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Marburg and Ebola viruses

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PRINTED FROM OXFORD MEDICINE ONLINE (www.oxfordmedicine.com). (c) Oxford University Press, 2014. All RightsReserved. Under the terms of the l icence agreement, an individual user may print out a PDF of a single chapter of a title in OxfordMedicine Online for personal use (for details see Privacy Policy).date: 14 October 2014

Publisher: OxfordUniversityPress PrintPublicationDate: Jul2011PrintISBN-13: 9780198570028 Publishedonline: Jul2011DOI: 10.1093/med/9780198570028.001.0001

Chapter: MarburgandEbolavirusesAuthor(s): G.LloydDOI: 10.1093/med/9780198570028.003.0038

OxfordMedicine

OxfordTextbookofZoonoses:Biology,ClinicalPractice,andPublicHealthControl(2ed.)EditedbyS.R.Palmer,LordSoulsby,PaulTorgerson,andDavidW.G.Brown

MarburgandEbolaviruses

Summary

MarburgandEbolavirusescausesevereandoftenfatalhaemorrhagicdiseaseinhumansandnon-humanprimates.TheyarethetwoestablishedmembersofthefamilyFiloviridaeandhaveadistinctivefilamentousandirregularmorphologywithagenomeconsistingofaverylarge(about19kb)single-strandedRNAofnegativepolarity.FeaturesoftheirorganizationandstructureatthemolecularlevelhaveledtotheirinclusioninthetaxonomicorderMononegavirales,togetherwiththeParamyxovirusesandtheRhabdoviruses.

Fromitsoriginaldescriptionin1967to2009,therehavebeeneightreportedoutbreaksofhumanMarburgvirusinfection.ThefirstbeingthreesimultaneousoutbreaksthatoccurredinEuropeatMarburg,Frankfurt,andBelgrade,followingtheimportationofinfectedAfricangreenmonkeys(Ceropithecusaethiops)fromUganda.TheremainingoutbreaksoccurredinSouthAfrica1975;Kenya1980and1987;DemocraticRepublicofCongo(DRC)(1988–2000);Angola(2004–5)andUganda(2007and2008).Theseeightepisodesinvolved449caseswith369deaths,anoverallfatalityrateof82.3%.Allthedeathstodatehaveoccurredintheprimarycases.

Between1976and2009outbreaksofhumanEbolahaemorrhagicfeverhavebeenidentifiedinZaire(1976,1977,1995,2001–2,2003and2007);Sudan(1976,1979and2004);Uganda(2000–1and2007–8);Kenya(1980);Côted’Ivoire(1994and1995);andtheGabon(1996and1997).Allagegroupsandsexeswereaffected.Inaddition,alaboratory-derivedinfectionoccurredduringthestudiesofthe1976ZaireandSudanepidemic.Thereisnoknownendemicincidenceofthediseaseandthemortalityratesarebasedonthelimitednumbersofepidemicsidentified.Thishasinvolved2,292-recordedcaseswith1,524deaths,anoverallcasefatalityrateof66.5%.

AnewstrainofEbolavirusnamedRestonwasisolatedfromanepizooticofdyingcynomolgusmonkeysshippedtotheUSA(1989,1990)andItaly(1992)fromthePhilippines.ThevirusprovedantigenicallyandgeneticallydistinctfromtheAfricanEbolaviruses.HumaninfectionsdocumentedduringtheUSAepizooticprovedasymptomatic.TherewasnoevidenceofanepidemiologicallinkwithAfrica.Therefore,unlikeitsAfricancounterpartsRestonEbolaVirushasproventodatetobenon-pathogenicinhumans.Thehighmortalityamongmonkeysmakesthemanunlikelynaturalreservoirs.However,sixoutof141slaughterhouseworkersstudiedinthePhilippines,whohaddailycontactwithEbolaseropositivepigs,hadantibodiesagainstRestonebolavirus.ThismarksthefirsttimethatRestonebolavirushasbeenfoundinpigs


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andthepossibilityofEbolatransmissiontohumansfrompigstohumans,hasoccurred(Barrette2009;WorldHealthOrganization(WHO)2009).

InAfrica,thetransmissionofhaemorrhagicfevercausedbyEbolaandMarburghasbeenassociatedwiththereuseofunsterileneedlesandsyringes,withtheprovisionofpatientcarewithoutappropriatebarrierprecautionspreventingexposuretovirus-containingbloodandotherbodyfluidsandpreparingbodiesforfuneralsandburial.Inaddition,thekillingandpreparingofnon-humanprimatesforfoodwasconsideredthesourceofSOMPoutbreaks.Epidemiologicalstudiesinhumansindicatethattheairborneroutedoesnotreadilytransmitinfectionfrompersontoperson.Bycontrast,studiesofEbolaandMarburgvirusinfectionsinnon-humanprimateshavesuggestedpossibleairbornespreadamongthesespecies.Theriskofperson-to-persontransmissionishighestduringthelaterstagesofillness.Studiesofindividualswhoareincontactwithaninfectedpatientduringtheincubationperiodindicatethatinfectionriskislow.

AsthenaturalhistoryandreservoiroftheFilovirusesareunknown,therearenospecificprecautionsforavoidinginfectionfromthenaturalenvironment.Non-humanprimatesarenotconsideredthenaturalreservoirofFilovirusesdespitebeingthesourceofMarburgvirusintroducedintoEuropeandEbolavirusesintroducedintotheUSAandItaly.Theprecautionaryquarantiningofnon-humanprimatesimportedfromAfricaandAsiaforaminimumofsixweeksreducesthepossibilityofintroducingaFilovirusinfection.Recently,extensivestudiesundertakentodeterminethereservoirofFiloviruseshaveidentifiedincommonspeciesoffruitbat(Rousettusaegyptiacus)asapotentialcandidate(Swanepoel1996;Towner2007;Pourrut2009).

SincetherearenolicensedvaccinesorspecificantiviraldrugsforthetreatmentofFilovirusinfections,earlyidentificationofinfectedpatientsoranimalsisessential.Preventionstrategiesreducingtheriskoftransmissioninendemicandnon-endemicareasrelyontheintroductionofstrictisolationoffebrilepatientsandrigoroususeofbarrierprecautions.Consequently,manyinstitutionsandexpertsconsiderFilovirusespotentialbiologicalweapons(Borro2002).Filoviruspublichealthandbiodefenceresearchrequiretheuseofmaximum-containmentlaboratoryfacilitieswhereFilovirusesarehandledunderbiosafety-level(BSL)-4containmenttoprotectlaboratoryworkersfrominfection.Thereareonlyafewsuchfacilitiesthatexistworldwide.

History

Filovirusinfectionswereunknownuntil1967,when31humancasesofanacutehaemorrhagicfeveroccurredsimultaneouslyinMarburgandFrankfurt,FederalRepublicofGermany,andBelgrade,formerYugoslavia(Martini1969).Laboratoryworkers,medicalpersonnel,animalcarepersonnelandtheirrelativeswereinfected,sevenofwhomdied.Theprimarycasesoccurredthroughcontactwithkidneytissue,blood,andcellculturesderivedfromVervetorAfricangreenmonkeys(Ceropithecusaethiops)importedfromUganda.Thevirusisolatedfrompatient’sbloodandtissuewasmorphologicallyuniquewhenobservedbyelectronmicroscopy(seeFig.31.1a)andantigenicallyunrelatedtoanyknownmammalianpathogen.ThisviralagentwasnamedMarburgvirus(MBG)afterthecityofMarburg,wheremostofthecasesandinitialworkoccurred.During1975(Zimbabwe),1980and1987(Kenya)thereweresporadicfatalcasesidentifiedprimarilyamongsttourists.TheKenyancaseshadincludedvisitstobatinfestedKitumcavesinKenya’sMountElgonNationalPark(Gearetal.1975;Smithetal.1982;Teepeetal.1983;Johnsonetal.1996)(Table31.1).Apartfromthe1987case,secondaryinfectionsprovedarisktohealthcareworkers.Furtherepidemiologicalinvestigationsintheseareashasrevealednoinformationontheoriginoftheseinfectionsoccurred.

Fig.31.1


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(a)Electronmicrograph,showingfilamentousformsofEbola(Reston)virus(×18360).(b)Ebola(Sudan)virusthinsection,showingvirionsextrudingfromcellsintoextracellularspaces(×14040).

CourtesyofB.Dowsett

Table31.1HumanpathogensintheorderMononegavirales

Family Subfamily Genus Humanpathogens

Rhabdoviridae

Lyssaviru Rabiesvirus

Filoviridae

Marburgvirus Marburgvirus

Ebolavirus Ebolavirus

Paramyxoviridae

Paramyxovirinae

Rubulavirus Mumpsvirus,Parainfluenzavirus2,4

Respirovirus Parainfluenzavirus1,3

Henipavirus Hendravirus,Nipahvirus

Morbillivirus Measlesvirus

Rubulavirus Mumpsvirus,Parainfluenzavirus2,4

Pneumovirinae

Pneumovirus Respiratorysyncytialvirus

Metaneumovirus Humanmetapneumovirus

Betweenlate1998and2000inDemocraticRepublicoftheCongothefirstlargeoutbreakofthisdiseaseundernaturalconditionsoccurred,whichinvolved154cases,ofwhich128werefatal,representingacasefatalityrateof83%.ThemajorityofcasesoccurredinyoungmaleworkersatagoldmineinDurba,inthenortheasternpartofthecountry,whichprovedtobetheepicentreoftheoutbreak.CasesspreadtotheneighbouringvillageofWaste.Familymembersinvolvedintheclosecareofpatientsaccountedforsomecases,butsecondarytransmissionappearedtoberare.

ThelargestMarburgoutbreakinhistoryoccurredbetween2004and2005,inAngola.ItwasbelievedtohavestartedinUigeProvinceinOctober2004thatresultedin252cases,with227deaths(CFR88%)countrywidebyJuly2005.AllcasesdetectedinotherprovinceswerelinkedtotheoutbreakinUige(Towers2006).

FromJunetoAugust2007,threeconfirmedcasesoccurredamongstmineworkersworkinginKamwenge,westernUgandawereidentified.Ofthetwominerswhocaredfortheindexcasewhodied,onealsosufferedafatalillness(WHO2007).

