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93 Cards in this Set
- Front
- Back
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Localized Infection
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newly released virus infects adjacent cells
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Systematic Infection
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Organs, wide spread
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Neurotropic
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Virus can infect neural cells
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Tropism
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predilection of virus to infect certain tissues and not others.
4 parameters: susceptibility, permissibility, accessibility, local immune responses. |
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Epidemiology
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The study of occurrence of disease in a population.
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Fomite
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object that can transmit infection
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Neutralization tests
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A test to determine the antimicrobial activity of a serum by inoculating a susceptible animal with a mixture of the serum and the virus or other microbe being tested.
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Acute Infection
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rapid production of infectious virus followed by rapid resolution and clearing of infection by the host.
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Chronic Infection
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Persistent infections that are eventually cleared.
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Polarized release
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Directional release of virions from polarized cells
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Hematogenous Spread
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Spread throughout the body via blood. 2 phases of viremia.
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Viremia
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presence of infectious virus particles in blood
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Primary viremia
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virus released into the blood after initial replication at the site of entry. Initial sites of entry: skin, mucous membrane, Resp. T, GI Tract. Move through blood to
Replication sites: muscle, liver, spleen, blood vessels. |
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Secondary viremia
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Secondary viremia delayed appearance of infectious virus in the blood as a consequence of disseminated infections.
Replication sites: skin, mucous membrane, lungs, kidney, GI tract, brain. |
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Neural Spread
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spread of virus through neurons.
Enter the neuron at axon, sensory terminal or cell body. Replication occurs in cell body (transcription and translation). Assemble virus particles egress from neuron in a directional manner. Virus replicates in ganglea. |
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Infection of nervous system
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3 types of infections: neurotropic, neuroinvasive, neurovirulent
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Neurotropic
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Virus can infect neural cells.
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Neuroinvasive
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virus can enter CNS after infection of a peripheral site.
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Neurovirulent
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Virus can cause disease of nervous tissue, manifested by neurological symptoms and often death.
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Virus Shedding and transmission
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Shedding: release of infectious viruses from an infected host.
Respiratory secretions: measles Saliva: rabies, feline leukemia Feces: Polio Blood: Ebola, Marburg Urine: Hanta Semen: HIV, HEP B Skin lesions: Herpes Simplex |
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Virulence (viral)
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capacity of infection to cause disease.
Virulent Avirulent: no disease Atenuated: not that severe |
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Zoonosis
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disease shared by animal and humans
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Vertical transmission
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transfer of viruses between parent and offspring.
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Iatrogenic transmission
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activity of healthcare worker leads to infection.
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Nosocomial transmission
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individual infected in a hospital or medical facility
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Mechanisms of transmission
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Aerosol
Food and water Fomites Body secretions Sexual activity Birth Transfusion or transplant Zoonoses |
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Herd immunity
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failure of disease to progress due to natural immunity of herd or through vaccination of certain members of the herd.
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Controlling spread
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Quarantine
Vector elimination Immunization Antivrals |
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Patterns of infection
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Acute
Inaparent Persistent Latent, reactivating Chronic, Slow Transforming |
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Acute Infection
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Rapid production of infectious virus, followed by rapid resolution and clearing of infection
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Persistent infection
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infected cells or virions are not cleared efficiently by adaptive immune response, and virus particles or viral gene products continue to be produced for long periods.
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Chronic
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persistent infections that are eventually cleared.
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Latent
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persistent infections that last the life of a host.
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Transforming
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special class of persistent infection. Infected cells may exhibit altered growth properties and begin to proliferate faster than uninfected cells.
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Prodromal
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spread before obvious symptoms, but shedding. Period can be extremely infectious.
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What are the most common methods for viral entry into a host?
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Respiratory tract: mechanical barriers (cilium, mucus, protective structure)
Alimentary tract: epithilial cells, villi, microvilli on intestine lining. Urogenital tract Eyes Skin |
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List 4 parameters that determine viral tropism
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Susceptibility: receptor
Permissivity: virus may require particular protein Accessibility: acess to tissue Local immune response: different areas different responses |
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Describe most common mechanisms for shedding a virus
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Respiratory secretions
Saliva Feces Blood Urine, semen, and milk Skin |
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Describe ways that viruses can overcome plant cell walls.
