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71 Cards in this Set
- Front
- Back
What are the 2 methods used to kill bacteria?
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1)Physical methods:
-heat -radiation -filtration 2)Chemical methods: -antiseptics/disinfectants -antibiotics |
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How does heat kill bacteria?
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-denatures proteins, DNA
-melts lipids -moist heat is better than dry heat b/c of faster penetration and better at protein denaturation *used because easy to perform* |
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What is pasteurization?
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-mild heat used to reduce the number of bacter
-doesn't kill all bacyteria present and doesn't kill lspores -delays spoilage because fewer bacteria in product |
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What is the safety margin used by canning industries?
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-canning companies use heating conditions designed to kill 10E12 spores
-therefore all pathogenic organisms are killed |
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What to forms of radiation are commonly used in sterilization?
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1)UV light: Cross links thymines in DNA, causes lethal mutations
-but has poor penetration props, good for surface only 2)Ionizing radiation(X and Gamma rays): -dislodges electrons -good penetration -commercial uses only |
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What is Filter Sterilization?
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-mechanical removal of bacteria (no kiling)
-used for heat sensitive liquids and gasses -used in pharmaceuticals, growth media additives, surgical gasses, beverages |
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What is the purpose of chemical control methods?
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-to reduce bacterial numbers to safe levels
-complete sterility may or may not be achieved -use of germicides -intended for use on surfaces |
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What are 2 types of germicides?
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1)Antiseptics: for use on biological surfaces (eg: skin)
2)Disinfectants: for use on inanimate surfaces |
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What are some general features of germicides?
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-more than 14000 different formulations from 300 diff chemicals
-act by denaturing proteins, nucleic acids or degrading lipids |
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What does the efficiency of germicides depend on?
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-conc used
-time of exposure -presence of organic material |
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Give 8 examples of disinfectants and antiseptics
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1)Phenols: -denatures proteins, disrupts membranes
-disinfectant (eg: lysol) 2)Alcohols: -dissolve lipids -anitseptic 3)Heavy Metals: -denatures proteins by binding -SH and -OH groups -antiseptic (eg:dandruff shampoo) 4)Peroxides: -oxidizes lipids, proteins -antiseptics (eg:anti acne cream) 5)Halogens: -denatures proteins & nucleic acids -antiseptic (eg:iodine) -disinfectant (eg:chlorine) 6)Quaternary ammonium compounds: -Cationic detergents based on NH4+, disrupts membranes -antiseptic (eg:mouthwashes) 7)Gaseous agents: -denatures proteins and DNA by crosslinking organic groups -disinfectant (eg:ethylene oxide, propylene oxide) 8)Chemicals as Preservatives: -used on food products to prevent microbial growth -disinfectants (eg:organic acids, nitrates) |
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What are some sources to antibiotics? 3 of them.
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-most are natural metabolic byproducts of soil microbes
-some are compounds synthesized in labs -some are semisynthetic (chemically converted natural compounds to form a new antibiotic) |
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What are 3 general characteritics of antibiotics?
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1)Selective Toxicity: -must kill bacteria without harming host
-expressed as therapeutic index (TI) 2)Cidal vs Static Effect: -Bacteriocidal=kills bacteria -Bacteriostatic=inhibits growth 3)Spectrum of Activity: -narrow vs broad spectrum |
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What is the therapeutic index(TI)?
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Dose which is toxic to host/Dose required to kill bacteria
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What are the 5 ways that antibiotics work?
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1)Block DNA/RNA Synthesis
-eg rigamycin 2)Block protein synthesis -eg erythromycin 3)Competitive metabolic inhibitors -eg sulfonilamide 4)Disrupts cell membrane function -eg polymyxin 5)Blocks peptidoglycan synthesis -eg penicillin |
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What are the principles of combination antibiotics? 2 of them
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-wants to avoid antagonism (one drug preventing the action of a second drug)
-wants to achieve synergism (enhanced effects vs either drug alone |
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What are some side effects to antibiotic use?
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1)Toxic to host
2)Allergic reactions (eg: penicillin) 3)Disruption of normal flora (eg: messes up gut boys and causes diarrhea) |
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What is bacterial antibiotic resistance?
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-when a normally senstive bacteria is no longer affected by antibiotic
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How do we know if bacteria are resistant?
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1)in vivo- patient is unresponsive to antibiotic therapy
2)in vitro- labs test for growth of bacteria in presence of the antibiotic -determines: how resistant, correct antibiotic and proper dosage |
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What are 2 ways of measuring resistance?
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1)Disk Diffusion Method:
-put disc of antibiotic on infected plate, measure growth of inhibition 2)Tube Dilution Method -if growth occurs at high antibiotic concentration, then bacteria is resistant -can find Minimal Inhibitory Conc (prevent growth) -can find Minimal Bactericidal Conc (kills bacteria) |
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What are 3 mechanisms used to become resistant to antibiotic?