InJuly2008,aDutchtouristdevelopedMarburgfourdaysafterreturningtotheNetherlandsfromathree-weekholidayinUganda.Thesourceoftheexposurehasnotbeendetermined,althoughthewomanhadvisitedcavesinMaramagambo


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ForestwesternUgandaatthesouthernedgeofQueenElizabethNationalpark,wherebatswerepresent(WHO2008;Timen2009).

Therehavebeen414primaryhumanMarburginfectionsdocumentedandanincreasingnumberofsecondarycasesrecordedwhichhaveoriginatedfromanincreasinggeographicrangeinAfrica(Table31.2).

Table31.2Summaryofhumanfilovirusinfectionsduringidentifiedoutbreaks

Year Filovirus Sourceofinfection Allcasesdeaths/total

Overallmortalityrate(%)

Source Comments

1967 Marburgvirus Germany,Marburg 5/23 22.6 Vervetmonkeys

ImportedfromUganda

Germany,Frankfurt 2/6

Yugoslavia,Belgrade 0/2

1975 Marburgvirus Zimbabwe/SouthAfrica(Johannesburg)

1/3 33.3 Unknown IndexcaseinfectedinZimbabwe.Secondarycases:–travellingcompanionandnurse

1976 Zaireebolavirus

NorthernZaire(Yambuka)

280/318 88.1 Unknown Indexcaseintroducedvirusintohospital

1976 Sudanebolavirus

Sudan,Maridi 116/213 53.2 Unknown Diseaseamplifiedbytransmissioninlargeactivehospital

Sudan,Nazara 31/67

Sudan,Tembura 3/3

Sudan,Juba 1/1 OriginatedinNazaracottonfactory


UnitedKingdom,PortonDown

0/1 0 Laboratoryinfection

Needle-stick

1977 (Zaireebolavirus)

Zaire,Tandala 1/1 100 Unknown Tandala


SouthernSudan,Yambo-NazarDistrict,

22/34 64.7 Unknown Nazara,Maridi&localarea

1980 Marburgvirus Kenya,MountElgon 1/2 50 Unknown VisitedKitum


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1980 Marburgvirus Kenya,MountElgon 1/2 50 Unknown VisitedKitumcaveinnationalpark

1987 Marburgvirus Kenya,MountElgon,Kisumu

1/1 100 Unknown ExpatriatetravellinginwesternKenya.VisitedKitumcave

1988 Marburgvirus USSR(Koltsova) 1/1 100 Laboratoryinfection

Associatedwithanimalstudies

1989-1990

Restonebolavirus

US(Alice,Philadelphia,Reston)

0/4 0 Monkeys Epizootic-importedmonkeysfromexportfacilityinPhilippines

1990 Restonebolavirus

Philippines(Luzon) 0/12 0 Monkeys Exportfacility

1990 Marburgvirus USSR(Koltsovo) 0/1 0 Laboratoryinfection



Italy,Sienna 0 0 Monkeys Epizootic-importfromexportfacilityinPhilippinessameasUSoutbreakin1989

1994 Côted’Ivoireebolavirus

Côted’Ivoire,Taiforest

0/1 0 Chimpanzees ContractedinScientistduringpost-mortemofchimpanzee—repatriatedtoSwitzerland

1994-1995

Zaireebolavirus

Gabon(Andok,Mekouka,Minkebe,Mayela-Mbeza,Ovan,Etakangaye)

31/52 60 Unknown


Zaire,Kikwit 245/317 77.3 Unknown ConfinedtoBandundoregionaroundKikwit

1996 Zaireebolavirus-

Gabon(Mayibout,Makokou)

21/37 57 Chimpanzees Contactwithdeadprimateshuntedfor


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huntedforfood


Russia(SergiyevPosad-6)

1/1 100 Laboratoryinfection


1996-1997

Zaireebolavirus

Gabon(Balimba,Boouee,Lastourville,Libreville,Lolo),SouthAfrica(Johannesburg)

46/62 74.2 Chimpanzee? IndexcasehunterNursetreatingimportedcasefromGabontoJohannesburg


USA 0 0 Monkeys Epizootic-PrimatesimportedfromPhillipinestoquarantinefacilityinTexas


Phillipines 0 0 Monkeys Epizootic-IdentifiedinExportfacility.Nohumaninfections

1998-2000

Marburgvirus DemocraticRepublicofCongo(Durba,Watsa)

128/154 83.1 Unknown EpicentreofoutbreakinyoungmalegoldworkersinDurba

2000-2001

Sudanebolavirus

Uganda(Gulu,Masindi&MbararaDisricts)

224/425 52.7 Unknown Spreadthroughattendingfunerals,familycasecontact&medicalcentres

2001-2002

Zaireebolavirus

Gabon(Ekata,Etakangaye,Franceville,GrandEtoumbi,Ilahounene,

53/65 82 Unknown CommunityandNosocomialspreadonborderregionofGabonandCongo

2001-2002

Zaireebolavirus

Congo(Abolo,Ambomi,Entsiami,Kelle,Olloba

43/57 75.6 Unknown


Congo(Olloba/Gabon(Etata))

10/11 90.9 Unknown

2002- Zaire RepublicofCongo 129/143 89 Unknown


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2002-2003

Zaireebolavirus

RepublicofCongo(Mbomo&Kelledistrictsof)

129/143 89 Unknown

2003-2004

Zaireebolavirus

RepublicofCongo(MbomoandMbandzavillagesinMbomodistrictof)

29/35 83 Unknown


Russia(Koltsovo) 1/1 100 Laboratoryinfection

GuineapigadaptedZaireebolavirus

2004-2005

Marburgvirus Angola,UigeProvince

227/252 90.1 Unknown CommunityspreadthroughvariousprovinceslinkedtoUige


Sudan(Yambio) 7/17 41-.2 Unknown Simultaneousoutbreakofmeasles


Congo(Etoumbi,Mbomo)

9/11 81.9 Unknown

2007 Marburgvirus Uganda(KamwengeDistrict)

2/3 66.6 Unknown OriginsthoughttobeinLeadandGoldminesofarea


DemocraticRepublicofCongoKasaiOccidentalprovince

187/264 70.8 Unknown

2007-2008

Bundibugyoebolavirus

Uganda(BundibugyoDistrict)

25/149 16.8 Unknown 1strecordedoccurrenceofnewstrain

2008 Marburgvirus NetherlandsexUganda(MaramagamboForest)

1/1 100 CaveinMaramagambobats?

40yearoldDutchwomen,visitedcaveinNationalPark

2008 Ebola-Reston

Phillipines 6assymptomticcases

0 Pigs 1stknowndetectionofEbola-Restoninpigs.6assymptomticcasesamongstslaughterhouseworkers.


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2008-2009

Zaireebolavirus

DemocraticRepublicofCongo

15/32 47 OutbreakinMweka&LueboofKasaiDistrict


Germany 0/1 0 Laboratoryinfection

Animalvaccinestudies

In1976,asevereandoftenfatalviralhaemorrhagicfeveroccurredinsimultaneousoutbreaksintheequatorialprovincesofsouthernSudanandnorthernZaire(Table31.2).Amongsttheseveralhundredcasesofinfectionidentified,fatalityratesofabout90and60%respectivelyoccurred.Severalgenerationsofhuman-to-humanspreadcontributedtotheseverityoftheoutbreak.ThetwovirusstrainsisolatedfrompatientsinSudanandZairewherefoundtobemorphologicallyidenticaltoMarburgbutantigenicallyandbiologicallydistinct(Bowenetal.1977;WHO1978a,b).TheviruswasnamedEbolaafterariverinZaire.

Numerousfollow-upecologicalstudieshavefailedtodiscoverthereservoir.DuringstudiesoftheSudaneseepidemicin1976,anon-fatalEbolainfectionoccurredwithintheUKin1977afteralaboratoryaccident(Emondetal.1977).Justover6monthsaftertheoriginaloutbreaksinZaire,a9yearoldgirldiedofacutehaemorrhagicfeverinTandala,northernZaire(Heymannetal.1980).AfurthersmallepidemicoccurredinthesameregionofSudanin1979when22(65%)of34infectionswerefatal,withtransmissibilitybeingassociatedwithperson-to-personspread(Baronetal.1983).ThegeographicareawidenedwhenaSwisszoologistbecameinfectedwhileundertakinganautopsyofadeadchimpanzeeinwesternCôted’Ivoireinlate1994.Thisresultedinhercontractinganon-fatalsevereEbolaillness(LeGuennoetal.1995).OnlyafterhertreatmentanddischargefromahospitalinSwitzerlandwasitdiscoveredthatshehadsufferedfromanEbolainfection.Alarger-scaleoutbreakinKikwit,BandunduProvince,Zaire1995demonstratedtoaworldwideaudienceaseverehemorrhagicillnessinvolvingsome316cases,ofwhich244died,givingamortalityrateof77%(WHO1995a).Athirdofthecasesinvolvedhealthcareworkers.TheKikwitoutbreakwassimilartotheoriginalepisodethatoccurredin1976,1000kmtothenorth.Asinpreviousoutbreaks,secondarycasesoccurredthroughclosepersonnelcontactwithinfectiousbodyfluids.Theuncontrolledspreadofinfectionresultedfromalackofmodernmedicalfacilitiesandsuppliesthatcouldprotectmedicalpersonnelfromthosepatientsinitiallyaffected.UnlikepreviousEbolaoutbreaks,concerncenteredonthepotentialforcommunity-widespreadfromKikwit,alargeanddenselypopulatedarea,tothelargercitesofKinshasaandBrazzavillecloseby.Controloftheoutbreakcoincidedwiththeintroductionofprotectiveequipmentandbarriernursingtechniques(WHO1995b).TherecognitionofEbolahasrecentlyextendedtoaconfirmedcaseintheCôted’IvoireofarefugeefromneighbouringLiberiainlate1995;othercaseswerereportedtoexistinhishomevillageinLiberia(WHO1995c).

