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88 Cards in this Set
- Front
- Back
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What is a virus?
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A self-repllicating nucleoprotein with a single type of nucleic acid without a source of energy. An obligate molecular parasite
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How big are viruses?
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20-350 nm
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What is the viral encoded protein coat called?
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Capsid
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What are the structural units of the capsid?
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Capsomers
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What are 5 capsomers called?
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Pentamer
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What are 6 capsomers called?
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hexamer
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Where are hexamers?
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At the face and edges of the capsid
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Where are pentamers?
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at the vertices of the capsid
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What is the viral envelope made of?
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lipoprotein
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What are teh things that project from the surface of the virus envelope?
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Peplomers
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What allows recognition of cellular receptors?
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Viral attachment proteins
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What bridges between the nucleocapsid and the internal membrane of the envelope?
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Matrix proteins
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What viral form has 12 vertices and 20 equilateral triangular faces?
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Icosahedral
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What are the three forms of icosahedral symmetry?
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All pentamers with trimer capsomers. Simple pentamers at the 12 vertices and hexamers on the 20 faces. Or all hexamers with dimer capsomers.
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How are viruses classified?
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By host, by mode of transmission, by organ specificity, by morphology.
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What is syncytia?
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A cytopathic effect. Viral proteins are inserted into the membrane which causes the cells to bunch together.
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What are inclusion bodies?
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An aggregation of viral structural proteins
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What is transformation?
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When cells are close together and the pile up. Also called microtumor.
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How do you find the titer of a qualitative titration?
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It is the reciprocal of the last dilution of the sample at which the reaction was detectable.
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How do you find the titer of a quantitative titration?
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It is the reciprocal of the last dilution of the sample at which the sample was detectable multiplied by the quantity of the reaction.
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What is the eclipse period?
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The interval between viral penetration and production of first progeny.
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What is the maturation period?
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The interval between when the first progeny particles become detectable inside the cell and when progeny are released.
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What are the stages of viral replication?
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Adsorption, penetration, maturation, release
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Does adsorption require energy?
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No, so it is independent of temperature
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Is penetration temperature dependent?
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Yes.
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What are the two mechanisms of penetration?
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Fusion or endocytosis
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What is the significance of the eclipse period?
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THE VIRUS CAN'T BE DETECTED.
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Where are RNA viruses replicated?
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In the cytoplasm
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Where are DNA viruses replicated?
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In the nucleus
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What are the three forms of release?
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Cytolysis, budding, exocytosis
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How does exocytosis work?
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Viruses get their envelopes from internal cellular membranes and form cytoplasmic vesicles. The vesicle membrane fuses with the plasma membrane.
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What is positive ssRNA?
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The viral single stranded RNA can act as mRNA so can act immediately.
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What is negative ssRNA?
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The viral single stranded RNA is complementary to mRNA. So makes cRNA for message.
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How do retroviruses replicate?
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They use a virally encoded core protein (reverse transcriptase) to make DNA. (RNA dependent DNA polymerase) Viral DNA then integrates into the cellular DNA.
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What is polycistronic mRNA?
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The mRNA can be spliced after it is transripted. Or the polyprotein can be spliced after it is translated.
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What is steady state?
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Cell survives. Cell may or may not release progeny.
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What is latency?
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The viral genome remains in the cell but there are no viral progeny. Viral genome persists as a provirus or an episome.
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What is transformation?
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The virus alters the cellular phenotype and function.
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What is a provirus?
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The viral genome is integrated in cellular DNA.
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What is transduction?
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Retroviruses use reverse transcriptase to accidentally copy cellular mRNA, and the viruses get cellular information. Can pick up proto-oncogenes
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How doe viruses mutate?
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2 viruses can be infecting the cell at once, there is intramolecular recombination and they switch strands of DNA/RNA. Retrovirusescan copy cellular mRNA by mistake and get cellular information,
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What is the incubation period?
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The interval between infection and the onset of clinical signs
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What happens when macrophages encounter viral antigen?
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The antigen binds to MHC II on the macrophage surface and the macrophase releases IL-12.
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What does IL-12 do?
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It activates CD4 cells which condition macrophages. Then the macrophages activate CD 8 cells
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What happens to a CD 8 cell after it is activated by a conditioned macrophage?
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It becomes a cytotoxic T lymphocyte that kills infected cells.
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Macrophages with viral antigen on them produce IL-4. What does IL-4 do?
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It turns CD4 cells into TH2 cells, which then activate B cells to become plasma cells.
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What does the humoral immune system do?
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Decreases infectious dose and reduce severity of the disease.
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What does cell mediated immunity do?
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Limit the spread of the virus and clean up the infection
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What is passive immunity?
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Antibodies come from the mother
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What is active immunity?
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CD4/TH2 cells turn B cells into plasma cells
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What do neutralizing antibodies do?
