传染病学英文版课件：Influenza (the flu)

Influenza(theflu)

Acoldisamilderrespiratoryillnessthantheflu.Whilecoldsymptomscanmakeyou

feelbadforafewdays.Flusymptoms

canmakeyoufeelquiteillforafewdaystoweeks.Coldsymptomsusuallybeginwitha

sorethroat,whichusuallygoesawayafteradayortwo.Nasalsymptoms,runnynose,andcongestionfollow,alongwitha

cough

bythefourthandfifthdays.Feverisuncommoninadults,butaslightfeverispossible.Childrenaremorelikelytohaveafeverwithacold.Withcoldsymptoms,yournoseteemswithwaterynasalsecretionsforthefirstfewdays.Later,thesebecomethickeranddarker.Whetherapersonhastypicalseasonalfluorswineflu,thesymptomsseemtobequitesimilar.Flusymptomsareusuallymoreseverethancoldsymptomsandcomeonquickly.Symptomsofswinefluandseasonalfluincludesorethroat,fever,

headache,muscleachesandsoreness,congestion,andcough.Swinefluinparticularisalsoassociatedwithvomitinganddiarrhea.DifferenceBetweenColdorFLUInfluenza(theflu)isacontagiousrespiratoryillnesscausedbyinfluenzaviruses.Itcancausemildtosevereillness,andattimescanleadtodeath.Thebestwaytopreventseasonalfluisbygettingaseasonalfluvaccinationeachyear.

Invirusclassification

influenzavirusesare

RNAviruses

thatmakeupthreeofthefive

generaofthefamilyOrthomyxoviridae.

InfluenzavirusA

InfluenzavirusB

InfluenzavirusC

Influenza(theflu)InfluenzaAvirusThetypeAvirusesarethemostvirulenthumanpathogensamongthethreeinfluenzatypesandcausethemostseveredisease.TypeAfluorinfluenzaAvirusesarecapableofinfectingpeopleaswellasanimals.WildaquaticbirdsarethenaturalhostsforalargevarietyofinfluenzaA.TheinfluenzaAviruscanbesubdividedintodifferent

serotypes

basedon

theantibody

responsetotheseviruses.Theserotypesthathavebeenconfirmedinhumans,orderedbythenumberofknownhumanpandemicdeaths,are:H1N1,whichcaused

Spanishflu

in1918,andthe

2009flupandemic

H2N2,whichcaused

AsianFlu

in1957H3N2,whichcaused

HongKongFlu

in1968

H5N1,acurrent

pandemic

threatH7N7,whichhasunusual

zoonotic

potentialH1N2,endemicinhumansandpigsH9N2

H7N2

H7N3

H10N7

InfluenzaBvirusInfluenzaBalmostexclusivelyinfectshumansandislesscommonthaninfluenzaA.Thistypeofinfluenzamutatesatarate2–3timeslowerthantypeA.Thisreducedrateofantigenicchange,combinedwithitslimitedhostrangeensuresthatpandemicsofinfluenzaBdonot

occur.InfluenzavirusCInfluenzaCvirus,whichinfectshumans,dogsandpigs,sometimescausingbothsevereillnessandlocalepidemics.However,influenzaCislesscommonthantheothertypesandusuallyonlycausesmilddiseaseinchildren.

InfluenzavirusesA,BandCareverysimilarinoverallstructure.Thevirusparticleis80–120

nanometres

indiameterandusuallyroughlyspherical,althoughfilamentousformscanoccur.ThesefilamentousformsaremorecommonininfluenzaC,whichcanformcordlikestructuresupto

500

micrometres

longonthesurfacesofinfectedcells.

StructureTheviralparticlesofallinfluenzaVirusesaresimilarincomposition.Thesearemadeofaviralenvelopecontainingtwomaintypesofglycoproteins,wrappedaroundacentralcore.

