.g., ADA deficiency, cystic fibrosis.
What is Oncolytic virotherapy?
Direct oncolysis
- efficient virus replication and lysis of tumor cells
- ONYX-15 specific lysis of p53-/- cells
Indirect oncolysis (Suicide/toxic genes) - example TK-ACV suicide therapy of tumor cells
Virotherapy + Immune stimulation
- To stimulate the host’s immune system, in particular to cancer cells e.g., HLA genes, immune stimulatory cytokines.
What is Cell marking/re-population of cells?
For autologous bone marrow transplantation in cancer therapy, X-linked SCID
What are the two main ways that viruses transform cells (1st step in cancer development)?
- By activation of cellular signal transduction cascades
- Cell cycle overstimulated = “stepping on the gas” - Interference with the cell cycle controls
- Cell cycle not inhibited = “can’t put on brakes”
- cell that normally would not be replicating undergoes replication
How can we tell that a cancer cell is transformed?
Immortal, high saturation density, no need for GF
Go over the classification of influenzavirus.
Orthomyxoviridae family
3 Types of Influenza: A, B and C
All 3 can infect and cause symptoms in humans, but pandemics caused solely by Type A
What are the functions of influenzavirus proteins?
PB1, PB2, PA
- Code for RNA polymerase
HA, NA
- code for the surface proteins
M2
- M2 ion channel
Go over the influenzavirus lifecycle.
Attachment to sialic acid
Endocytic entry
Uncoating and release of vRNPs into cytoplasm
Translocation of vRNPs into nucleus
Generation of mRNA and positive (+) strands and more – strand RNA genomes
Production of viral proteins
Genomes packaged into pre-assembled capsids
Budding and release of progeny virions