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1)Direct inactivation of antibiotic
-bacteria produces enzymes which break down antibiotic 2)Prevent uptake or promote excretion of anitbiotic 3)Alteration of antibiotic target: a)overproduction of target overwhemls antibiotic b)mutated target no longer recognized by antibiotic |
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How is resistance acquired by bacteria? 2 of them
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1)Spontaneous mutation in DNA (gives an altered target)
-low freq 2)Acquire new resistance gene (gene for inactivating enzyme) -plasmids may carry multiple resistance genes, passed on from bac. to bac. |
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What factors lead to the spread of resistance? 3 of them
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1)Clinical overuse of antibiotics
2)Lack of patient compliance (ie:failure to take drug as prescribed). Therefore not all bac. killed and survivors develop reistance. 3)Widespread nontherapeutic use of antibiotics: -gut basteria constantly exposed to antibiotics -develops reservoir of resistant bacteria **Key Points: -if antibiotics are continously in enviro, then bacteria is constantly exposed, therefor continual selective pressure for resistant strains** |
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What would you do to limit the developement of resistance? 5 of them
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-promote responsible clinical use of antibiotics
-restrict use of some antibiotics in human and animal health -rotate use of different types of antibiotics -use combo antibiotics to slow devel of resistance -better public education in responsible antibiotic use |
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What are some new sources of antibiotics?
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1)New soil, water bacteria and fungi continuously being screend to find undiscovered antibiotic
2)Rejuvenate existing antibiotics: may be lethal to bac again 3)Novel nonmicrobial sources of antibiotics 4)Rational drug design -pick specific bacteria and target it -make a chem which kills it -takes about 10 years to do |
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What is a virus?
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-a non cellular infectious agent
-nucleic acid usually surrounded by a protein coat -metabolically inert -reproduce only within a living host cell |
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What are some key ways in which viruses differ from liveing cells? 5 of them
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-much smaller in size
-simple (non-cellular) structure and organization -contains either DNA or RNA, but never both -not capable of independent reproduction -2 distinct phases in life cycle (depends on whether inside or outside of the cell) |
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What is host range?
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-range of organism used by virus as host
-viruses have host specificity -host specificity determined by receptors on host cell and presence of suitable metabolic machinery in host cell |
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What is the structure of viruses?
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a)has many types of nucleic acid
-ds DNA -ss DNA -ds RNA -ss RNA ('plus' orientation = mRNA) -ss RNA ('minus' orientation = anit mRNA) ***nucelic acid can be circular or linear virus will ONLY HAVE ONE TYPE of nucleic acid*** b)Has 3 types of protein coats: 1-Helical 2-Icosahedral 3-Complex c)Presence or absence of envelope |
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What is a capsomer?
What is a capsid? |
-indiviual protein subunits which comince to make a complete shell for viruses
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What are the 3 basic shapes of protein coats for viruses?
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1)Helical: capsomeres coiled in rod shaped spiral form
2)Icosahedral: capsomers in a geometric conficuration of 12 corners and 20 faces ("geodesic dome") 3)Complex: helical 'tail' attached to icosahedral head (eg: bacteriophage) |
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What's the difference between a naked and and enveloped virus?
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Naked virus:
-NA core enclosed only by capsid -capsid may contain spikes (helps bind to receptors) Enveloped virus: -core + capsid + outer lipid envelope -spikes associated with envelope -parts of envelope are teaken from host cell plasma membrane as virus exits from host cell |
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What 3 factors are taken into account when classifying viruses?
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1)Type of nucleic acid
2)Type of protein coat 3)Presence or absence of envelope |
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Go over the life cycle of viruses.
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1)Adsorption: virion attaches to host cell
2)Penetration: intact virion (or it's NA) enters the cell 3)Uncoating: release of viral NA from capsid (skipped if NA alone penetrates) 4)Gene Expression: viral genes expressed to produce more viral NA and viral proteins 5)Assembly: new intact viruses assemble inside host cell 6)Release: virus particles exit host cell |
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What is a virion?
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-a virus outside of the host cell
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What is Lytic infection?
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-lysis of bacterial host cell and release of new virion
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What is lysogenic infection?
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After attachment and penetration:
-vireus genome recombines into bacterial chromosome (prophage) -phage genome replicates as part of chromosome -all bacterial daughter cells carry virus in prophage state **prophage may bust out of chromosome and enter lytic pathway** |
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What are the 2 possible outcomes of bacteriophage infection?
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1)Lytic infection
2)Lysogenic infection |
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T/F Some viruses can act as antibiotics.