ThecentralcorecontainstheviralRNA

genomeandotherviralproteinsthatpackageandprotectthisRNA.RNAtendstobesinglestrandedbutinspecialcasesitisdouble.Unusuallyforavirus,itsgenomeisnotasinglepieceofnucleicacid;instead,itcontainssevenoreightpiecesofsegmentednegative-senseRNA,eachpieceofRNAcontainseitheroneortwogenes.Forexample,theinfluenzaAgenomecontains11genesoneightpiecesofRNA,encodingfor11proteins:hemagglutinin(HA),neuraminidase(NA),nucleoprotein(NP),M1,M2,NS1,NS2(NEP),PA,PB1,PB1-F2andPB2Hemagglutinin(HA)andneuraminidase(NA)arethetwolargeglycoproteinsontheoutsideoftheviralparticles.HAisalectinthatmediatesbindingofthevirustotargetcellsandentryoftheviralgenomeintothetargetcell,whileNAisinvolvedinthereleaseofprogenyvirusfrominfectedcells,bycleavingsugarsthatbindthematureviralparticles.Thus,theseproteinsaretargetsforantiviraldrugs.Furthermore,theyareantigenstowhichantibodiescanberaised.

Hemagglutinin&NeuraminidaseInfluenzaAvirusesareclassifiedintosubtypesbasedonantibodyresponsestoHAandNA.ThesedifferenttypesofHAandNAformthebasisoftheHandNdistinctionsin,forexample,H5N1.Thereare16Hand9Nsubtypesknown,butonlyH1,2and3,andN1and2arecommonlyfoundinhumans.ThemostprevalenthumanfluvirusesareH1N1andH3N2.AllofthehumanversionsofH1N1andH3N2caneasilytransmittedfrompersontopersonbecausetheH1andH3proteinsrecognizehumancellreceptors,makingiteasyforthemtosplitintohealthycells.SeasonalFluSeasonalfluisthetermusedtorefertothefluoutbreaksthatoccuryearly,mainlyinthelatefallandwinter.PandemicFluPandemicflureferstoparticularlyvirulentstrainsoffluthatspreadrapidlyfrompersontopersontocreateaworld-wideepidemic(pandemic).Avian(Bird)FluThefluvirusoccursinwildaquaticbirdssuchasducksandshorebirds.Itdoesnotnormallyspreadfrombirdstohumans.However,pigscanbeinfectedbybirdinfluenza(aswellasbytheformofinfluenzathataffectshumans)andcanpassontheflutohumans.In1997,itwasdiscoveredthatavirulentbirdinfluenzahadskippedthepigstepandhadinfectedhumansdirectly,causinganumberofdeathsinAsia.

Mostflusymptomsgraduallyimproveovertwotofivedays,butit'snotuncommontofeelrundownforaweekormore.Acommoncomplicationofthefluispneumonia,particularlyintheyoung,elderly,orpeoplewithlungorheartproblems.Ifyounoticeshortnessofbreath,youshouldletyourdoctorknow.Anothercommonsignofpneumoniaisfeverthatcomesbackafterhavingbeengoneforadayortwo.Earinfections,

Sinusinfections,Dehydration,andWorseningofchronicmedicalconditions,suchascongestiveheartfailure,asthma,ordiabetes.

ComplicationsofFlu

Influenzaspreadsaroundtheworldinseasonalepidemics,resultinginthedeathsofhundredsofthousandsannually—millionsinpandemicyears.Threeinfluenza

pandemicsoccurredinthe20thcenturyandkilledtensofmillionsofpeople,witheachofthesepandemicsbeingcausedbytheappearanceofanewstrainofthevirusin

humans.Often,thesenewstrainsappearwhenanexistingfluvirusspreadstohumansfromotheranimalspecies,orwhenanexistinghumanstrainpicksupnewgenesfromavirusthatusuallyinfectsbirdsorpigs.AnavianstrainnamedH5N1raisedtheconcernofanewinfluenzapandemic,afteritemergedinAsiainthe1990s,butithasnotevolvedtoaformthatspreadseasilybetweenpeople.InApril2009anovelflustrainevolvedthatcombinedgenesfromhuman,pig,andbirdflu,initiallydubbed"swineflu"andalsoknownasinfluenzaA/H1N1,emergedinMexico,theUnitedStates,andseveralothernations.TheWorldHealthOrganizationofficiallydeclaredtheoutbreaktobea"pandemic"onJune11,2009.TheWHO'sdeclarationofapandemiclevel6wasanindicationofspread,notseverity.InfluenzaPandemic