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Viruses can use channels between cells that allow movement.
Proteins also allow virus to move through plasmodesma. |
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What are some of the common signs of virus infection in a plant?
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Local lesions like chlorotic and necrotic spots and ringspots, systemic symptoms like yellowing, dwarfing, mosaics.
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Describe the mechanisms for establishment of a persistent infection
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Ineffective intrinsic or innate immune response.
Perpetuation of persistent infection by modulating the adaptive immune system. Infection of tissues with reduced immune surveillance. Direct infection of the cells of the immune system. |
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Vaccines
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Stimulate immune memory.
Active or passive immunization. |
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Types of Vaccines
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Live attenuated virus
Inactivated or "killed" virus New vaccine technologies Adjuvants and vaccine delivery systems |
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Advantages and disadvantages of Live virus vaccine
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Advantages: generalized immune system activation, polyclonal, immunity is long-lived and cross reactive.
Disadvantages: contaminants, low level virulence, back mutations, interference, secondary spread, unstable. |
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Examples of Live virus vaccines
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adenovirus, measles, mumps, polio (Sabin), rubella, smallpox, varicella, yellow fever.
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Inactivated virus vaccines +, -
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(+)Low risk of contamination, more stable
(-)More doses and boosters, no local immunity, high concentration is needed, potentiation of disease. |
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Examples of Killed virus vaccines
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hep A, polio (Salk), flu, rabies
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New Vaccine Technologies
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subunit vaccines, DNA vaccines, live virus vectors
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Subunit vaccines
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Include only the antigens that best stimulate the immune system, lower risk of adverse reactions
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Examples of subunit vaccines
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HEP B, HPV
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DNA Vaccines
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Use genes that code for antigens, transfection, syringe or gene gun.
No need for developing delivery method. |
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Adjuvants
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Immunostimulatory substances
-Presentation of antigen as particles -Localization of antigen to the site of inoculation -Direct stimulation of the innate immune system |
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Delivery Systems
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Hypodermics, air guns, emulsions, artificial particles, direct injection of fine powders under skin, oral delivery, edible particles
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Vaccines as immunotherapy
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patients already infected with virus.
Can provide patient with cytokines, antibodies, or lymphocytes |
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Recombinant vaccine
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Recombinant vaccines are created by utilizing bacteria or yeast to produce large quantities of a single viral or bacterial protein. This protein is then purified and injected into the patient, and the patient's immune system makes antibodies to the disease agent's protein, protecting the patient from natural disease.
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Targets for antivirals
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Attachment
Penetration and uncoating Synthesis of viral proteins Replication of viral nucleic acids Integration Viral morphogenesis |
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FDA Approval process
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Preclinical: Lab and animal studies
Phase I trial: establishes drug is neither lethal nor toxic Phase II trial: compare to existing treatment or placebo, 200-300 patients. Phase III trial: measured against established therapies, 1,000-3,000 patients Parallel track |
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Mutation
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As nucleic acids replicate, mistakes occur. Changes in the genome are caled mutations.
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Field isolate
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virus strain that is isolated from natural host
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Wild Type
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the prevalent type of a virus in the host population before genetic manipulation or mutation; before lab
Original strain for study |
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Mutant
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has a genome mutation that varies from original
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Spontaneous mutation
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naturally happening without the use of known mutagen, low rate of mutation
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Induced mutation
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induced artificially
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Hemadsorption
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the adherence of red blood cells to other cells or surfaces; a process in which a substance or an agent, such as certain viruses and bacilli, adheres to the surface of an erythrocyte. The process occurs naturally, or it may be induced for laboratory identification of bacteriologic specimens.
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Complementation
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Genetic interaction of viral gene products. Two different viruses by themselves can't replicate if defective. Together they can produce viruses.
Ex. Polymerase from one virus, capsid from another assemble in a cell. |
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Recombination
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physical interaction of viral genomes, intramolecular or reassortment
Genomes interaction progeny can change genotype |
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Genetic Reactivation
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special case of recombination or reassortment. Marker rescue.
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Temperature sensitive
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Virsuses are temperature sensitive.