During1996–1997,twosmalloutbreaksoccurredinGabon.ThesewerefoundintheforestregionsofMayiboutandBoouéareasandwhereassociatedwithpeoplehuntingandbutcheryofchimpanzees(Georges1999).Amajoroutbreakinvolving425casesoccurringforthefirsttimeinUgandaduring2000–2001.StudiesindicatedthatthethreemostimportriskfactorsassociatedwithitsspreadwereassociatedwithattendanceatfuneralsofEbolafevercases,havingdirectcontactwithcasesandprovisionofmedicalcarewithoutadequatepersonalprotectivemeasuresbeingused.Thegeographicalspreadcontinuedduring2001–3whenEbolaoutbreakswithcasemortalityratesreachingover80%wasrecordedinGabonandforthefirsttimeinTheDemocraticRepublicofCongo(DRC)(Okware2002;WHO2003;Formenty2003;WHO2004).RepeatoutbreaksintheDRCin2007andinUgandain2007–08producedcasefatalityratesof70%and25%respectively.

Unexpectedly,EbolavirushasalsoappearedoutsideAfricawhenidentifiedamongstcynomologusmonkeys(Macacafasicularis)importedintotheUSAin1989(Jahrlingetal.1990)andSiena,Italyin1992(WHO1992).Shipmentsofwild-caughtcynomolgusmonkeysoriginatedfromthesamehandlingfacilityinthePhilippines,wherethepresenceoftheviruswasdocumented.AlthoughatrulyAsianoriginforthesevirusstrainsisnotdiscounted,preliminaryserologicalandsequencingstudies,suggestaclosesimilaritywithisolatesfromthe1976Africanoutbreaks.

Theagent

Taxonomy

EbolaandMarburgaremembersofthefamilyFiloviridae(Kileyetal.1982;Pringle1991),namedfortheirfilamentousappearanceundertheelectronmicroscope(Fig.31.1a).SimilaritiesofgenomestructureandcomparablemechanismsofgeneexpressionsuggestthatthefiloviruseshaveanevolutionaryoriginincommonwiththefamiliesParamyxoviridae(whichincludemeaslesandmumps)andRhabdoviridae(whichincludesrabies)(Sanchezetal.1992).Thesethreevirusfamiliesaregroupedintoataxonomicorder(Table31.1),theMononegavirales(BishopandPringle1995).


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ProgressivecharacterizationofthefilovirusesrevealedsubstantialdifferencesbetweentheMarburgvirusesandEbolaviruses(Richman1983)leadingtotheestablishmentoftwogenera,MarburgvirusandEbolavirus,withinthefamilyFiloviridae(Feldmann1994).ThegenusMarburgviruscontainsonlyonespecies,LakeVictoriaMarburgvirus,representedbyasinglevirus,LakeVictoriaMarburgvirus(MARV).ThegenusEbolaviruscurrentlycontainsfivespecies:Côted’Ivoireebolavirus(Côted’Ivoireebolavirus,CIEBOV),Restonebolavirus(Restonebolavirus,REBOV),Sudanebolavirus(Sudanebolavirus,SEBOV),‘Ugandaebolavirus’(‘Ugandaebolavirus,’‘UEBOV’),andZaireebolavirus(Zaireebolavirus,ZEBOV)(Feldmann2005;Mason2008)(Table31.3).Incomparison,thegenomesofmembersofthefiveebolaviralspeciesdiffergeneticallyby37–41%atthenucleotidelevel,andallofthemdifferfromMARVgenomesby>65%.AmongstthegenusEbolavirusthethreedistinctspecies,Bundibugyo,SudanandZairespecieshavebeenassociatedwithlargeoutbreaksofEbolahaemorrhagicfever(EHF)inAfricacausingdeathin25–90%ofallclinicalcases,whileCôted’IvoireandRestonhavenot.

Table31.3Filovirustaxonomy

Order Family Genus Species Abbreviation

Mononegavirales Filoviridae EbolavirusMarburgvirus

SudanebolavirusZaireebolavirusCoted’IvoireebolavirusRestonebolavirusBundibugyoebolavirusLakeVictoriamarburgvirus

SEBOVZEBOVCIEBOVREBOVBUBOVMARV

Molecularbiology

Filoviralgenomesconsistsofasinglenon-segmentednegative-strandedRNAabout19kilobasesinlengthandcontainsevengenesarrangedlinearlyandthatmaybeseparatedbyintergenicregions.Thelineararrangementofgenesfollowsasequencebeginningwitha3′non-codinguntranslatedregion,thecoreproteingenes,envelopegenes,andthepolymerasegeneattachedtotheuntranslatedregionatthe5′end.(Feldmannetal.1993;Sanchezetal.1993).Non-structuralproteinsarenotpresent.EachgeneisflankedbyhighlyconservedtranscriptionandterminationsitesthatdifferamongthedifferentFiloviruses(Weik2002).

ThegeneticsequenceofMarburgvirus(MBG)andtheavailablepartialsequenceofEbolavirus(EBO)indicatethatinbothcasessevenstructuralproteinsareencoded,whichareexpressedthroughtranscriptionofmonocistronicmRNAspecies.Thefirst(3’)geneofthefiloviralgenomes,NPamajornucleoprotein(NP;M 94–104).ThenucleocapsidiscomposedofRNA,L,NP,VP35,andVP30.AnalysisoftheNPgeneshowsashortputativeleadersequenceattheextreme3endfollowedbythecompletenucleoproteingene.Thetranscriptionalstart(3′…UUCUUCUUAUAAUU…)andtermination(3′…UAAUUCUUUUU)signalsoftheMBGNPgeneareverysimilartothoseseenwithEBOvirus.ThefiloviralVP35geneislocatedimmediatelydownstreamoftheNPgene.TheVP35proteinisthoughttobeatranscriptase–polymerasecomponentthatisconsideredtobetheP(NS)proteinequivalentofparamyxo-andrhabdovirusesTheVP35andVP35-NPcomplexesalsoinhibitbothdsRNA-mediatedandvirus-mediatedinductionofinterferon-responsivepromotersandconsequentlythecellularinterferoninnateimmuneresponsetovirusinfection.Thefiloviralmatrixormembrane-associatedVP40geneislocateddownstreamoftheVP35geneandisthemostconservedofallfilovirusgenes,itencodesthematrixproteinVP40protein(M 32000).ThefiloviralGPgeneisasinglesurfaceglycoprotein(GP;M 170000).MarburgandebolavirusencodeoneandthreeglycoproteinsfromtheirGPgenes,respectivelyThefiloviralminornucleoproteinVP30gene(VP30;M 32000),locateddownstreamoftheGPgene,isanotheruniquecomponentofthefiloviralgenomes.Itencodesaprotein,VP30.TheN-terminusofVP30bindsdirectlytosingle-strandedRNA,andprefersfiloviralRNAoverunspecificRNA(John2007)VP30isalsoazinc-bindingprotein.Intheabsenceofzinc,filovirus-genometranscriptionisabolished(Modrof2003)).TheVP24geneanditsexpressionproductisasecondmatrixormembrane-associatedVP24protein(M 24000).RecentexperimentsalsoindicatethatVP24counteractstheinterferon-responseofvirus-infectedcells(Reid2007).Thelast(5’)geneofthefiloviralgenomeistheLgene,whichencodesthecatalyticpart(Lprotein;MARV:2,331amino-acidresidues,267kD;ZEBOV:2,212amino-acidresidues,253kD)oftheviralRNA-dependentRNApolymeraseholoenzyme,(M 267000);whichalsocontainsVP35(27,195,283).

Incomparisontoothernon-structuralnon-segmentednegative-strand(NNS)RNAviruses,filovirustranscriptionalsignalsareverysimilartothoseofmembersoftheparamyxovirusandmorbillivirusgenera.Nucleotidesequenceanalysisofthe3’end,includingtheentireNPandLproteinencodinggenesoftheMBGandEBOgenome,hasshownsimilarstructureandorganizationwithotherNNSRNAviruses.ThesimilarityofthefilovirusNPgenesandgeneproductstothoseoftheparamyxovirusesimplyacloserbiologicalandphylogeneticrelationshiptotheseagentsthantorhabdoviruses.

r

r r

r

r

r


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Growthandsurvival

Filovirusesundergorapid,lyticreplicationinthecytoplasmofawiderangeofhostcells.ThemodeofentryofFilovirusesintocellsoccursbybindingtounidentifiedcell-surfacereceptorswiththeirspikeproteins.Althoughsomeultrastructuralstudieshavesuggestedthatvirionsareassociatedwithentrybyendocytosis.Africangreenmonkeykidneycells,suchasCV-1andVeroderivatives,arecommonlyusedtogrowfilovirusestohightitres.Thefiloviralnucleocapsidisreleasedintothecytosolsubsequenttofusionoftheviralandcellularmembrane,andcompleteuncoatingofthefilovirusgenometakesplace.ThepolymeraseholoenzymeL/VP35,broughtintothecellwiththenucleocapsid,transcribesthefilovirusgenesinasequence,synethizingtheantigenomethatisusedasthetemplatetosynthesizetheprogenygenes.ThefiloviralmessengerRNA’sareabundantininfectedcellsandaretranslatedintothefiloviralstructuralproteins.TheNP,VP30,VP35andLproteinsassemblewiththenewlysynthesizedgenomestoformRNPscomplexes.TheserecruitthematrixproteinsVP40andVP24andbudfromthecell’splasmamembrane,acquiringtheGPenvelopewithitssurfaceprojectionsbybuddingfromthecellmembranes(Noda2006).Theentirelifecycleoccursinthecytoplasmofthehostcell.Nucleocapsidsalsoaccumulateinthecytoplasm,formingprominentinclusionbodies.

Laboratoryinfectionoftissuecellsshowsintracytoplasmicvesiculationandmitochondrialswellingfollowedbyabreakdownoforganellesandterminalrarificationandcondensation.Thesecytoplasmicchangesoccursimultaneouslywiththeaccumulationofviralnucleocapsidmaterialinintracytoplasmicinclusionbodiesandthelargenumbersofvirionsextracellularly(Fig.31.1b).

Thefilovirusvirionisbacilliforminstructureandiscomposedofahelicalnucleocapsid,consistingofacentralaxis(20–30nmindiameter),surroundedbyahelicalcapsid(40–50nmindiameter).Ahostcellmembranederivedlipidouterenvelope,withregular10nmprojectionssurroundsthenucleocapsidandcompletesthestrikingandcharacteristicappearanceundertheelectronmicroscope(Fig.31.1a).Althoughthereareoftenstructuresofvaryinglength,withloops,branches,andotherirregularities,evidenceexiststhatinfectiousparticlesconsistmainlyofsimplelinearformsabout1μminlength.

