Probability ofclassical swine fever virus introduction in the
European Union: analysis and modelling
C.J.deVos,H.W.Saatkamp andR.B.M.Huime
FarmManagementGroup,DepartmentofSocialSciences,WageningenUniversity,Hollandseweg1,
6706KNWageningen,TheNetherlands.E-mail:[email protected]
1. Introduction
Recent classical swinefever (CSF)epidemicsin theEuropean Union(EU)incurred high
economiclosses.In 1993/94Germany and Belgium wereseverelyhitbyaCSFepidemic,
217farmsbeingaffected inGermany (Kramer etal., 1995;Pittleretal., 1995)and 55in
Belgium (Laevensetal., 1998;Koenen etal., 1996;Vanthemsche, 1996).Even more
disastrouswasthe 1997/98 CSFepidemic intheNetherlands,whichaffected 429 farms,
whilemorethan 10million pigsweredestroyed preventively and for welfare reasons
(Anonymous, 1998).Thecostsofthisepidemic (i.e.direct costsand consequential lossesto
farms andrelated industries)wereestimated at US$2.3billion (Meuwissen etal., 1999).
Import ofinfected piglets from theNetherlands alsolead toamajor epidemicinSpain,99
farms being infected in 1997/98(Edwardsetal.,2000;Greiser-Wilkeetal.,2000).
Theintroduction ofCSFisacontinuing threat tothepigproduction sectoroftheEU.The
diseaseisstillpresent in somecountriesofcentral andeastern Europe(Edwardsetal.,2000).
Besides,CSFoccursinan endemic form inwild boarpopulations insomeareasof Germany,
Franceand Italy(Laddomada,2000),representing apermanent CSFvirus(CSFV) reservoir.
Thedisease can thuseasily bereintroduced intofreeregions ifnopropermeasuresaretakel
Prevention ofCSFVintroduction should therefore getthehighestprioritypossible.
Most outbreaks inthemajor CSFepidemicsmentioned aboveoccurred intheso-called
denselypopulated livestock areas(DPLAs)thathaveanaveragepigdensityofmorethan3ÓÖ
pigs/km2(Michel &DeVos,2000).Theseareascameintobeingduetoeconomic factors,
such astheavailability ofcheapfeedstuff andreasonably pricedland andthevicinityof
urban markets(Dijkhuizen &Davies, 1995;Huirneetal., 1995).Theconcentration ofpig
production in theseareas issupposed tobecorrelated withtheriskofintroduction andspread
ofepidemicdiseases(Dijkhuizen &Davies, 1995).Pigandpigfarm density are,however,
nottheonlydeterminantsintheriskofvirusintroduction.Insight intoallfactors contributing
totheriskofvirusintroduction isaprerequisite for takingpreventiveactionsthatareboth
epidemiologically effective and economically sensible,andistherefore ofutmostimportance
insupporting policy-making.
This study focuses ontheprobability ofCSFVintroduction for severalregions intheEU. The
main objective wastogain moreinsight intothemajor factors contributing tothisprobability.
Two approaches wereused:(i)aqualitative assessment thatprovidesatoolforaquick
analysisthat canbeperformed withrelatively littleinformation and (ii)aquantitative
approach using acomputermodel,thatprovidesmoredetailed insightintothefactors that
contribute totheprobability ofCSFVintroduction,but forwhich alotofquantitativedataare
needed.
Thepaper startswithanoverviewofsomerelevant definitions. Then apathwaydiagram
giving anoverview ofallpathwayspossiblycontributing totheprobability ofCSFV
introduction ispresented. This was used as the basis for both the qualitative'assessment SfirT
the computer model. Results of the qualitative assessment are given for five densely and five
sparsely populated livestock areas (SPLAs) in the EU. Model results are presented for five
EU member states.The paper concludes with discussion of the approaches used and the
results obtained.
2. Definitions
As not all definitions in the field of animal health risk analysis are standardised yet, a brief
overview of key terms used throughout this paper is given first.
Virus introduction is defined as entrance of virus into the livestock production sector of a
region free of the disease, causing a primary outbreak1. The definition of a primary outbreak
was derived from EU Council Directive 82/894/EEC: 'an outbreak not epizootiologically
linked with a previous outbreak in the same region of a member state, or the first outbreak in
a different region of the same member state' (CEC, 1982).The regions used for this
definition are areas with a surface of at least 2000 km 2 , that must be controlled by competent
authorities and at least comprise one of a certain, member state-dependent, administrative
area, e.g., provinces in Belgium, Italy and Spain, counties in the United Kingdom and Ireland
and departments in France (Council Directive 64/432/EEC, Article 2 (CEC, 1964)). Using the
EU definition of aprimary outbreak, more primary outbreaks can occur within one epidemic
Thefocus inthisarticleisonCSFVintroduction intothedomesticpigpopulationofaregion.Virus
introduction intothewildboarpopulation hasnotbeenconsidered,becauseprevention andcontrolstrategies
usedaredifferent (CEC, 1980),aswellastheeconomicconsequencesofsuchanintroduction.
ifvirusisspreadfromoneregion toanother.Thiswasthecase,for example,duringthe
1997/98CSFepidemic intheNetherlands,inwhich fourprimary outbreakswererecorded.