Permissive and non-permissive temperature |
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Defective viral genome
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Gene transfer and expression, regulatin of virus lethality, evolution of host and virus
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Defective viral genome types
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integrated defective, staellite virus, pseudovirons, conditional defective, DI particles
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Types of mutation
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Plaque morphology
Host range Temperature sensitive Cold sensitive Deletions Others |
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Pleiotropism
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single viral gene has effects on several viral properties.
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Satellite virus
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replication defective, require gene products of other virus, often show no homology to helper virus
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Defective Interfering Particles
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Subgenomic deletion mutants, helper virus dependent, helper and DI particle are homologous
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Therapeutic index
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is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death (in animal studies) or toxicity (in human studies).
Therapeutic ration = LD50/ED50 |
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Comparison of transcription in RNA viruses
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(+)sense RNA ->Translation->Viral protein
(-)sense RNA->virion transcriptase->mRNA->Translation->Viral protein Double sense RNA->virion transcriptase->mRNA->Translation->Viral protein |
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Picornaviridae Physical Characteristics
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-Naked virion
-Icosohedral -30nm in diameter -single-stranded (+) sense RNA -9 genus, indistinguishable in EM |
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Types of Picornaviridae
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Apthovirus->F&M
Caridovirus->encephalomyocarditis Enterovirus->polio, coxsackievirus, enterovirus, echovirus Hepatovirus->Hep A Parechovirus->Human parechovirus Rhinovirus->103 Rhinoviruses |
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Genome organiztion of Picornaviridae
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(+)sense ss RNA
Poly (AAA) tail at end VPg at end if AAA clipped off, not infectious |
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Capsid of Picornaviridae
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Icosohedral T=1
Proteins VP1,2,3,4 60 copies of VP4 per virion VP1 is antireceptor helps attachment |
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Attachment of Picornaviridae
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Electrostatic attachment
Specific receptors on cell surface |
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Penetration of Picornaviridae
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-Virion binds to receptor. As more receptors are recruited, the membrane is drawn around the particle.
-Receptor-mediated conformational change occurs, leading to the production of altered (A) particles. – VP4 is lost. |
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Translation of Picornaviridae
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• RNA can act as mRNA when it
enter the cell. • One ORF, translated as a single polyprotein. • Viral proteins derived by cleavage • Inefficient |
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Transcription of Picornaviridae
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• Replicative intermediates
Need replicase before transcription • 3 possible fates of +RNA: – Act as mRNA – Template for more -RNA – Genome for new virion |
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Assembly of Picornaviridae
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• Protomers self-assemble into pentamers.
• Pentamers assemble into empty procapsids. • After RNA is encapsidated, VPO cleaves and infectious virion is complete. |
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Effect of picornavirus infection on host cell
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• Susceptible cell contributes:
– Energy – Precursors for synthesis of viral components and cellular machinery – Receptors for infection – Membranes • Virus inhibits cellular RNA synthesis and protein synthesis |
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Inhibition of cellular translation by picornavirus
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• Inhibits 5
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Non-Polio Enteroviruses
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• Very common: 10-15 million symptomatic infections annually in the US.
• Pathogenesis – May play a role in autoimmune disease – Implicated in the etiology of diabetes – Important etiologic agent of viral myocarditis – Meningitis |
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Polio
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Attacks:
-muscles that straighten or bend hips -shoulders -straighten knee -lift foot -thumb muscles -back muscles -respiratory problems (iron lung) -Post polio (recovery to breath) |
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Hep A
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-Ingestion
-Replication in GI tract -Transported to liver (major replication site) -Shed in bile, transported to intestine -Shed in feces -Brief viremia -Cellular immune response |
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Caliciviridae
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-Icosohedral
-38nm + ssRNA -5' VPg and 3'poly(A) tail -Larger than picorna -1 coat protein -Subgenomic RNA -2 RNA transcripts, Genomic and subgenomic |
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Norovirus
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-90% of epidemic non-bacterial outbreaks of gastroenteritis around the world.
-Produces gastroenteritis -Incubation and disease very short |
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Hepatitis E
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Formerly Caliciviridae, no formal family assignment.
• Genome organization and size resemble calicivirus. • Causes epidemic water-borne hepatitis. • Found in Asia, Africa, southern Europe, Mexico • Disease is severe but mortality is low – Fatality rate higher in pregnant women. |