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T
-viruses attack bacteria -problem is controlling the virus afterwards |
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What steps are involved in adsorption?
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-requires receptors on eucaryotic cell membrane
-receptors are recognized by viral spikes (proteins) -spike+receptor interaction determines virus host rand and tissue specifictiy -blocking receptor+spike interaction may prevent infection (eg: antibodies) |
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What 3 mechanisms are involved in Penetration?
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1)Direct penetration through host membrane by naked viruses
2)Fusion of virion envelope with host cell, parts of viral envelope left behind by enveloped viruses 3)Endocytosis: uses existing phagocytic mech of cell (enveloped viruses) |
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What steps are involved in uncoating?
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-exposes virus nucleic acid to hosts biochemical machinery
-can occur during penetration or after penetration -usually due to host hydrolytic enzymes which degrade capsid |
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What steps are involved in gene expression?
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-viral nucleic acid is transcribed, translated, replicated
-usually completely dependent on host cell enzymes -can be very complex, depending on type of NA in virion |
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What is the difference between 'early' and 'late' genes of the viral genome?
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-Early genes-> transcribed immediately after entry into cell
-Late genes-> transcribed only after new viral RNA polymer is made |
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What steps are involved in assembly?
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-building of new intact virus from component parts
-process varies depending on type of virus >some spontaneous self assembly of capsid proteins >sometimes requires enzymes from virus and/or host >may occur in cytoplasm or nucleus -poorly understood process for animal viruses |
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What steps are involved in release?
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A)For Naked Viruses:
-virus particles assembled and accumulate in cytoplasm -host cells biosynthesis stops -host cells die and lyses -virions are released B)For Enveloped Viruses: -virus glycoproteins are inserted into the inside of host cell membrane -assembled virus capsid begins to bud out through the membrane -envelope aquired while budding *Budding may or may not kill the cell *if host cell survives, may continue to shed virus *some viral protinds may be left behind on cell surface, cell is killed by immune system |
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What are 4 possible outcomes of viral infections?
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1)Lytic Infection:
-host cell is killed as virions are released 2)Peresistent (Chronic) Infection: -host cell survives -virus shed for a long period of time -infectious virions constantly present in patient 3)Latent Infection: -host cell survives -viral genome replicates as part of host chromosome -very limited ecpression of viral genes -no mature infectious virus released -viral gene expression may be triggered at future time 4)Host Cell Transformation: -formation of cancerous host cells by tumor viruses |
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What are 5 problems with antiviral agents?
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1) Side effect & toxicity to host cells: -viral life cycle is closely linked to that of the host cell
-it is hard to affect one without affecting the other -many viruses still cannot be treated with anti-viral agents 2)Latent viruses may not be susceptible 3)Many viruses have long incubation periods 4)Resistance to some antivirals are developing 5)Developement of new agents is difficult |
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What are prions?
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-infectious agents consisting only of protein
-an abnormally folded variant of a natural protein found in neurons -causes slow diseases (ie: mad cow) |
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Whats the difference between PrP(C) and PrP(SC)?
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-PrP(C) is a good prion (protease sensitive, does not aggregate)
-PrP(SC) is a bad prion (protease resistant, readily aggregates). Becomes spongy masses and clogs neurological system (causes mad cow) -PrP(SC) can convert PrP(C) to PrP(SC) if they come in direct contact with eachother |
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What are some problems faced when diagnosing viral infections?
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-symptoms of some viral disease mimic other microgbial diseases
-different types of viruses may produce similar symptoms -diagnostic methods based on growth are more difficult for viruses than bac. |
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What is serology?
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-looks for antibodies produced against viruses in patients blood
-used to diagnose viral infection -can't tell diff b/w past and current infections -might take long for antibodies to be made |
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What 3 methods are used to diagnose viral infections?
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1)Serology
2)Look for virus infected cells in host. Done adding antibodies tagged with fluorescent dye 3)Try to grow and identify virus directly from host. -Requires use of Tissue Culture Cells (TCC) -Add virus to TCC and allow infection -look microscopically for ctyopathic effect on cells -virus will cause change in morphology >cell lysis >rounding, fusing of cells >inclusions inside cells *slow process* |
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How do viruses cause symptoms of disease? 4 of them.
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1)Virus replication leads to host cell lysis
2)Virus infection alters host cell metabolism 3)Viral glycoproteins (spikes) insert into host cell membrane 4)Production of 'virokines' during virus infection |
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T/F Viruses often stay at the site of first contact with the host.
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F
-Viruses spread via blood or lymphatic system -may infect cells at other sites as long as suitable cell receptors are present |
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T/F Viruses can infect almost every body organ
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T
-these bastards are versitile |
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What viruses are responsible for causing diarrhea?