Introduction ofvirusisinducedby so-called pathways.Thesearethecarriersand
mechanisms that cantransmitvirusfrom aninfected toasusceptibleanimal.Pathwayscan
eitherbeexogenous orendogenous.Exogenouspathwaysarelinked withvirussources
outside theregion wheretheymight causeaprimaryoutbreak,whereasendogenouspathways
residewithin theregion affected. Theregionswhereexogenouspathwaysmaycomefrom are
called regionsoforigin,whereastheregion affected iscalled thetarget area.
3. Pathway diagram
Toobtain moreinsight intotheprobability ofCSFVintroduction, aso-called pathway
diagram wasconstructed toshow allpossiblepathways for CSFVintroduction, including
theirmain eventsandinterrelations (Fig. 1). Apathwaydiagram isatree-like approach that
provides insight intoallpossiblecausesof anadverseevent(DeVosetal.,2001).Inorder for
theadverseeventtooccur,allcontributing eventsofacertainpathwayhavetobetrue.
Assigningprobabilitiesto alleventsinthediagrammakesitpossible toestimatethe
probability ofoccurrenceoftheadverseevent.
Insert FigureJ
Thepathway diagram consistsoffour levels.Startingatthetopofthediagram,thefirstlevel
comprises thepathways forvirusintroduction intoaregion,includingboth exogenousand
endogenouspathways.Apathway canonly contributetotheprobability ofvirus introduction
ifitispresent.Theextentofpresence isexpressed inpathway-units whicharetheunitsin
which apathwayismeasured, e.g., ananimal,ametrictonofanimalproductsorareturning
livestock truck.
Atthesecond level,itisdetermined whether anypathway-units arepresent that are infected
orcontaminated withvirus.Obviously,exogenous pathwaysonly constitute arisk,ifthey
originatefroman areawherethediseaseisprevalent. Endogenouspathwaysonlyposea risk,
iftheycontain avirusreservoir. Someexogenouspathwayscanonlycontributetothe
probability ofvirus introduction, iftheyoriginate from aneighbouring area,e.g.,air currents
andbirds,pets,arthropods androdents.Thesepathwaysplay aminorroleinvirus
introduction,because theytransport thevirusoveronly shortdistances.
Atthethird level,itisevaluated whether preventiveactionssucceed indetectingand/or
inactivating thevirus.Only aselection ofpreventivemeasuresisgiveninthediagram.Most
additional preventive measuresthat canbetakenbyaregion,e.g.,testingorquarantine,can
beadded tothepathway diagram atthislevel.
Ifthevirusisstillpresent after passing thethird level,virustransfer tosusceptibledomestic
animalscanoccurbytwomainroutes:swill feeding toordirectorindirect contact with
susceptible animals.Whichrouteisrelevant dependsonthepathway for virusintroduction. ,
Virustransfer willonly result in anoutbreak ifthevirusconveyed constitutes an infective
dose.There is,however, oneexception tothisgeneral pattern:import ofaninfected live
animal,legallyorillegally, will alwayslead toanoutbreak iftheanimal survivesand
infection isnotdetected intime.Then swill feeding orcontactwith susceptible animals isnot
required tocauseaprimary outbreak, sincetheimported animalbecomespart ofthelivestojjg
population.
Foreachpathway,themain eventsleading toaprimary CSFoutbreak areshown inthe
pathway diagram.Theoretically, each event inthepathwaydiagram canbeassigneda
probability thatitwill occur.Theseareall conditional probabilities,i.e.,theprobabilityof
occurrenceofacertain event given that allpreviouseventshaveoccurred. Togivean
example,virusintroduction bythepathway 'returning livestock trucks' will onlyoccurifa
livestock truckreturnstotheregion after visiting aninfected region,ifthistruck is
contaminated withvirus,ifitisnot disinfected properly, ifitcomesintocontact with
susceptible animalsand ifthevirusdoseconveyed isatleast theminimum infective dose.
4. Qualitative assessment of the probability ofCSFV introduction into densely and
sparsely populated livestock areas
Thepathwaydiagram ofFigure 1 wasusedtoqualitatively assesstheprobability ofCSFV
introduction forfivedensely andfivesparselypopulated livestock areas intheEU.
Information aboutthepresenceofpathways(level 1 ofthepathwaydiagram)andthe
possibility ofpathwayspassing virustosusceptibledomesticpigs(level4)wasusedto
classify theregionsaccording theirprobability ofCSFV introduction.