MarburgandEbolavirusinfectivityarestabilizedatambienttemperature(18–20°C)butinactivatedwithin30minat60°C.Ultravioletandgammairradiation,lipids,solvents,β-propiolactone,hypochlorite,andphenolicdisinfectantsalldestroyinfectivity.

Diseasemechanisms

Theexactmechanismbywhichfilovirusescausesuchaseriousillnessisbeingunravelled.Thereisextensiveviralreplicationinliver,lymphoidorgans,andkidneys.Extensivevisceraleffusions,pulmonaryinterstitialoedema,andrenaltubulardysfunctionoccurringafterendothelialdamageleadingtohypovolaemicshockareallobservationscontributingtodeath.Severe,acutefluidlossaccompaniedbybleedingintothetissueandgastrointestinaltractischaracteristicandleadstodehydration,electrolyteandacid-baseimbalance.Inprimatesandclinicalcasesstudiedearly,lymphopeniaisfollowedbyamarkedneutropenia(Fisher-Hochetal.1983).Inthelaterstagesoftheinfection,andinassociationwiththethrombocytopenia,theremainingplateletsareunabletoaggregateinresponsetoADPorcollagen.Ithasbeensuggestedthatthedysfunctionofplateletsandendotheliaextendstootherelementsoftheendothelialsystem,suchasmacrophages(Fisher-Hochetal.1985).InexperimentalmonkeyEbolainfections,virushasbeenidentifiedinvascularendothelialcells.HumansconvalescentfromMarburgandEbolainfectionshavehadvirusisolatedupto3–4monthsafteronsetinsemen,inapatientwithuveitis,anteriorchamberfluid.Thereisnoevidenceoflong-termpersistence,latencyorlatedegenerativediseaseinthesmallnumberofpatientsobservedorinmonkeysrecoveringfromthedisease(Fisher-Hochetal.1992a).

Thehosts

Human

Incubationperiod

Filovirusesaretransmittedthroughdirectcontact.Theyenterthroughsmallskinlesionsorthroughdamagedmucousmembranesandinitiallyinfecttargetcellssuchasmacrophages,whichtransportthemthroughthebody.TheincubationperiodforMarburgvirusdiseaseis3–9days(Martini1971;Bausch,2006)andforEbolavirusabout10days(Bwaka1999)5–7daysforneedletransmission(Emond1978)and6–12daysforperson-to-personspread.

Symptomsandsigns

TheillnessescausedbyMarburgandEbolavirusesarevirtuallyindistinguishable.Followingexposureandincubationperiod,bothinfectionshaveanabruptonsetofillnesswithinitialnon-specificsymptomssuchasfever,severefrontalheadache,backpainmalaise,andmyalgia.Earlysignsincludetachycardia,conjunctivitis,andmaculopapularrashes,


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whichdevelopafter5–7daysonface,buttocks,trunkorarmsandlatergeneralizesovertheentirebodywithdesquamationinsurvivors.Withinaweekto10days,thosedestinedforrecoverybegintoimprove,eventhoughrecoveryfromtheseveredebilitatingeffectsofthediseaseoftentakesweeks.AlargenumberofpatientsinbothMarburgandEbolaoutbreaksdevelopseverebleedingbetweenthefifthandseventhdays.Patientswithsevereinfectionsoftenexperiencepharyngitis,severenausea,andvomiting,progressingtohaematemesisandmelena.Petechiae,ecchymoses,uncontrolledbleedingfromvenepuncturesitesandpost-mortemevidenceofvisceralhaemorrhagiceffusionsarecharacteristicofsevereillness(Smithetal.1978).Deathusuallyoccursbetweenthe7–10days(range1–21days)afteronsetofclinicaldiseaseandisprecededbyseverebloodlossandshock.Convalescenceisslowandmarkedbyprostration,weightloss,andamnesiaforaconsiderableperiodaftertheacuteillness(Piot1978;Formenty1999).Deathoccursusuallyafter8–16daysofinfectionduetoshockaftermulti-organfailure,oftenbroughtonbysecondarybacterialinfections.

Clinicallaboratoryfindingsincludeearlyleucopoeniawithleftshiftofthegranulocytesaccompaniedby,markedthrombocytopenia,andabnormalplateletaggregation.Serumaspartateaminotransferase(AST)/alanineaminotransferase(ALT)enzymelevelsareraisedandcharacterizedbyahighAST/ALTratio(10–3:1)andγ-glutamyltranspeptidaseindicatingliverdamage.Otherfindingsincluderaisedlevelsofcreatineandurealevelspriortorenalfailureandhypokalemiabecauseofthediarrheaandvomiting.

Asthedifferentialdiagnosisintheearlyacutephaseisdifficult,othercausesneedconsideration.Themostcommoncausesofimportedinfectionsshowingasevere,acutefebrilediseasearemalariaandtyphoidfever.Therefore,delayindifferentialdiagnosisandtreatmentneedstobeminimized.Alternativecausesincludebacterialdiseasessuchasmeningococcalsepticaemia,Yersiniapestisinfection,leptospirosis,anthrax;rickettisaldiseasessuchastyphusandmurinetyphus;andviraldiseasessuchassandflyfever,yellowfever,chikungunyafever,RiftValleyfever,hantavirus,andCongoCrimeanhaemorrhagicfever.

Diagnosis

ThediagnosisofEbolaorMarburgshouldbeconsideredinpatientsshowingacute,febrileillnesshavingvisitedknownepidemicorsuspectedendemicareasofruralsub-SaharanAfricaandAsia,particularlywhenhaemorrhagicsignsarepresent.Alltissues,blood,andserumcollectedintheacutestagesofillnesscontainlargeamountsofinfectiousvirus.Extremecareshouldbetakenwhendrawingorhandlingbloodspecimensasthevirusisstableforlongperiodsatroomtemperature(Elliottetal.1982).Allneedlesandsyringesneeddiscardingtopuncture-resistantcontainerswithlids,andincinerated.Specimensofbloodshouldbetakenwithoutanticoagulant.Bloodorserumshouldbetransferredtoaleakproofplasticcontaineranddoublewrappedinleakproofcontainersfortransportationtoahighcontainmentlaboratory.Transportationshouldbeunderappropriatebiocontainmentwithindryorweticeaccordingtointernationaltransportationornationalregulations(DepartmentofHealth2007;WHO2007)afterconsultationwithanyoftheglobalmaximumcontainmentreferencelaboratories.

Inactivationofpatientsserawithirradiationorheatingat60°Cfor30minrenderthemsafeforundertakingimmunoassaytests.Althoughmorphologicallysimilar,MarburgandEbolaareimmunologicallydistinct.Theimmunofluorescenceassay(IFA)hasbeenthebasicdiagnostictestforfilovirusinfectionandtheonlyonethathaswidespreadacceptanceforthediagnosisofhumanEboladisease(WulffandJohnson1979;Rollinetal.1990).ArisingantibodyinpairedserumorahighIgGtitre(>64)andpresenceofIgMantibody,togetherwithclinicalsymptomscompatiblewithahaemorrhagicfever,areconsistentwithadiagnosis.ThepresenceofMarburgantibodyisconsideredaspecificresultbutEbolaviruslow-titre,non-specific,false-positiveserologicalreactionsdooccur.WhenusingIFAtheproblemoflow-titrefalsepositivesmakesinterpretationdifficultwhenundertakingnon-humanprimateandhumanseroepidemiologicalsurveys.FortheIFA,theantigensubstrateconsistsofvirus-infectedVerocellsdriedontospotslides.RecentadvancesinmolecularbiologyhaveexpressedthenucleoproteingeneofEbolavirusinabaculovirusexpressionsystem.Thus,alargeamountofnon-infectiousproteinisapossiblesourceofantigenformanyserologicaltests(IFA,ELISA).Thereevaluationleadingtoanimprovementinthedetectioncapabilitywithinseroepidemiologicalfieldstudiesandinthescreeningofimportedprimates.

Filovirusescanbeeasilyisolatedfrominoculationoffreshorstored(−70°C)specimensofbloodorserumcollectedduringtheacutephaseofillnessintoVeromonkeykidneytissueculturescellsusinglaboratorycontainmentlevel4facilities.Verocells(particularlycloneE6)andMA-104haveprovedtobethemostsensitiveandusefulcellsforthepropagationandassayoffreshisolatesandlaboratorypassagefilovirusstrains.Primaryisolationusingtissueculturerarelyproducesaspecificcytoplasmiceffect,thusevidenceofinfectionisbasedontheappearanceofcytoplasmicinclusionbodiesdemonstrated2–5daysafterinoculation,byimmunofluoresencestaining,usingantipolyclonalanti-seraorvirussubtypeorstrain-specificmonoclonalantibodies.SomefilovirusstrainssuchasEbolaSudanaredifficulttogrowinprimaryculturesandsuccessisimprovedthroughtheintraperitonealinoculationofyoungguineapigs.Amonitoredfebrileresponsecoincideswithhighlevelsofvirusintheblood,whichcanberecoveredintissuecultureorexamineddirectlybytheelectronmicroscope.IneachoftheFiloviridaeoutbreakselectronmicroscopyhasprovenusefulintheidentificationofMarburgorEbolainbodyfluidsandtissue,andcellculturesupernatants.DuringtheRestonepizootic,


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immunoelectronmicroscopy,whenusedinconjunctionwithstandardtransmissionmicroscopy(TEM)ofinfectedcells,providedconsistentresults(GeisbertandJahrling1990).However,thetechniquewillnotdistinguishbetweentheFiloviridaestrains.Virusmayalsobedetectedinarangeofspecimens,includingthroatwashings,semenandanterioreyefluid.Thepresence,ofEbolaandMarburgintissuesofmonkeys,bothexperimentallyandduringprimateoutbreaks,hasbeendemonstratedbyelectronmicroscopy(Baskervilleetal.1985;GeisbertandJahrling1990);anddetectionofhightitresinthebloodofinfectedpatientsandmonkeysindicatedtheusefulnessofanantigencaptureELISAsystem(Ksiazeketal.1992).SuchasystemhasbeenofconsiderableuseintherecentKikwitepidemic.ImmunobilizedmousemonoclonalantibodiesonasolidplasticsurfacecaptureEbolaantigencontainedintissueorbloodspecimens.Rabbitpolyclonalanti-filovirusserumdetectstheantigen.Theantigenimmunoabsorbentdetectionassayhasprovedarapidandreliableprocedurefortheearlydetectionoffilovirusinfectionsandwouldproveusefulasamethodfortheroutinescreeningofimportedprimates.