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-Enteric viruses (eg: Rotavirus, Norwalk virus, Adenovirus, Astrovirus)
-infected due to ingestion of infected food and water |
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What is Rotavirus?
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-naked, dsRNA, double layered capsid (acid resistant)
-infects villi -leads to lysis which causes fever, vominting, diarrhea -up to 10E9 virion/ml of feces released -symptoms last approx 1wk -affects young kids, 90% of adults have antibodies against rotavirus |
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What is Hepatits C Virus (HCV)?
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-a blood borne virus
-inflames the liver -causes: weight loss, fever, jaundice, fatigue, muscle and joint pain, loss of lever function, death -Enveloped, ssRNA -fast replication -infected by blood or body fluids only!!! -20% of acute patients eliminate virus w/o further probs with treatment -80% acute of patients enter chronic state (infection persists for >6mths) |
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What is Herpes Simplex Virus (HSV)?
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-large, enveloped, dsDNA virus
-a nervous system virus -has a huge host range -infection begins at breaks in mucosal surfaces or skin (ie: needs contact with infected animal) -HSV enters epithelial cells (causing fluid filled blisters) -HSV may spread to neurons causing Latent infections: >analogous to 'prophage' state >little viral gene expression >no damage to host cell |
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What are the 5 types of Herpes infections?
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1)Oral herpes (cold sores) - HSV-1
2)Herpes keratitis - infects eyes 3)Herpes whitlow - fingers 4)Genital Herpes - (HSV-2) -point of entry is dink or vagi >vesicular lesions occur (itch, pain, discharge) >first infection, get flu like symptoms >virus becomes latent, can be reactivated whenever 5)Herpes encephalitis - migration of HSV to brain. F's up behavior, seizure, fever, nausea |
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How do you control Herpes Simplex Virus (HSV)?
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-acyclovir: not a cure, shortens duration of active leions
-avoid contact with active lesions -can kill with a good soap wash. Kills lipid envelope |
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What is West Nile Virus(WNV)?
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-a virus of the nervous system
-enveloped, ssRNA -transmitted by mosquitoes, breast milk, organ transplants, blood transfusion -may cause fever, headache, rash, swollen glands -lasts 3 to 4 days, no long term effects -patients >50yrs are at risk of developing encephalitis >inflames brain >headache, high fever, disorientation, stiff neck, muscle aches, paralysis, convulsions >symptoms last for weeks then subside *no real vaccine |
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What is the influenze virus?
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-a respiratory tract virus
-enveloped, ssRNA, segmented RNA(8 pieces) 2 types of spike proteins on envelope 1)Neuraminidase(N): -degrades mucus that lines epithelial cells or resp. tract -required for release of mature virion from host cell 2)Hemagglutinin(H): -for attachment |
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Go over the life cycle of the influenza virus.
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-attaches to epithelial cell receptos
-virion envelope fuses with host membrane -releases ssRNA into cytoplasm and migrates to the nucleus -assembly of mature virion in cytoplasm -released by budding **transmitted by aerosols or hand to nose contact** **damages host cells and kills them** |
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What are the 3 types of influenza virus?
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Type A:
-most common -broad host range (humans, birds, pigs) -can cause pandemics(world wide spread) Type B,C: -infect only humans -don't cause pandemics(small outbreaks) -usually milder symptoms |
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How do different flu strains arise? 2 mechanisms.
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1)Antigenic Drift:
-spontaneous mutations in H or N genes which give rise to minor changes in H or N proteins 2)Antigenic Shift: -completely new H and/or N protein acquired from another flu virus -possible becusae of segmented genome |
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What is the ebola virus?
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-only found naturally on African continent
-Enveloped; 1 ssRNA with 12 genes -broad host range -causes viral hemorrhagic fever -virion enters directly into blood or inhaled -tend to hang out in blood, lungs, and nasal secretion *2 days of infection: high fever, headache, fatigue, bloody diarrhea *7-10 days of infection: mucosal bleeding, circ system collapse, shock, blindness, death |
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What do we know about Ebola's transmission? 3 of them
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1)Zoonotic disease:
-animal to human transmission 2)Human to human transmission: -via physical contact with secretions, blood of patients -airborne spread possible but rare 3)International outbreaks are possible (ie: beyond Africa) |
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What hypothesis were made regarding the genesis of viruses? 3 of them.
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1)Retrograde evolution:
-cells which have continually lost funstion so as to become completely dependent on another host 2)Cellular origin -combos of cellula macromolecules (protein, NA) that gained ability to self assemble and replicate 3)Parallel evolution of cells and viruses when life first began **No strong evidence for any of the above** |
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Why are viruses important from a scientific viewpoint? 3 reasons
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-models for gene organization and expression
-used as vectors for introducing new genes into animal cells -used as possible agents of human gene evolution |