Basic information available for eachregion ispresented inTable 1-A. Thisinformation was
used tocalculatepig and farm densityandtoderivean estimateofthenumberofpigs
exported orimported bytheregion (Table 1-B).Theestimatesderived aretheminimum
numbersofpigs imported orexported.Obviously, inmostcases thesewillbean
underestimate ofthegrossimports andexports.
Insert Tables1-Aand1-B
Table 1-B indicatesthatregionswith ahighpigdensity havelargernet importsorexportsof
pigsthanregionswithalowpigdensity. Südoldenburg (GE),Mantova(IT),and WestFlanders(BE)aremajor net importersofpiglets,whereas South (NL)and Côtesd'Armor
(FR)aremajor net exporters.Südoldenburg (GE)hasanet importoffattening pigs,whereas
South (NL),Mantova (IT),West-Flanders (BE),and Côtesd'Armor (FR)haveanetexportof
fattening pigsduetoashortageofslaughtercapacity. Regionswithahighpigdensity also
haveahigh pig farm density,with theexception ofMantova(IT)wherepigsareconcentrated
inlargeintensive farms.Thenumberofairportswithregular flights ishighest forCôtes
d'Armor (FR)whichhasfour ofthem.Thenumberoflaboratoriesworking with CSFVis
highest for Hannover(GE)which hasthree,including theEUReference Laboratory forCSF.
Thenumberofwildboarishighest for Ome(FR)with anestimated population of5,500
animals.NoCSFinfections inwild boarwere,however,detected inrecentyearsinthe
regionslisted inTable 1-A (Laddomada,2000).Swill feeding isforbidden inallbutthe
Germanregions.InGermany swill feeding isstill allowed,butonly after adequateheat
treatment. Hence,ifallregulations wereobserved,noneoftheregionsofTable 1-A would
suffer from primary CSFoutbreaks causedbyswill feeding.
Toclassify theregions ashaving alow,moderateorhighprobability ofCSFV introduction,
eightcriteriawereused (seeleft column ofTable2).Thesecriteria werebased on(i)the
(extent of)presenceofpathways and(ii)pigand farm densityand swill feeding, which are
indicators fortheprobability that CSFVwillreach susceptibledomestic pigsoncevirushas
been introduced.Ifaregionmeetsnoneoronlyoneofthecriteria,itisdenoted ashavinga
lowprobability ofCSFVintroduction. Ifaregionmeetstwoorthreeofthesecriteria, itis
denoted ashavingamoderateprobability ofCSFVintroduction,and ifitmeets four ormore,
itisindicated ashaving ahigh probability ofCSFVintroduction.Onthebasisofthese
criteria,theregions South(NL),Südoldenburg (GE),Hannover (GE),West-Flanders(BE),
and Côtesd'Armor(FR) wereclassified ashaving ahighprobability of CSFVintroduction.
South-West (NL),Mantova (IT),and Ome(FR)wereconsidered tohaveamoderate
probability ofCSFV introduction, whereastheremaining regions- the SPLAsofItalyand
Belgium- wereconsidered tohavealowprobability ofCSFV introduction (Table2).
Insert Table2
5. Computer model to assess theprobability ofCSFV introduction quantitatively
Acomputermodelwasdeveloped tocalculatetheprobabilitiesof CSFVintroduction for
individual regionsin theEUquantitatively andinmoredetail.Mainaimofthismodel isto
analysewhichpathwayscontribute totheprobabilityof CSFVintroduction foraparticular
region,theso-called target area,and from where,i.e.,whichregionsoforigin,thesepathways
originate.Furthermore,themodel providesinsight intodifferences betweentarget areaswith
regard totherankingofcausativepathways andregions,andtheirinteractions,andhence the
need fordiversification ofpreventivemeasures.
5.1.Modellingapproach
Themodel calculates theprobability ofCSFVintroduction intothedomesticpigpopulation
ofatarget areabydifferent pathways(seeFig. 1).Theprobability ofvirus introductionby
endogenouspathwaysdependsonlyonthesituation inthetarget area,whereastheprobability
ofvirusintroduction byexogenouspathwaysdependsonconditionsintheirregionoforigin
aswell asinthetarget area.Mostprobabilities calculated inthemodel arevery low,asthey
arecalculated perepidemicineachregion oforiginand separately for each exogenous
pathway.Therefore, thescenariopathway approachwasused asmodelling technique,andnot
simulation,because itrequiresrelatively littlecomputing timeandcan easilycalculate
extremely lowprobabilities (Vose, 1997).Themodelwasconstructed inMicrosoft Excel97
with theadd-inprogramme @Risk 4.0.5 (Palisade corporation).
Foreachpathway inthemodel,ascenario treewasconstructed inwhichthesequenceof
eventsthatultimately leadstointroduction ofCSFVintothedomesticpigpopulation ofthe
targetarea isdetermined (Milleret al., 1993).Only thoseeventsthat aredecisiveinwhether
aninfected pathway-unit will transmitvirustosusceptible animalswereincluded inthe
scenario trees.Eachevent inthescenariotreeswasassigned aprobability that itwill occur.