Inrecentyears,theuseofcross-reactingandstrain-specificprobesforthereversetranscriptasepolymerasechainreactionRT-PCRhasevolvedtothegoldstandardforFilovirusdiagnosisinthefieldandhastakentheplaceofpreviouslywidelyusedIFAsandELISAs.ConfirmatorydiagnosisofRT-PCR-positivesamplesisusuallyperformedbyvirusisolationinmaximum-containmentfacilities(Grollaetal.2005;Towneretal.2004).

CurrentlyalloutbreaksofEHFandMHF,infectionsareconfirmedbyvariouslaboratorydiagnosticmethods.Theseincludevirusisolation,reversetranscription-PCR(RT-PCR),includingreal-timequantitativeRT-PCR,antigen-captureenzyme-linkedimmunosorbentassay(ELISA),antigendetectionbyimmunostaining,andIgG-andIgM-ELISAusingauthenticvirusantigens(Gibbetal.2001;Ksiazeketal.1992,1999;Leroyetal.2000;Towneretal.2004;Zakietal.1999;Saijoetal.2006).

Primates

AfricangreenmonkeysimportedfromUgandaweretheidentifiedsourceoftheMarburgoutbreak(Hendersonetal.1971),andcynomolgusmonkeysthesourceebolarestonvirus.Bothspecieswereimportedandcloselyassociatedwithmedicalresearch.

Thegeneralcharacteristicsofprimatefilovirusinfectionsamongstexperimentallyandnaturallyinfectedprimatessuggestthattheincubationperiodvariesbetween4and20days,duringwhichtimethevirusreplicatestohightitreintheliver,spleen,lymphnodes,andlungs.Theclinicopathologicalfeaturesnotedincludehighfever,severeweightloss,anorexia,haemorrhages,andadistinctiveskinrashinassociationwithsplenomegaly,markedelevationoflactatedehydrogenase,alanineaminotransferaseandaspartateaminotransferase.TheASTlevelsareconstantly2–10timeshigherthanthatofALT.Evidenceofthrombocytopeniaisapronouncedfeaturebutanaemiaisnot.Bothlymphocytopeniaandleucocytosisareevidentanddependentonthestageoftheinfection(Fisher-Hochetal.1983).Severeprostrationwithdiarrhoeaandbleedingleadstorapiddeathinalmostallanimals.Theseverityofthediseaseinprimatesdependsonthefilovirusinfectionandhostinvolved.AfricangreenmonkeysarefarlesssusceptibletosevereorfataldiseaseduetoEbolavirus(Sudan)orEbola(Reston)thancynomolgusmonkeys.However,AfricangreenmonkeysexperimentallyinfectedwithMarburgvirusafterthe1967outbreakalldiedirrespectiveofrouteofinfection(HassandMass1971).Marburgvirusinfectionofrhesusmonkeysislesssevereorfatal,similartoEbola(Sudan)infection.InfectionbyEbolavirus(Zaire)isuniformlyfatalinallspeciessofarchallenged,regardlessofinoculum.

Histopathologicalfindingsincludeseverehepatocellularnecrosis,necrosisofthezonaglomerulosaoftheadrenalcortex,andinterstitialpneumonia,allassociatedwiththepresenceofintracytoplasmicamphophilicinclusionbodies.Thenecroticlesionsresultfromdirectvirusinfectionoftheparenchymalcells.Littleinflammatoryresponseoccursatthesiteofthelesions.

Experimentalpathophysiologicalstudieshavedemonstratedendothelialcellandplateletdysfunctionaccompaniedbyoedema,multipleeffusions,haemorrhage,andhypovolaemicshock(Fisher-Hochetal.1985).RecentstudiesinMacacafascicularisandCercopithecusaethiopssuggestthattherecentlyisolatedAsianfilovirusesarelesspathogenicforprimatesthantheAfricanfiloviruses(Fisher-Hochetal.1992b).

Treatmentandprognosis

Thereisnolicensedvaccineoreffectiveantiviraldrugtreatmentlicensedforuseinhuman.TherapyforMarburgandEbolavirusinfectionislimitedtotheprovisionofsupportivemeasuresandgeneralnursingcare.Inthedevelopmentofvaccines,recentadvanceshaveshownprotectioninanimalmodels.Amongstthemostrecentpromisingvaccinesunderdevelopmentareanumberofrecombinantbasedsystems.Themostnoticeablethosebasedvesicularstomatitisvirus(VSV)thatexpressesasinglefilovirusglycoprotein(GP)inplaceoftheVSVglycoprotein.Asingledosevaccinehasprovedcapableofprotectingnon-humanprimatesagainstSudanebolavirus(SEBOV),Zaireebolavirus(ZEBOV),Coted’Ivoireebolavirus(CIEBOV),andMarburgvirus(MARV)(FeldmannHetal.2007;Geisbertetal.2009).Recently,atwo-


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injectionfilovirusvaccineregimebasedonanadenovirusvectorexpressingmultipleantigensfromfivedifferentfiloviruses,(ZEBOVNP,ZEBOVGP,SEBOVGP,MARVCi67strainGP,MARVRavnstrainGP,MARVMusokestrainNP,MARVMusokestrainGP),provedsuccessful(Prattetal.2010).Allanimalsinthesestudiessurvivedtheinitialfiloviruschallengewithadifferentstrainorspeciesoffilovirus.However,thereareanumberofsignificantsafetychallengesinhumans;particularlythosewithanalteredimmunestatusareyettobeovercome.

Intensivesupportivecareiscurrentlyconsideredmostimportant:preventionofshock,cerebraloedema,renalfailure,bacterialsuperinfection,hypoxia,andhypotensionmaybelifesaving.Patientcareiscomplicatedbytheneedforisolationandprotectionofmedicalandnursingpersonnel.Theuseofplasticpatientisolatorsisarequirementinmanycountries,includingtheUKandEurope,despitethereturntothestrictbarriernursingtechniquesnowfavouredintheUSAandintherecentAfricanoutbreaksinZaire,Côted’Ivoire,Gabon,UgandaandAngola.

Epidemiology

Epidemics

Marburgvirusdisease

AfulminatinghaemorrhagicfevercausedbytheMarburgviruswasfirstrecognizedinAugust1967whenitaffectedlaboratoryworkersinthreesimultaneousoutbreaksinMarburgandFrankfurt,Germany,andBelgrade,formerYugoslavia(Martini1969).Altogether,therewere31humaninfections,ofwhom25hadprimaryinfectionsacquiredthroughcontactofbloodandtissuesfromshipmentsofAfricangreenmonkeys(Cercopithecusaethiops)importedfromUganda,viaLondon.Thelargestnumberofprimaryinfections(20)occurredamongworkersofaMarburgpharmaceuticalfirmwhopreparedkidneycellsforvaccineproduction.Amongthoseinfected,exposurewasattributedtoautopsies(13),cleaningofcontaminatedglassware(5),dissectionofkidneys(1),andlaboratoryaccidentinvolvingcontaminatedbrokenglassware(1).Personnelnotindirectcontactwithcontaminatedmaterialorwhoworeprotectiveglovesormasksforworkwithmonkeyswasnotinfected.InFrankfurt,fourfurtherprimaryinfectionsoccurredinworkersexposedtotissueculture.Aveterinaryofficercarryingoutroutinepost-mortemswasthesinglerecordedprimarycaseinBelgrade.Fourofthesecondaryinfectionsoccurredinhospitalpersonnelwhocameintoclosecontactwithpatients.Thefifthwasthewifeoftheveterinarysurgeon,whofellill10daysafternursingherhusbandathome.Thesixthcaseinvolvedthewifeofapatientwhohadtransmittedthediseasethroughsexualintercourse83daysaftertheillness.Sevenoftheprimarycaseswerefatal,butnofatalitiesoccurredamongstthesixsecondarycases.

Around600animalsoriginatingfromfourshipmentsreachedEuropefromUgandaovera3-weekperiod.Frankfurtreceived50–60animalsfromtwoshipments,Belgradeapproximately300animalsfromthreeshipments,andtheremainderwenttoMarburg.Allspentbetween60and87daysinaholdingfacilityinUgandabeforebeingshippedtoLondon,Heathrowwheretheyspent636hoursintheanimalhostelbeforebeingforwardedtoGermany.DetailsontheBelgradeenzooticindicatedthat46of99animalsimportedfromthefirstshipmentdied,and20and30fromthesecondandthirdshipments,respectively.Thisepizooticwascharacterizedbydailydeathsofoneormoreanimalsthroughoutthe6-weekquarantineperiod,suggestingongoingtransmissionbetweenanimals.Epidemiologicalevidenceoftheoutbreaksuggestedthattransmissionbetweenmonkeysinquarantinefacilitieswasthroughdirectcontactwithcontaminatedequipment.Directcontactwithinfectedbloodandtissuewasconsideredthesourceforallhumancases,andtherewasevidenceofaerosoltransmission.NoepizooticswerefoundinUgandaalthoughuncorroboratedinformationhadsuggestedalargenumberofmonkeydeathsincoloniesontheislandnearLakeKyoga,northofLakeVictoria,totheeastofMountElgoninKenya.Ugandanmonkeyswerecapturedinthisarea,transportedtoEntebbe,wheretheywereheldfor3dayspriortoshipment.