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They inhibit infection, distort the virus capsid, prevent attachment of virus to cells
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What do non-neutralizing antibodies do?
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They opsonize and induce type 3 hypersensitivity
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In steady state infection, where does most of the damage come from?
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Alteration of cell function and MHC class 1 can drive tissue destruction
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How do viruses directly induce immunosuppression?
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By lysing macrophages and lymphocytes, bu causing immune cell disfunction, by decreasing cytokine production.
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How do viruses indirectly induce immunosuppression?
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By blocking production or processing of cytokines, by binding and inactivating cytokines, by altering CD8 T cells, by blocking cell-surface display of MHC class 1
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What is immunological tolerance?
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Viral antigens mimic self and induce auto-immune problems.
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What is the major site of viral persistence?
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Nervous tissue
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What are the stages of pathogenesis?
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Entry, amplification of titer via replication, viral spread to secondary replication sites, replication at site of exit.
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Why does pox virus cause shock?
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Nitric oxide synthetase gene causes hypotension
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What determines virus tropism?
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VAPs- Viral Attachment Proteins
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What is the pathogenic mechanism of pox virus?
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enters skin, multiplies in regional lymph node, enters bloodstream, causes primary viremia, multiplies in spleen and liver, causes secondary viremia, goes back to skin and multiplies in focal areas. The rash can transmit the virus.
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What is the pathogenic mechanism of enterovirus?
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Invades and multiplies in small intestine, multiplies in enteric lymph nodes, causes viremia, invades and multiplies in the central nervous system, spreads intraneurally, antibodies appear in serum, paralysis. Virus is excreted in feces
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What is the pathogenic mechanism of herpes virus?
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Virus invades respiratory system, macrophages are infected, primary viremia, virus rtansforms T cells, lymphoma, virus invades nerves, paralysis results. The virus replicates and is transmitted via feather follicle epithelium
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What are four molecular mechanisma of viral pathogenesis?
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Repression of MHC Class 1 (so cytotoxic t lymphocytes can't recognize infected cells), synthesis of sterois hormones that suppress the immune system, expression of superantigens, inhibits interferon production
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Name some viruses with multiple hosts
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rabies, togaviruses, bunya viruses, orbiviruses, influenza a, pox viruses, henipavirus, sars
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What influences transmission efficiency?
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titer, duration of shedding, stability of virus, infectious dose required to establish an infection, probability of contact with a susceptible host, herd immunity, seasonal factor
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How can you Id viruses?
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PCR, nanoparticles, microfluidics
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What are characteristics of an ideal vaccine?
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Will illicit immune response as good as wild-type infection would, will induce cell mediated immunity, will inducea full complement of antibodies, no adverse reactions, will be stable, easy to administer, if it's modified live: won't revert to virulent, doesn't recombine with wild type, doesn't persist, lacks oncogenic potential
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What are problems with live vaccines?
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Can revert, recombine, cause immunosuppression, have vertical transmission, induce a carrier state
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What are problems with killed vaccines?
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Require boosters, have a restricted immune response, not DIVA compatible.
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What are some improved vaccine delivery methods?
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Aerosol dispersion of biodegradable polymers, transcutaneous, transgenic edible plants
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Where does interferon alpha come from?
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leukocytes.
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Where does interferon beta come from?
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fibroblasts
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Where does interferon gamma come from?
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activated t lymphocytes
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What is different about interferon gamma?
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It is mitogen induced, not viral induced. It islabile, not stable.
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What can induce interferon production?
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Double stranded RNA, lipopolysaccharides
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What are the five kinds of antivirals?
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Fusion inhibitors, ion channel inhibitors, polymerase inhibitors, protease inhibitors, neuraminidase inhibitors
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What do the ion channel inhibitors work?
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(amantadin and ramantadine) interfere with viral protein required for uncoating
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How do the polymerase inhibitors work?
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They are nucleoside analogs.
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How do protease inhibitors work?
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They inhibit post- translational cleavage events
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How do neuraminidase inhibitors work?
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Bind tightly to amino acids in catalytic site of neuraminidase, thereby inhibiting the enzyme
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Which cells are the easiest to transform?
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Non-permissive
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What are epi-genetic changes?
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They result from alterred gene expression patterns
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What are the stages of transformation?
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Mutation, proliferation advantage, natural selection
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What are some tumor suppressor proteins?
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p53, p73, pRB, E2F
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How does transformation occur with DNA viruses?
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Viral oncognenes persist with or without integration or there is a continuos expression of viral oncogenes
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In adenoviruses what does E1A do?
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Master gene-controls replication. It binds pRB and induces s-phase
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In adenoviruses what does E1B do?
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It encodes a protein that facilitates the transport of viral MRNA from the nucleus to the cytoplasm. It binds p53 and blocks apoptosis.
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