Thesewereallconditional probabilities.TogettheprobabilityofCSFVintroductionbya
certain pathway,allprobabilities alongitsscenariotreeweremultiplied.Thescenariotrees
fortheexogenouspathwayswerecalculated separately for eachregionoforigin.Combining
theoutcomeofall scenariotreecalculations gaveinsightintotherelativecontributionof
regions andpathwaystotheprobability ofCSFVintroduction for thetargetarea.
Calculations wereperformed forfiveEUmemberstates,i.e., Germany, France,Italy,the
Netherlands and Belgium.Thesearetheso-called targetareas.All EUmemberstateswere
included in themodel aspossibleregionsoforigin.Nothird countries wereincluded.
5.2. Input
5.2.1.OccurrenceofCSF
CSFisnotendemicinthedomesticpigpopulation oftheEU,exceptfor theisland of
Sardinia,Italy(Anonymous, 1997).Thediseasesituation withregard toCSFintheEU
member stateswasobtainedfromtheAnimal DiseaseNotification System (ADNS).Thisisa
computerised databaseoftheEUinwhich allprimary andsecondary outbreaksofhighly
contagious animaldiseasesarerecorded.ADNSdoes,however,notprovide information on '
linksbetweenoutbreaks andhencethenumberofCSFepidemicsthatoccurred inthe
member statescould notdirectly bederivedfromthisdatabase.Therefore, thenumberof
regionsexperiencing atleastoneprimaryoutbreak wasused toestimate theaveragenumber
ofepidemicsperyear.Dataoftheperiod 1990-1999wereused,becausefrom1990onwards
massvaccination against CSFwasnolongerapplied intheEU(Terpstra &DeSmit,2000).
Forthis 10-yearperiod,theminimum, average andmaximum numberofregionswith
primary outbreaksperyearisgiven inTable 3.Theaveragenumber wasused astheexpected
numberofepidemicsperyear inthemodel calculations.Forthosemember statesthatdidnot
suffer from CSFatallduring thisperiod,theexpected number ofepidemicsperyearwasset
at0.095usingtheexponential distribution (Vose, 1997):
Epidemicsyear= 1 - exp(-x/ß)
(1)
withx=timeintervalused for thecalculations (i.e.1year)and ß=minimum intervalbetween
twoepidemics(i.e. 10year).This isthehighestpossiblevalue,sinceitassumesthat (i)the
event ispossible and(ii)itdidoccurbefore thefirstmoment ofobservation andwill occur
again immediately after the lastmomentofobservation, i.e.,in theeleventh year (whichis
2000).
Insert Table3
Furthermore,thediseasesituation inthewildboarpopulationsofthetarget areaswas
considered.CSFisendemicinpartofthewildboarpopulations ofGermany,FranceandItaly
(Laddomada,2000).Theprevalenceofinfection variespermetapopulation ofwildboarand
ismonitored by samplingprogrammes (e.g.Eibers&Dekkers,2000;Crucièreet al.,1998;
Kern, 1998).Theregionsinwhich infected wildboarroam aretheBundesländerofLower
Saxony,Mecklenburg-Vorpommernand Brandenburg inGermany,thedepartmentsof
MoselleandBas-Rhin inFrance,andtheprovincesofNuoro,Sassari andOristano(all onthe
island of Sardinia)andVareseinItaly (Laddomada,2000).
5.2.2. Pathways inthemodel
Inthepathway diagram ofFigure 1 allpathwaysthatpossibly contributetotheprobabilityof
CSFVintroduction wereincluded. Aselectionofthesepathwayswasmadefor inclusionin
thecomputer model forvirus introduction onthebasisoftwocriteria:(i)expected
importance for CSFVintroduction on thebasisofhistorical data and scientific literatureand
(ii)availability ofknowledge and data toquantify theunderlying probabilities.
Themajor routes forCSFVintroduction in theEUsince theprohibition ofmassvaccination
werefeeding ofimproperlyheated swill,directorindirect contact with wild boarand animal
movements (DeVosetal.,2000;Fritzemeier etal.,2000).Information from ADNSgave
similarresults,indicating thatpurchaseofanimals,waste food feeding, and spread by
fomites2 caused themajority ofprimary CSFoutbreaks for which theorigin ofdiseasewas
given inADNS(DeVoset al.,2001).
