6.8 Medical Virology Flashcards
What is the minimal requirements for a virus?
Minimally a virus has DNA or RNA plus a protein shell called a capsid.
What are the functions of the capsid or envelope?
1) Protect nucleic acid when extracellular
2) assist in the entry into a new host cell
3) Help package any essential enzymes.
What is the most common STD?
HPV
What are important viruses in the US?
- HPV
- Influenza
Describe naked viruses
- Are generally hardy in the environment, can survive well outside host and transmit easily via fecal oral route
- Examples: Adenovirus, polyomavirusm and calicivirus
Describe enveloped viruses
- Normally take membranes from infected cells to make envelope
- Are generally sensitive to their environment, easily inactivated by detergents, heat, solvents, and alcohol. Prefer transmission by direct contact or blood
- Examples: Coronavirus, arenavirus, and orthomyxovirus
Describe the Capsid
- Helical or Icosahedral symmetry
- Viral genomes need to be condensed into the capsid or nucleocapsid
- Made of many copies of viral proteins
- Protects the genome and confers shape
- May interact with cells or immune system
Describe viral surface structures
Used for attachment and penetration, may also be involved in release, maturation, or immunity.
Describe Viral Genome
- May be DNA or RNA only
- Can be single or double stranded
- May be segmented but normally linear.
What are the three types of RNA genomes?
1) Positive sense-Translate straight to mRNA
2) Negative sense- Make positive strand, then make mRNA, must bring own RNA dependent polymerase.
3) Ambisense
What must Negitive sense RNA bring in the capsid to infect a cell?
RNA dependent polymerase
Are viruses normally diploid or haploid?
Mostly haploid, with exceptions such as HIV which is Diploid.
What are the 9 steps of viral replication?
1) Recognition
2) Attachment
3) Penetration or fuse
4) Uncoating
5) mRNA synthesis
6) Protein synthesis
7) Genome replication
8) Viral processing and building
9) Cell Exit via Lysis or budding
Describe viral attachment
Randome collision, interaction with host cell receptors, multiple interaction, and fluid nature of plasma membrane
Describe Entry of virus via Fusion
By fusion of viral envelope with plasma membrane leaves viral spike proteins on the surface for possible cell to cell fusion. Only enveloped viruses.
What is viropexis?
Viral entry by receptor mediated endocytosis. Naked viruses enter this way
What is macropinocytosis?
Is a mode of endocytosis in which larger particles are brought into the cell forming an invagination, and then are suspended in small vesicles. These are then fused with lysosomes that help to break down capsid and release viral genome.
Describe bacteriophage entry
Adsorption, intimate contact, and penetration/uncoating
Where do most DNA viruses target?
- The nucleus
- This is so the virus can use the host machinery to make mRNA and then viral proteins.
What can double stranded DNA viruses use to yield viral mRNA’s
RNA polymerase II
What does Hepatitis B virus bring with it when infecting a cell?
It is a partially double stranded DNA virus that brings along reverse transcriptase.
How do most DNA viruses generate mRNA?
Through splicing.
Where do most RNA virus stay?
In the cytosol
What must Retroviruses bring along?
Reverse transcriptase.
What are examples of virus that have segments that code for one protein?
- Orthomyxovirus (influenza)
- Reoviruses (rotaviruses)
What codon initiates mRNA production?
AUG
What is an example of a latent virus?
HPV and Chicken Pox
What is an example of a chronic virus?
Any of the Hepatitis
What causes antigenic drift?
- Mutations in the genome
- RNA likes to mutate, due to little/no proofreading
- Host cells can damage genome via oxidation or deamination thus leading to mutation
Define Attenuated
The disease causing properties are modified to not cause the disease
Define Cold-Adapted
The virus strains replicate efficiently in cooler areas of the nasopharynx at 25 degrees Celsius, to initiate an immune response in the nose
Define Temperature sensitive
The virus strains do not replicate in the lungs where infections occurs.
What does it mean for a cell to be permissive?
The cell must be able to go through replication.
Example:
-Non-permissive CD4 T cells, which make of 95%, infected by HIV are killed before replication can occur.
-Permissive CD4 T cells undergo the full replication cycle of HIV
How can defective particles create a functional virus?
Defective particles may be complemented with a helper virus. Thus A and B by themselves can not make a functional virus, but if they are together they can.
Example: Delta virus needs HBV to make outer proteins
Define Defective interfering (DI) particles
May block a productive infection of normal virus by outcompeting for resources in the infected cell.
Describe Phenotypic mixing
1) Viral genetic diversity via recombination
2) Recombination and template switching
3) Viral genetic diversity via reassortment
What are positive effects of recombination?
- Creation of advantageous genotypes
- Removal of deleterious mutations
- Repair of defective genomes
Describe Antigenic Shift
- Potential for pandemic
- Is the process by which two or more different strains of a virus, or stains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original stains.
Describe Antigenic Drift
- Random Mutations
- Is a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites
What are specimens used for viral diagnosis?
Swabs, fluids, scrapings, biopsy, stool.
What are indications of viral growth in cell culture?
- Growth of cells in a favorable artificial environment
- Plaque assay to titer (quantify virus)
- Virus induced cytopathic effects
- Visualize cytopathic effect (CPE)
What are microscopic methods of identification in the specimen?
- Light microscopy for CPE using biopsied tissues or scrapings
- Fluorescent antibodies
- Direct fluorescent antibody test.
- Electron microscopy: Viruses may be characterized based on morphology and size.
What is direct fluorescent antibody test?
Virus replicating in tissues/cells is detected using a fluorescently labeled antibody
What are serologic procedures to detect a rise in antibody titer or the presence of IgM antibody?
- Enzyme-linked Immunosorbent Assay (ELISA)
- Complement fixation
How do you detect viral antigens in blood or body fluids?
- Radioimmunoassy: Sensitive method for detecting antigens, but exposes lab personnel to radioactivity.
- ELISA “Sandwich: to detect antigens
- Competitive ELISA for antigens
What is Hemagglutinin?
- A viral protein found in the envelope of some viruses that is involved in attachment to respiratory cells; also agglutinates red blood cells of specific animal species in vitro.
- Species with hemagglutinin: Paramyxoviruses and orthomyxoviruses
What is Hemadsorption?
-A method for detecting hemagglutinating viruses that is based on adherence of erythrocytes to infected cells.
What is a Hemagglutination assay?
Hemagglutinin in the viral envelope is detectable by its binding of erythrocytes
What is a Hemagglutination inhibition assay?
Virus specific antibodies interfere with the interaction between hemagglutinin on the virus and the erythrocyte.
What are some methods of detecting viral nucleic acids in blood or in the patients cells?
- DNA probes
- PCR: Polymerase chan reaction: Exponential amplification of a segment of DNA
- Reverse transcription- PCR: for RNA templets
- Real time PCR for qualification (qPCR): uses an internal probe to detect the amplification of the target sequence.