BirdFluFifteensubtypesofinfluenzavirusareknowntoinfectbirds,thusprovidinganextensivereservoirofinfluenzavirusespotentiallycirculatinginbirdpopulations.Todate,alloutbreaksofthehighlypathogenicformhavebeencausedbyinfluenzaAvirusesofsubtypesH5andH7.ThestrainofavianfluknownasH5N1hasbeenbehindmostrecentoutbreaksofdeadlyavianfluandhasalsobeenresponsiblefortherecenthumandeathsreportedinasia,buttherearethreeprominentsubtypesofavianinfluenzavirusandamongthethreesubtypes,influenzaAH5,AH7andAH9,thereareseveralstrainswithvaryingdegreesofstrength.Lowpathogenicity(LPAI)-usuallyonlycausingmildrespiratorydiseaseindomesticpoultry

.Highpathogenicity(HPAI)-

themorevirulenttypeformerlyknownasfowlplaguewhichoftenresultsinuptoa100%flockmortality.

Thisreassortmentprocess,knownasantigenic“shift”,resultsinanovelsubtypedifferentfrombothparentviruses.Aspopulationswillhavenoimmunitytothenewsubtype,andasnoexistingvaccinescanconferprotection,antigenicshifthashistoricallyresultedinhighlylethalpandemics..Conditionsfavorablefortheemergenceofantigenicshifthavelongbeenthoughttoinvolvehumanslivingincloseproximitytodomesticpoultryandpigs.Becausepigsaresusceptibletoinfectionwithbothavianandmammalianviruses,includinghumanstrains,theycanserveasa“mixingvessel”forthescramblingofgeneticmaterialfromhumanandavianviruses,resultingintheemergenceofanovelsubtype.Antigenic“Shift”

InfectionControlThesinglebestwaytopreventseasonalfluistogetaseasonalfluvaccinationeachyear.Therearetwotypesoffluvaccines:The"flushot":aninactivatedvaccine(containingkilledvirus)thatisgivenwithaneedle.Theseasonalflushotisapprovedforuseinpeople6monthsofageandolder,includinghealthypeopleandpeoplewithchronicmedicalconditions.Thenasal-sprayfluvaccine:avaccinemadewithlive,weakenedfluvirusesthatdonotcausetheflu(sometimescalledLAIVfor"LiveAttenuatedInfluenzaVaccine").LAIVisapprovedforuseinhealthy*people2-49yearsofagewhoarenotpregnant.Abouttwoweeksaftervaccination,antibodiesdevelopthatprotectagainstinfluenzavirusinfection.Fluvaccineswillnotprotectagainstflu-likeillnessescausedbynon-influenzaviruses.Aseasonalfluvaccinewillnotprotectyouagainstthenew2009H1N1flu.AvaccineagainstthenewH1N1fluisbeingproduced.PreventingSeasonalFlu:GetVaccinated

VaccinationshavebeenproducedtohelpfightthespreadofinfluenzaA,butbecausetherearesomanystrainsofthevirus,vaccinationsarenotalwayseffectiveorreliable.????

Sideeffectsareexpectedtobesimilartothoseobservedwithseasonalinfluenzavaccines.Commonsideeffectsincludelocalreactionsattheinjectionsite(soreness,swelling,redness)andpossiblysomesystemicreactions(fever,headache,muscleorjointaches).Inalmostallvaccinerecipients,thesesymptomsaremild,self-limitedandlast1-2days.

However,evenverylargeclinicaltrialswillnotbeabletoidentifypossiblerareeventsthatcanoccurwhenpandemicvaccinesareadministeredtomanymillionsofpeople.Furthertestingofsafetyandeffectivenesswillneedtotakeplaceafteradministrationofthevaccine.

/csr/disease/swinefluVaccinesafety

Whathappenedduringthelastswineflupandemicin1976?The1976SwineFluVaccinecausedGuillain-BarréSyndrome;acripplingparalysisthatcanbefatalifnottreatedquickly.MedianowreportingthattherewasanunprovenlinktoGBS,BUTtheactingheadoftheCDC'sImmunizationSafetyOffice,Dr.JohnIskandersaidinFeb.2008"Aprovenassociationbetweenthe1976-1977swineinfluenzavaccineandGuillain-Barrésyndrome.

/Papers/69348/Swine_Flu_The_virus_and_the_mass_vaccination_campaign.ppt,Arethe