Therefore, theexogenouspathway importofbatch ofdomesticanimalsand the endogenous
pathway wildlife wereincluded inthemodel forvirusintroduction. Furthermore,thepathway
importofanimalproducts forhuman consumption wasincluded,asitisoneofthe major
routesthatmight contributeto(illegal)swillfeeding. Illegal importsofanimalsandanimal
productsmight evenbemoredangerous with regard totheprobability ofCSFV introduction,
becausetherearenochecksonwheretheseimportscomefrom and theirdiseasestatus.These
pathways were,however,not included inthemodel,asnodatawereavailableontheir
numbers.Thepathwayreturning livestock truckswasincluded intothemodel,becausedata
couldbederivedfromthetotal numberofanimalsexported and expertsconsidered ittobean
importantriskfactor for theriskfor CSFVintroduction intotheNetherlands (Horst etal.,
1998).Although CSFVcanbetransmitted potentially overlongdistancesbydistribution of
virus-contaminated semen (DeSmit,2000),thepathway geneticmaterial wasnot included in
themodelduetolackofdata.All otherpathwaysdisplayed inthepathway diagram werenot
included intothemodel astheywereconsidered tocontributeonlymarginally tothe
probability ofCSFVintroduction andhardly anydatawereavailable for quantification.
2
Spreadby fomites isall virus spreadcaused byobjects that arecontaminated with thedisease agentandhence
covers those indirect contactsbetween animals thatare notincluded inothertransmission routesdistinguished in
ADNS (Laddomada,personal communication). Italso includes spreadby wild boar(Pittleret al., 1995).
12
5.2.3. Occurrenceofpathways
InTable4,dataontheoccurrenceofpathways included inthemodel aregivenfor the five
target areas.Imports from and exportstoallEUmemberstatesareshown.Inthemodel,these
numbersweresubdivided according theirregionsoforigin.Thenumbersofpigsimported
and exported weredivided bytheaveragebatch sizetoget estimatesofthenumberofbatches
ofdomesticanimalsimported andreturning livestock trucks,respectively.
Insert Table4
Germany isamajor importer ofpigs,whereastheNetherlands isamajor exporter.Italy
hardly exportsanypigs.Withregard toporkproducts,itcanbeseenthatmosttradeisin
fresh andchilled products.The wildboarpopulationsofGermanyandFrancearemuch
biggerthanthoseoftheNetherlands and Belgium. ForItalynodataonthenumberofwild
boarin thecountrywereavailable.In Germany, wildboararesprea"dalloverthecountry,
whereasintheothercountries theyaremoreregionallydistributed (Anonymous, 1999).
Thepathways weredivided into subgroups toperform themodel calculations.Theimports
and exportsofpigsweresubdivided intothreecategories,i.e.,piglets,breedingpigsand
fattening pigs.Itwasassumed that therisksofCSFVintroduction mightdiffer between these
categories.Fattening pigsarebrought toslaughterhouses, whereaspigletsandbreeding pigs
will becomepartofthepigpopulation in thetargetarea.Furthermore,itwasassumed that
morepreventivemeasureswillbeinusefor theimportofbreeding pigsthanpiglets.The
import ofporkproductswassubdivided intofour categories,i.e.,fresh orchilled, frozen,
non-heat treated,andheat treated pork products,because theprobability that CSFVwill
survivematuringandprocessing differs betweenthosecategories.CSFVcansurviveupto
4,5yearsinfrozen pork products (FarezandMorley, 1997)anduptoseveralmonthsin fW,
orchilled porkproducts(Terpstra, 1991; 1986).Innon-heat treatedporkproducts,i.e.,saltad.
inbrine,smoked ordried, CSFV cansurviveuptothreemonths(Terpstra, 1986).Inheattreatedproducts,CSFVwill not surviveifthecombination oftemperatureanddurationof
heattreatment was sufficient.
5.3. Calculations
Themodel calculationsweresubdivided intothreemaingroups,i.e.,regionsoforigin,
exogenouspathways,and endogenouspathways.
5.3.1.Regionsoforigin
Thisgroupcontainsall calculations ofparameters that arerelated totheCSFsituationinthe;
regionsoforigin,e.g., theannual numberofCSFepidemics,thelength oftheseepidemics,
thelength oftheirhighriskperiod (HRP),i.e.,theperiod from first infection withthevirusjp
first detection (Horstet al., 1998),thecumulative incidenceofdiseaseintheregion,etc. The
valuesoftheseparameters willvary from yeartoyearandepidemictoepidemicdueto
inherentrandomness.Averagevalueswereused inthecurrentmodel calculations.
5.3.2. Exogenouspathways
Thisgroup containsallcalculations for theprobability ofCSFVintroductionbyexogenous
pathways.Thecalculation ofthisprobability isperformed infour steps.Inthefirststep,the
probability that asinglepathway-unit will causeCSFV introduction intothetarget areais
calculated,given that CSFVispresent intheregionoforigin.Thescenariotreesdescribedin
gection5.1. areusedinthisstep.Pointofdeparture in thescenariotreesisthat CSFVis
presentintheregionoforigin.Thethreemaineventsthat canbedistinguished inallscenario
treesare:
isthepathway-unit infected orcontaminated withCSFV?
istheinfection orcontamination detectedoreliminated bypreventive measures?
doesthe infected orcontaminated pathway-unit comeintocontact with susceptiblepigsin
thetargetarea andtransmit an infective viral dose?