ThefirstrecognizedoutbreakofMarburgvirusdiseaseinAfrica,andthefirstsincethe1967outbreak,occurredinSouthAfricainFebruary1975(Gearetal.1975)(Fig.31.2b).TheindexcaseinvolvedayoungAustraliantouristwhohadhitchhikedthroughZimbabweanddiedafteradmissiontoaJohannesburghospital.Shortlyafterwardstwonon-fatalsecondarycasesoccurred,onehisfemaletravellingcompanionandanurse(Table31.1).Again,therewasevidencethattheviruspersistedinthebody;theviruswasrecoveredfromfluidaspiratedfromtheanteriorchamberofthenurse’srighteye80daysafteronsetofillness.InJanuary1980,Marburgre-appearedinKenya(Smithetal.1982).TheindexpatientwasanelectricalengineerwhoacquiredthefatalinfectioninwesternKenya.Anon-fatalsecondaryinfectionoccurred9dayslater.Thisinvolvedadoctorwhoattendedthepatientandhadattemptedmouth-to-mouthresuscitation.In1987,anisolatedcaseoffatalMarburgdiseasewasagainrecognizedina15yearoldDanishboywhohadbeenadmittedtohospitalinKenya.Ninedayspriortotheonsetofhisdisease,healsohadvisitedKitumCaveinMountElgonnationalpark.RecentstudiesofcoloniesofR.gypriacusbatswhichinhabitthesecaveshavedemonstratedmolecularandserologicallypositiveforMarburgvirusbutthereroleintransmissionisasyetundefined(Kuzminetal.2010).PresentlyitisthoughtthatthehabitatofthenaturalhostofMarburgvirusiswithin,butnotlimitedto,theMountElgonareaandpossiblyoverlapsthedistributionofEbola.


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Fig.31.2DistributionanddatesoffilovirusoutbreaksinAfrica(a)Ebolavirusdiseaseand(b)Marburgvirusdisease.

Between1987and1998,theonlycaseofMarbugreportedwereassociatedwithlaboratoryaccidentsintheformerSovietUnionofwhichonewasfatal(Nikiforovetal.1994)outlinesthedangersassociatedwithworkingwiththeseagentsinthelaboratory.

However,in1998,thelargestnaturaloutbreakofMarburgvirusdiseasetodatebeganinnortheasternDemocraticRepublicoftheCongo(DRC).Thistime,thefocusoftheoutbreakwasatowncalledDurba(population16 000).AlargenumberofmeninthisregionworkfortheKiloMotoMiningCompany,whichrunsanumberofillegalgoldminesinthearea.TheMarburgoutbreakstartedinNovemberof1998,althoughnotreportedtoanyinternationalagenciesuntillateAprilof1999,followingthedeathofthechiefmedicalofficerintheareafromthedisease.Theoutbreakhadacasefatalityrateofapproximately83involving154casesbeforethedeclarationthattheoutbreakwasoverin2000.ThediseasealsospreadtoneighbouringvillagesparticularlyWatsa.MinershadasignificantlyhigherriskofcontractingMarburgthanthegeneralpopulationofthisarea,suggestingfrequentexposuretothenaturalreservoirofMarburgvirus(Bausch2006).

Thesizeandextentofthisoutbreakwaseclipsedatthebeginningin2004,whenaMarburgoutbreakoccurredinAngoladuringOctober.Duetocivilwarinthecountryandanon-existentpublichealthinfrastructure,recognitionoftheoutbreakwasdelayeduntilalmost6monthslater,inMarchof2005.TheoutbreakwasdeclaredoverinNovemberof2005,afternoadditionalcaseshadbeenreported(Towner2006).

In2007threecasesinyoungmales,againassociatedwithminersworkinginLeadandGoldminesintheKamwengeDistrictofUgandawasreported(WHO2007).Finallyin2008,aDutchtouristdevelopedMarburgfourdaysafterreturningtotheNetherlandsfromathreeweekholidayinUganda.Todate,thesourceoftheexposurehasnotbeenconfirmed,althoughthewomanvisitedPythonCaveinwesternUgandawherebatswerepresent(WHO2008,2009;Timenetal.2009).TheUgandanMinistryofHealthclosedthecaveafterthiscase.

Ebolavirusdisease(Africa)

Twolargesimultaneousoutbreaksofanacutehaemorrhagicfever(subsequentlynamedEbolahaemorrhagicfever)occurredinsouthernSudan(WHO1978a)andnorthernZairein1976(WHO1978b)(Fig.31.2b).ThefirstoutbreakwasidentifiedinsouthernSudaninJune,continuingthroughtoNovember1976.Therewere284cases,67inNazara,213inMaridi,3inTembura,and1inJuba.ThefocusoftheepidemicwasNazara,asmalltownwithclustersofhousesscatteredindensewoodlandborderingtheAfricanrain-forestzone.TheoutbreakinNazaraoriginatedinthreeemployeesofacottonfactorysituatednearthetowncentre.Detailedfactoryrecordsfortheprevious2yearsdidnotshowanyfatalhaemorrhagicdiseaseinNazarauntilJune1976.Atthattime,oneortwoworkersstarteddyingeachweek.BySeptember,6factoryworkersand25oftheircontactshaddevelopedthesameillness,ofwhich21died.Beforetheoutbreakdiedoutspontaneouslycaseswerereportedintwoneighbouringareas.ThefirstwasinTembura,asmalltown160kmnorthofNazara,whereanillwomanwenttobenursedbyherfamily.Beforeshedied,threewomenwhocaredforheralsodiedofthesamehaemorrhagicdisease.Noothercaseswerediscovered.Secondly,theepidemicwasdramaticallyamplifiedbythelargerhospital-associatedoutbreak(213cases)inMaridi,followingtheintroductionofapatientfromNazara.Maridi,atowneastofNazara,hadanestimatedpopulationof10,000people.Ninety-threecases(46%)acquiredtheirdiseaseinhospital,and105(52%)inthecommunity.Ofthe230staffatMaridihospital,72becameinfectedwhileatworkand41


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died.Thehighestrateofinfectionwasassociatedwithnursinghaemorrhagicpatientswho,attheheightoftheepidemic,occupiedmostwards.AfterMaridi,furthercases(onefromNazaraandthreefromMaridi)weretransferredtotheregionalhospitalinJuba.AfurtherthreepatientswereflowntoKhartoum(1,200kmnorth),wheretwodied.AnursefromJubawastheonlysecondarycaseidentifiedasaresultofthesepatienttransfers.

Overall,therewere151deaths(mortalityrate,53%)outof284cases.TheoutbreakinNazaracontinueduntilOctober,infecting67peopleofwhom31(46%)died,comparedto116(54%)inMaridi.Studieson36familieswhonursed38primarycasesindicatedthatof232contacts30(14%)developeddisease.Similarratesoftransmissionwereobservedinsubsequentgenerations,givinganoverallsecondaryattackrateof12%.BetweenJulyandOctober1979,34casesofEbolahaemorrhagicfeverrecurredintheYambio-NazaraDistrict.Fivefamilygroupsandtwoindividualsbecamecontractedtheillness.Theindexcase,acotton-factoryworker,transmittedthevirustoseveralmembersofhisfamily.Theoutbreakextendedtootherfamiliesthroughnosocomaltransmissionduringhishospitalizationandthehospitalizationofsubsequentcases.Mortalityinthisoutbreakwas65%(22deaths).Itwasunclearwhetherthecottonfactorywasthesourceoftheindexcaseofinfection.

AlsoduringSeptembertoOctober1976,alargeoutbreakofEbolahaemorrhagicfevertookplaceintheequatorialrainforestofnorthernZaire(WHO1978b).TheindexcasehadbeentouringandpresentedhimselftotheoutpatientclinicatYamkukaMissionHospital(YMH)fortreatmentofacutemalaria,andreceivedaninjectionofchloroquine.Hewasadmittedtohospital10dayslaterwithgastrointestinalbleedinganddied.Duringthefollowingweek,nineotherpatientswhohadreceivedtreatmentattheoutpatientclinicoftheYMHcontractedEbolahaemorrhagicfever.Almostallsubsequentcaseshadreceivedinjectionsorhadbeeninclosecontactwithotherpatients.Thehighestincidencewasamongstwomenof15–29years,whohadattendedantenatalandoutpatientclinicsatthishospitalandreturnedtotheirvillages.After13of17staffhadacquiredthediseaseand11patientsdied,thehospitalclosed.Themajorriskfactorprovedtobethere-useofnon-sterilizedneedles,whichwereinshortsupply.Between1Septemberand24October,therewere318knowncasesofEbolahaemorrhagicfeverwith280deaths,acasefatalityof88%.Therewereover55villagesintheendemicarea(Bumbazone),containingsome550recordedcases.Theoverallsecondaryattackratewascalculatedtobe5%,butnearer20%incloserelativesofacase.AfurthersinglefatalcasewasidentifiedinTandalaHospitalinnorthwesternZairein1977(Heymannetal.1980).StudiesintheTandalaregionrevealedtwopossibleEbolacasesdatingbackto1972,anda7%Ebolaseroprevalencerateinthelocalpopulation.

InJanuary1995,acharcoal-makernearKikwit,atowninBanduduProvince,550kmeastofKinshasa,wasthefirstfatalcaseofEbola(WHO1995a).ByearlyMarch12membersofhisfamilyhaddied.Simultaneously,aShigellaIdysenteryepidemicwastakingplaceandmaskedtheearlystagesoftheEbolaoutbreak.HospitalsbecamesourcesofinfectionduringFebruarywhenanEbolapatiententeredtheKikwithealthcentreandlatertransferredtothegeneralhospital.DuringApril,membersofaresuscitatingteambecameillafterhandlingapatientmisdiagnosedashavingtyphoid.Rapidtransmissionofunprotectedhealthworkersandotherpatientsoccurred,manycarryingthediseasebackintothecommunity.BetweenJanuaryandJune315caseshadoccurred,ofwhich244died(77%).Thefemale:maleratiowas166:149,which74%(123)femalesand81percent(121)malesdied.Provisionaldataidentified75(26%)nursesorstudentsand61(21%)housewiveswhocontractedthedisease.Twohundredandsixty-six(84%)ofthecasesresidedwithintheKikwitNorthandSouthZonesdeSanté.NocasesidentifiedoutsidetheBandunduregion.