Inthesecond step,theprobability that CSFVisintroduced byaparticularpathwayis
calculated,combining theprobability ofstep 1 withthetotal numberofpathway-unitsgoing
from theregionoforigin tothetarget areaduring theperiod thatCSFV ispresent inthe
regionoforigin inabinomial distribution (Vose,2000).Steps 1 and2arerepeated for all
exogenouspathways inthemodel.Inthethird step,theprobabilities ofstep2aresummedto
obtain theoverall probability ofCSFVintroduction intothetargetareaduringanepidemicin
theregionoforigin.Inthefourth step,theprobability ofstep3ismultiplied withthe
expected numberofCSFepidemicsintheregion oforigin toobtaintheannualprobability of
CSFVintroduction intothetarget areafrom thisparticularregion oforigin.Thiswhole
procedureisrepeated for allregionsoforigin inthemodel.Aschematicrepresentation ofthe
stepscanbefound inFigure2.
InsertFigure2
Thecalculations for thepathway 'import ofbatch ofpiglets'aredescribed inmoredetail to
illustratethemodelcalculations inthefirst twosteps.Thescenariotreeused instep 1 isgiven
inFigure3.Thefirstevent inthisscenariotreeiswhetherthebatchofanimals transported
from theregion oforigin tothetarget areacontainsinfected piglets.Thisprobability wasset
15
equal tothecumulative incidence (CI)ofdiseaseintheregion oforigin.Thesecondevent is
whether theinfected animalswill bedetected bypreventive measures taken intheregionof •
origin, such asclinical inspection ofpigsbefore issuing ahealth certificate.Thisprobability
wasset equal tothesensitivity ofpreventivemeasures(Sereg).Thethird event iswhetherthe
infected animalswillbedetected by preventivemeasurestakeninthetarget area.This
probability wasalsoset equal tothesensitivity ofpreventivemeasures (Sela).These
sensitivities depend on thekind ofpreventivemeasurestaken and thequalityofveterinary ,
services.Theirvaluescanbechanged inordertocalculate theeffect ofmoreor different
preventive measures.Inthis scenario tree,noeventwasincluded fortheprobabilityofr.
contact with susceptiblepigsand transmission ofaninfective viral dose,because importofan
infected pigletwillalwayslead to aprimary outbreakiftheinfection isnotdetectedtimely
and thepiglet isbrought ontoafarm inthetarget area.Theprobability that abatch ofpiglets
causes CSFVintroduction ifcoming from aregion whereCSFV ispresent ishencecalculated
by:
Pbatchofpigie,s= CI * ( 1 - S e r e g ) * ( 1 - S e u )
'(2)
Insert Figure3
Inthesecond steptheprobability that thepathway importofbatch ofpigletscausesCSFV
introduction iscalculated by:
"pathway batchofpiglets ~ » ~ ( ' ~""batchofpiglets )
with n=number ofbatchestransported during theperiod that CSFV ispresent.
*• '
Theprobabilities used in the scenariotreemightbedifferent fortheHR? and theremainder
oftheepidemic(PostHRP).Therefore Pbachofp.giœwillhavedifferent values for theHRPand
PostHRPand thecalculationshavetobeperformed separately for eachperiod andthen
i
added.
5.3.3. Endogenouspathways
Thisgroupcontains all calculations for theprobability ofCSFVintroduction by endogenous
pathways.Onlythepathwaysdirect and indirectcontact with wild boarwereincluded inthe
model(asexplained before). Thethreemain events inthescenario treesfor thesepathways
are:
- isanindividual wildboar infected with CSFV?
- doesthiswildboar comeintocontact withsusceptible domestic pigs?
- isaninfective viral dosetransmitted tothosepigs?
Toillustratethemodelcalculations for endogenous pathways,thescenariotree for the
pathwaydirect contact with wildboar isgivenin Figure4.Theprobability ofinfection (INF)
wasestimated using resultsfromserological surveys (e.g.Eibers and Dekkers,2000;Kern,
1998).Theprobability ofdirect contact with susceptiblepigs(CSAdlrcct)wasestimated using
information onthegeographical distribution ofwild boarand domesticpigproduction,
whetherwildboararerestricted intheirmovementsby,for example, fences,andthe
proportion ofpig farms withoutdoor facilities.Theprobability oftransmitting an infective
doseifdirect contact occurs(IDdino)wasassumed toberatherhigh and therefore setat0.9.
Theannual probability of CSFV introduction bydirect contact with asinglewildboaris
hencecalculated by:
17
Pboar=INF *CSAd,rœ,*IDdlrecI
(4)
Insert Figure4
Toget theannual probability ofCSFV introduction by thispathway, thisprobability isthen
combined with thetotal numberofwild boar inthetarget areausing abinomial distribution
(Vose,2000):
^pathway boar — I ~ ( I — rboar /
withn=total numberofwildboar inthetarget area.
5.4. Results
Theannua!probabilities ofCSFV introduction for thetarget areas aregiven inTable5.
Results aregiven for the exogenouspathways and separately for theendogenous pathways ..
direct and indirect contact with wildboar.Theannual probability ofCSFVintroduction by .
exogenouspathways ishighest for Germany with0.2.Germany can thus expectCSFV
introduction byexogenous pathwaysonaverageonceperfiveyears.For theothertarget
areastheannualprobability ofCSFV introduction byexogenous pathways isabout0.05.
They can thusexpect CSFV introduction byexogenous pathwayson averageoncepertwenty
years.Theannual probability of CSFV introduction duetodirect orindirect contact withwild
boariszero for theNetherlands and Belgium,asnoinfected wildboarpopulationsare
present.Theprobability that Germany and Italy will experience CSFV introduction dueto
\P)
eitherdirect orindirect contact with wildboar isveryhigh.This indicatesthatitmight
happen almost everyyearoreven several timesperyear.
Insert Table 5
5.4.1.Moredetailedresultsfor exogenouspathways
Theannual probability ofCSFV introduction byexogenouspathways isdetermined bythe
regionsoforigin (all EUmemberstates except thetarget area)and theexogenouspathways
included inthemodel.Figure5gives insight intothemain regionsoforigin contributingto
thisprobability for thetarget areas.Intheleft column agraph isdisplayed for each target area
inwhichtheannual probability ofCSFVintroduction isshownperregion oforigin. Inthe
right column alsoagraph isdisplayed for each target area,but inthesegraphstheprobability
ofCSFVintroduction during aCSFepidemic intheregion oforigin isshown.Togivean
example,theannual probability that CSFVisintroduced from theNetherlands into Germany
isalmost 0.1 (left uppergraph),whereastheprobability thatCSFVisintroduced into
Germany duringanepidemic intheNetherlands is0.16(right uppergraph).Theprobability
perepidemic ishigherthantheprobability peryear,astheexpected numberofepidemicsin
theNetherlands islessthan 1 (Table3).
InsertFigureS
Ingeneral,theNetherlands,Belgium and Germanycontributemosttotheannual probability
ofCSFVintroduction into thetarget areas(left column ofgraphs).Theprobability that CSFV
isintroduced intooneof thetarget areasduring asingle epidemic inGermany is,however,
low ifcompared with epidemicsin theNetherlands and Belgium (right column ofgraphs).
19
Therelatively high annual probability that CSFVis introducedfromGermany isthusmainly
due tothehigh averagenumberofepidemics peryearinthisregion oforigin. Furthermore,it
canbeconcluded that aCSFepidemic inLuxembourg constitutes aconsiderableriskof
CSFVintroduction for Belgium and France, whereas anepidemic in Denmark constitutesa
considerableriskofCSFVintroduction for Germany,FranceandItaly.
Figure6gives anoverview oftherelativecontribution ofexogenouspathwaystotheannual
probability ofCSFV introduction by exogenouspathwaysinto thetargetareas.Ingeneral,the
pathwayscontributing most are importofpiglets,returning livestock trucks andimportof
fresh orchilled pork products.Theirrelativecontribution differs pertargetareaand depends
bothon thenumberofpathway-units present (seeTable4)and theprobability ofCSFV
introduction perpathway-unit. Thelatter is,for example,quitehigh for pork products
imported intoGermany incomparison totheother target areas,asthisistheonlytarget area
whereswill feeding isstill alluwed(seeTable 1-A).Thisexplainstherelativelyhigh
contribution ofthispathway totheannual probability ofCSFV introduction intoGermany.
On thebasisof thenumberofpathway-units present only,onewould expect amuchbigger
contribution oftheimportofpigletsand fattening pigs.ForItaly,therelativecontributionof
imported pork productstotheprobability ofCSFV introduction isalsohigh,which ismainly
duetothe largeamountof fresh and chilled porl products imported.FortheNetherlands,
returning livestock truckscontributemost totheannualprobability ofCSFV introduction.
This isduetothehugenumber ofpigsexported.Belgium alsoexportsquitealotofpigs.
Returning livestock trucksdo,however, notcontributemuch tothe annua!probabilityof
CSFVintroduction, asin Belgium almost 60%ofthefarmers disinfects incoming vehicles reducing theprobability ofCSFV introduction perpathway-unit -, whereas inallother
member states,thispercentagevaried between 0and 12.5% (data obtained froma
20
questionnaire conducted during theEUResearch Project FAIR5-PL97-3S66,refer to Italian
paper).ForBelgium theimport ofpigletsisthemost importantpathway which isexplained
by thelargenumberofpiglets imported. ForFrance,bothimportofpigletsandpork products
contributed alot totheannual probability of CSFV introduction.