ThegeographicdistributionofEbolaviruswidenedinNovember1994whenanon-fatalEbolahaemorrhagicfevercaseemergedforthefirsttimeinWestAfrica(LeGuennoetal.1995).IntheTaiNationalPark,Côted’Ivoire,a34yearoldethnologistinfectedherselfwhilecarryingoutapost-mortemonawildchimpanzeefounddeadwithsignsofhaemorrhages.Eightdayslater,shewasadmittedtohospitalinAbidjanforsuspectedmalaria.Astherewasnoimprovementinhercondition,shewasrepatriatedbySwissAirAmbulanceandadmittedtotheUniversityHospitalofBasel.Ashaemorrhagicfeverwasconsideredunlikely,shewastreatedwithciprofloxacinanddeoxycyclinforsuspectedGram-negativesepsis(typhoidfever),leptospirosis,orrickettsialdisease.RetrospectivestudiesisolatedtheEbolavirus.Noclinicalillnessnorseroconversionsweredetectedamong22contactpersonsintheCôted’Ivoireor52hospitalandair-ambulancestaffbasedinSwitzerland,despitethelackofanearlyEboladiagnosis.Latein1995,a25yearoldrefugeefromneighbouringLiberiawasadmittedtothehealthfacilityofGozon,Côted’Ivoire,confirmingthepresenceofEbolavirusinWestAfrica(CentersforDiseaseControl(CDC)1995c).Patientisolationandbarriernursingpreventedfurtherspreadofinfectionwithinandfromthehealthfacility.PreliminaryinvestigationofhishouseholdcontactsinthevillageofPlibo,MarylandCounty,LiberiafoundthattwomalecontactsshowedthesignsandsymptomsofearlyEbolainfection.

Zaireebolavirus(ZEBOV)hasrepeatedlycausedlargeoutbreaksinGabonbetween1994and2008(Geordes1999:WHO2003;Georges1998;Pourrut,2001),inDRCbetween2001and2005(Formenty2003)andintheDRCin1995and2007.In2007,103people(100adultsandthreechildren)wereinfectedbyasuspectedhemorrhagicfeveroutbreakinthevillageofKampungu,DRC.Theoutbreakstartedafterthefuneralsoftwovillagechiefs,and264peopleinfourvillagesfellill.TheCongo’slastmajorEbolaepidemickilled245peoplein1995inKikwit,about200milesfromthesourceoftheAugust2007outbreak(WHO2007).In2004,itresurfacedaroundGuluinUganda(Okware2002).Again,thediseasewasamplifiedinlocalhospitalsandspreadintoseveralUgandanadministrativedistricts.Therewereatleast425humancases


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and224deaths(Bitekyerezo2002).On30November2007,theUgandaMinistryofHealthconfirmedanoutbreakofseveregastrointestinaldiseasecausedbyEbolaintheBundibugyoDistrictofUganda.AfterconfirmationofsamplestestedbytheUSANationalReferenceLaboratoriesandtheCDC,theWHOconfirmedthepresenceofanewspeciesofEbolavirusthatisnownamedBundibugyo.Theepidemicendedon20February2008.Whileitlasted,149casesofthisnewstrainwerereported,and37provedfatal.(Tower,2008).Thefifthebolavirus,‘Ugandaebolavirus’(‘UEBOV’)wasdiscoveredduringthisoutbreakof2007.Ebolavirusagaincausedanoutbreakthatkilled15andinfected32peopleinsouthernDRCinJanuary2009.AngolacloseddownpartoftheirborderwithDRCtopreventthespreadofEbolaaftertheirexperiencewithMarburgvirusin2 004whichkilled227people.

Finally,therisksoffilovirusresearchweredemonstratedin12March2009,whenanunidentified45yearoldfemalescientistfromGermanyaccidentallyprickedherfingerwithaneedleusedtoinjectEbolaintolaboratorymice.Shewasgivenanexperimentalvaccineneverbeforeusedonhumans.Itremainsunclearwhetherornotshewaseverinfectedwiththevirusoriftheexperimentalvaccineprovedbeneficial.

Asinmostebolavirus-diseaseoutbreaks,itisrecognizedthatburialritualsandcaringofandclosecontactwiththesickcontributedtothespreadoffiloviruses(Gear1975).Mostoftheseoutbreaksbeganwithpeoplewhohadhuntedanimalsintheforestorfounddeadanimalsandconsumedthem.ThemechanismoftransmissionofinfectionintheEbolavirusoutbreaksismainlybydirectcontactwithinfectedbloodortissue,byverycloseandprolongedcontactwithacutelyillpatients,orbyinoculationwithcontaminatedsyringesandneedles.Transmissionthroughtheairborneroutedoesnotseemtobeafactorinthemaintenanceofanyoftheepidemics.ItisalsothoughtthatespeciallyZaireebolvirusiscausingepizooticsamongcentralchimpanzees(Pantroglodytestroglodytes)andwesternlowlandgorillas(Gorillagorillagorilla),whichmayhavecontributedramaticallytotheirpopulationdecline(Karesh2005).

Naturalreservoirs

ThenaturalreservoiroftheEbolavirusisunknowndespiteextensivestudies,butitseemstoresideintherainforestsontheAfricancontinentandintheWesternPacific.Between1976and1998,variousmammals,birds,reptiles,amphibians,andarthropodsfromoutbreakregionshavebeenstudiedtodeterminethenaturalFiolovirusreservoir.NoEbolaviruswasdetectedapartfromsomegeneticmaterialfoundinsixrodents(MussetulosusandPraomys)andoneshrew(sylvisorexollula)collectedfromtheCentralAfricanRepublic(Peterson2004).Theviruswasdetectedinthecarcassesofgorillas,chimpanzees,andduikersduringoutbreaksin2001and2003,whichlaterbecamethesourceofhumaninfections.However,thehighmortalityfrominfectioninthesespeciesmakesthemunlikelyasanaturalreservoir.

Plants,arthropods,andbirdshavealsobeenconsideredaspossiblereservoirs;however,batsarenowconsideredthemostlikelycandidate.BatswereknowntoresideinthecottonfactoryinwhichtheEbolaindexcasesforthe1976and1979outbreakswereemployed.TheyhavebeenimplicatedinMarburginfectionsin1975and1980.Of24plantspeciesand19vertebratespeciesexperimentallyinoculatedwithEbolavirus,onlybatsbecameinfected(Swanepoel1996).Theabsenceofclinicalsignsinthesebatsischaracteristicofareservoirspecies.Ina2002–2003surveyof1,030animals,whichincluded679batsfromGabonandtheDRC,13fruitbatswerefoundtocontainEbolavirusRNA(Pourrut2009).Asof2005,threefruitbatspecies(Hypsignathusmonstrosus,Epomopsfrangueti,andMyonycteristorquata)havebeenidentifiedascarryingtheviruswhileremainingasymptomatic.StudiesofEgyptianfruitbats(Rousettusaegyptiaxcus)inhabitingtheKitakaCave,UgandaisolatedgeneticallydiverseMarburgvirusRNAfromtissueanddemonstratedvirusspecificantibodies(Towers2009).Todate,Gabonistheonlycountrywherebat(Rousettusaegyptiaxcus)provedtobethereservoirsforbothEbolaandMarburgviruses.Thus,variousspeciesofbatsindicatethattheyarepotentialnaturalhostspecies,orreservoir,offiloviruses.

Restonebolavirus—unlikeitsAfricancounterparts—isnon-pathogenicinhumans.Thehighmortalityamongmonkeysanditsrecentemergenceinpigsmakesthemunlikelynaturalreservoirs.

Epizootics

Ebolavirus

SeveralfilovirusescloselyrelatedtoEbolawereisolatedin1989andearly1990fromsickordyingcynomolgusmacaquesinquarantinefacilitieslocatedinReston,Virginia,inTexas,andinPennsylvania(CDC1990a;Jahrlingetal.1990).ShipmentstoaquarantinefacilityinSiena,Italyin1992alsocontainedanimalsthatdiedwithlaboratory-confirmedEbola-likevirusinfections(WHO1992).ThemonkeysinvolvedineachepizooticimportedfromthePhilippinesandtracedtothesamemajorexportfacilities.TheidentificationofanEbola-likevirusineachfacilityledtotheterminationofallstocks,toreducetheriskofcommunityspread.IntheabsenceofanyestablishedlinkwithAfricaorAfricananimals,theepisodemustrepresentevidenceofAsianfiloviruses.Theanimalsbeingco-infectedwithsimianhaemorrhagicfevercomplicatedthefirstreportedepizooticintheUSA;however,223of1,050exposedanimalsdied.Thenaturalhostandgeographicdistributionisunknown.


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ActivetransmissionwasdocumentedatonePhilippineexportfacility(Hayesetal.1992).AntigencaptureELISAusingliverhomogenatesrevealedthat85outof161(53.2%)monkeysthatdiedwithina3monthperiodprovedpositiveforfilovirusantigen.Theincidencewascalculatedtobe24.4per100animals.Herecaptivemonkeyswereheldingangcages,increasingtheopportunityformonkey-to-monkeytransmissionofvirusbyclosecontactwithvirus-ladenbloodorbodysecretions.Thesourceoftheinfectionremainsunknown.Laboratoryexperimentationalsoshowsthepresenceofhighconcentrationsofviralantigeninpulmonarysecretions,raisingthepossibilitythattheairborneroute(Jaaxetal.1995)mayspreadthisebola-likevirus.Parenteralinoculationwithvirus-contaminatedbloodisanotherpossiblerouteduringtheepizooticsasallmonkeysweretuberculintestedandgivenantibiotics.Thecommonpracticewastoinoculatemanymonkeyswiththesamesyringeandneedle.

Serologicalevidenceoffilovirusexposurewasfoundin12(6%)of186peoplewholivedinwildlifecollectionareasorworkedinprimatefacilitiesinManila(Mirandaetal.1991).Withintheexportfacilityexperiencingtheepizootic,22%ofemployeestestedprovedpositive.Noillnesswasdocumentedinanyofthepositives.IntheRestonfacility,fiveanimalhandlerswereidentifiedashavingahighlevelofdailyexposuretosickanddyinganimals.FourwerefoundbyIFAtohavehadserologicalevidenceofrecentinfection,threeseroconvertingduringtheperiodoftheepizootic.Nofilovirusillnessdeveloped.Noneofthe16contactsofmonkeyswithEbola-likevirusimportedintoItalyshowedanyclinicalorserologicalsignsofinfection.

SincethediscoveryoftheMarburgandEbolaspeciesoffilovirus,seeminglyrandom,sporadicfataloutbreaksofdiseaseinhumansandnon-humanprimateshavegivenimpetustoidentificationofhosttropismsandpotentialreservoirs.DomesticswineinthePhilippines,experiencingunusuallysevereoutbreaksofporcinereproductiveandrespiratorydiseasesyndrome,havenowbeendiscoveredtohostRestonebolavirus(REBOV).AlthoughREBOVistheonlymemberofFiloviridaethathasnotbeenassociatedwithdiseaseinhumans,itsemergenceinthehumanfoodchainisofconcern.REBOVisolateswerefoundtobemoredivergentfromeachotherthanfromtheoriginalvirusisolatedin1989,indicatingpolyphyleticoriginsandthatREBOVhasbeencirculatingsinceandpossiblybefore,theinitialdiscoveryofREBOVinmonkeys.ThediscoveryofanumberofseropositiveabattoirworkersinthePhilippineshavingroutinecontactwiththevirusandseropositiveswinehasraisedconcernaboutthetransmissionofEbolafromanimaltoman(Barrette2009).

TheorigininnatureandthenaturalhistoryofMarburgandEbolavirusesremainunknown.Itwouldseemthatthevirusesarezoonoticandtransmissiontohumansoccursfromongoinglifecyclesinanimals.StudiesattemptingtodiscoverthesourceoftheMarburgoutbreaksinEuropeorAfrica,ortherecentEbolaoutbreakintheUSAandItaly,havefailedtouncoverthereservoir.Whatevertheirsource,person-to-persontransmissionisameansbywhichoutbreaksandepidemicsprogress.Thisinvolvesclosecontact;secondarycaseshaverarelyexceeded10%,indicatingthattransmissionisnotefficient.Nosocomialinfectionisaspecialcase;extremecareshouldbetakenwhendealingwithinfectedblood,secretions,tissues,andhospitalwaste.

Preventionandcontrol

Prevention

Withoutanunderstandingofthenaturalhistoryoftheviruses,ecologicalcontrolscapableofpreventingthesporadichumancasesthathavestartedoutbreaksandepidemicsinthepastareimpossible.Theexceptionwouldbethecontainmentofmonkeys,whichmighthavetheinfections.WhilethereisastrongsuspicionthatEbolaandMarburgdiseasesarezoonoses,thesearchcontinuesfortheoriginandreservoirhost(s)ofthevirus.

Controlstrategies

AlthoughbothMarburgandEbolainfectionsarerareevents,theyrepresentadangerousnosocomialhazard.Promptidentificationofactivecasesisessentialandisdependentuponanaccurateanddetailedhistory(DepartmentofHealthandSocialSecurityandWelshOffice1986;CDC1995;WHO1995b).Itisclearfromthefilovirusepidemicsencounteredtodatethathospitalshaveactedasthemainamplifierofthediseasetothecommunity.Therefore,itisimportantthatphysiciansworkingintheareaswherehaemorrhagicfeversoccurshouldbeawarethatthesediseasesexistandthatnosocomialspreadisahighpossibilityifnotrecognizedearlyandpatientsplacedincompleteisolationunderbarriernursingconditions.Innon-endemicareas,itisimportanttomaintainawarenessofthecurrentviralepidemiologicaldevelopmentsandthethreatofimportation.Preventionofperson-to-personspreadofthevirusisessentialtocontrol.Threeweekspriortoillnesspatientsathighestriskhavetravelledintoareaswhereviralhaemorrhagicfever(VHF)hasrecentlyoccurred;haddirectcontactwithblood,bodyfluids,secretions,orexcretionsofapersonoranimalwithVHF;orworkedinalaboratoryorfacilitythathandlestheviruses.ThelikelihoodofacquiringEbolaorMarburgisextremelylowifpatientsdonotmeetanyofthecriteria.Contactsofsuchpatientsmustbeplacedundersurveillanceandnotallowedtotravel.High-riskcontactisassociatedwithdirectcontactwithbloodorbodyfluidsfromacutelyillhumansoranimals;sexualcontactwithaconvalescentcase;orthroughlaboratoryaccidents.Thus,effectivesurveillanceofhigh-riskcontactsandisolationoffurthercasesensuresrapidcontrolofanoutbreak.Thecauseoffeverinpatientsreturningfrom


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MarburgandEbolaendemicareasismorelikelytobeotherinfectiousdisease(malariaortyphoid);therefore,evaluationandtreatmentofsuchinfectionsneedsurgentattention.

Patientcontainment

Controlofoutbreaksinendemicandnon-endemicareashasbeenassociatedwiththeintroductionofgoodhospitalandlaboratoryinfectioncontrolpractices,withtheisolationoffebrilepatients,carefulhandlingoflaboratoryspecimensandrigoroususeofglovesanddisinfectants.Thecontainmentofpatientsinplastic-filmpatientisolators(Trexlar)isfavouredintheUK(DepartmentofHealthandSocialSecurity(DHSS)andWelshOffice1986).Thesearelocatedwithinaroomhavingfilterednegativeairpressuregradients,aseparateeffluenttreatmentplantforwaste,anin-suiteautoclaveforsolidwaste,ashower,andastaffchangingroom.Manyconsiderthatthepatientisolatorreducesmanualdexterity,introducesfatigue,inhibitstheeffectivenessofintensivecareprocedures,andhinderscommunication.Ofmostconcernisthattheseisolatorsdonotreducetheriskofinjurybyanysharpinstrumentsandhavenoprovisionforresuscitation.ThissystemisnotusedinendemicareasorrecommendedintheUSA(CDC1995)sincethemainrisksareassociatedwithdirectinoculationofvirusinbloodorothermaterialandtheaerosolhazardconsideredlowrisk.Thus,itisrecommendedtoconfinepatientstoisolationinasingleroomwithorwithoutcontrolledfilteredair.Themostimportantconsiderationisstafftrainingandsupervision,theuseofglovesandmasks,andthemandatoryuseofadisinfectionpolicy.TherecommendationsissuedconcerningthemanagementofAIDSpatientsareconsideredadequateforcontainmentofFiloviruses.

TherepatriationtoSwitzerlandofanacutelyillEbolacaseoriginatingintheCôted’Ivoirein1994andMarburgcasefromUgandatotheNetherlandsin2008demonstratestheneedforvigilance,sincefilovirusinfectionwasnotconsideredordiagnoseduntilthepatienthadrecovered.Hadthenormalbarrierprecautionsnotbeenundertaken,thepotentialforspreadcouldhavebeendevastating.Filovirus-infectedpatientsshouldbeisolatedandbarrier-nursedtopreventsecondaryinfections.Handling,transportation,andtestingofclinicalmaterialcontainingahighconcentrationofvirusesshouldfollowinternationalandnationalguidelines.

Primateguidelines

Asnon-humanprimatesareknowntohaveintroducedMarburgtoEurope,andEbolatotheUSandItaly,themanagementoftransportationandquarantinefacilitiesshouldensurethatpersonnelunderstandthehazardsassociatedwithhandlingnon-humanprimates.Althoughtheriskofinfectionislow,guidelineshavebeenissuedtominimizesuchrisksinpersonsexposedtonon-humanprimatesduringtransportandquarantine(CDC1990b;WHO1990).Thoseatriskofinfectionincludepersonsworkingintemporaryorlong-termholdingfacilitiesandpersonswhotransportanimalstothesefacilities(cargohandlersandinspectors).Monkeys,particularlythoseimportedfromAfricaandAsia,arepotentialsourcesofarangeofdiseases,andsevereillnessordeathsinrecentlyimportedprimatesshouldbereportedtohealthandveterinaryauthoritiesandinvestigatedforavarietyofinfectiousagents,includingEbola.

Captivemonkeysfrequentlyheldingangcagesincreasetheopportunityformonkey-to-monkeytransmissionbyvirus-ladenbloodorbodysecretions.StudiesoftheepizooticintheUSAandexperimentalinfectionstudieshavefoundhighconcentrationsofviralantigeninpulmonarysecretions,raisingthepossibilitythatfilovirusesspreadthroughtheaerosolroute.

AlthoughthenewlyrecognizedEbolavirusfromAsiaapparentlycausesafataldiseaseincynomolgusmacaques,initialevidenceindicatesthatitsabilitytoproduceinfectioninhumansmaybelessthanthatoftheEbolaandMarburgvirusesfromAfrica.However,becauseoftheknownseverityofdiseasecausedbyothermembersoftheFiloviridae,itwouldbeprematuretoignorethepossibilityofapossiblepublichealththreatposedbytheAsianfiloviruses.FourindependentaccountsconcerningtheimportationofFiloviridae-infectedprimatesintotheUSAandEuropefromtwoareasoftheworld,AsiaandAfrica,increasetheimportanceofintroducinganinfrastructurefortherecognition,identification,andeliminationpolicestoremovethepossibilityofspread.

Thehighdegreeoftransmissibilityamongmonkeyshousedinconfinedconditionsindicatestheneedforearlyidentificationofinfectedanimals,bothtoprotectthemonkeysandtominimizetheriskofhumaninfection.Theearlydetectionoffilovirusantigenaemiaornucleicacidwouldallowidentificationofinfectedanimalsbeforetheybecomeill.Whethertheireliminationwouldpreventanyoutbreakhasyettobeproven.Atpresent,thepotentialthreatfromfilovirusantibody-positiveanimalsremainsunclear,althoughthereisnoevidencethatlatentorconstantinfectionhasplayedanyroleinmonkey-associatedoutbreaks.Improvedquarantineandanimalhandlingproceduresneedtobeuniversallyimplementedtoensurenofutureoutbreaksassociatedwithwild-caughtmonkeys.Therefore,contactbetweenmonkeysandmanshouldbelimitedandanimalhusbandrytightlycontrolled.Personnelhandlinganimalsshouldwearprotectiveclothing,includingrubberglovesandfacerespirator.Allanimalwaste,cages,andotherpotentiallycontaminateditemsshouldbetreatedwithappropriatedisinfectants.

Finally,theincreasedconcernforwildlifeconservationandlicensingofexporters/importerswillfurtherdecreasetherisk


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offilovirusspreadtoman.

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