Insert Figure6
5.5.Sensitivityanalysis
Sensitivity analysiscan indicate theimpact ofinputparameters onmodel outcome.Forthis
purpose,thevaluesofsomeimportant inputparameters werechangedbyincreasing and
reducing them with afactor 2.Theparameters changed were(1)theaveragelength ofthe
HRPper epidemic intheregionsoforigin,(2)the numberof lifepigsimported,(3)the
numberoflifepigsexported andhencethenumber ofreturning livestock trucks,and (4)the
probability that swill feeding ispractised, which affects boththeprobability ofCSFV
introduction byimportofporkproducts andby indirect contactswith wild boar. Furthermore,
theprobability ofCSFV introduction for thehypothetical situation thatnoswill isfed atall
wascalculated. Resultsofthe sensitivity analysis for theprobability ofCSFVintroductionby
exogenouspathways arepresented inTable6and for theendogenous pathway indirect
contactwithwildboarinTable 7.The sensitivity analysisperformed did not changethe
probability ofCSFV introduction by direct contact withwildboar.
Insert Table 6
Table6givestherelativechangeoftheprobability ofCSFVintroduction byexogenous
pathways.Theeffects ofchanging the abovementioned parameters differ largelybetween l
target areas.Theimpact ofchanging the averagelength oftheHRPintheregionsoforigin
wasbiggest for theNetherlands and Belgium.Theimpact of changing thenumberof
imported life pigs wasbiggest for Belgium, whereas theimpactofchanging thenumberof
exported life pigswasbiggest for theNetherlands.Thisisinaccordance withtheresults
presented in Figure6,showing that importofpigscontributes mosttotheprobabilityof
CSFV introduction intoBelgium and returning livestock truckstotheprobability ofCSFV.
introduction intotheNetherlands.Theimpactofchanging theprobability ofswill feeding
washigh for Germany, Franceand Italy.
Ingeneral,theprobability ofCSFV introduction byexogenous pathways increased whenthe
valuesoftheinputparameters weremultiplied by2,and diminished when thesevalueswere
multiplied by0.5.Theonlyexceptions arethe changesinprobability ofCSFV introduction
for Germany and Italywhen reducing theaveragelength oftheHRP intheregionsoforigin.
Thisisdue tothefact that thetotal length oftheepidemic wasnot changed inthiscalculation
and that therefore theprobability ofCSFV introduction by import ofporkproductsduringthe
PostHRP wasincreased asthePostHRP lasted longer. Import ofpork productswasthemajor
pathway contributing totheprobability ofCSFV introduction for thesetarget areas(Fig.6).
Insert Table 7
Table 7givestherelative changeoftheprobability ofCSFV introduction byindirectcontact
with wildboar whenchanging theprobability that swill feeding ispractised.This increasesor
reduces theprobability of indirect contact per individual wildboar.Theimpactofchanging
22
thisinput parameter waslargest for FranceandItaly.ForGermany italsohad impact,butdue
tothe largewild boarpopulation present inthiscountry,theannual probability ofCSFV
introduction duetoindirect contact with wildboarwaschanged toalesser extent. Indirect
contactwith wildboardidnot constitute ariskofCSFVintroduction for thedomesticpig
population intheNetherlands and Belgium andhencechanging theprobability ofswill
feeding had noimpact onmodel outcome for thesetargetareas.
6. Discussion and conclusion
6.1. Pathwaydiagram
Insight intoall factors contributing totheriskofCSFV introduction isneeded todecideon
preventiveactionsthat arecost-effective, i.e.,achieveconsiderableriskreductionat
reasonable costs.Inthisstudyboth aqualitative andquantitative approach wereusedto
estimatetheprobability of CSFV introduction for several regions inthe EUandtoevaluate
which factors contribute most totheprobability ofCSFVintroduction. Both approaches were
based onapathway diagram especially constructed for CSFVintroduction intoregionsofthe
EUunderanon-vaccination policy.
Constructing such apathway diagram providesmoreinsight intoallpossiblepathwaysand
events contributing totheoccurrence ofanadverseevent.Therefore itisrecommended as
partofhazard identification, which isthefirststepinriskanalysis(Wooldridge et al., 1996).
Themorepathways involved,themorecomplex thediagrambecomes.Therefore onlythe
main events leading totheoccurrenceofaprimary CSFoutbreak were involved inthe
23
pathwaydiagram ofFigure 1.Scenario treeswereusedtodescribe eachpathway inmore
detail.
6.2.Qualitative assessment oftheprobabilityo/CSFV introduction intodenselyandsparsely
populatedlivestockareas
Thequalitative assessment oftheprobability ofCSFVintroduction into DPLAs and SPLAs
demonstrated that DPLAsgenerally had ahigherprobability ofCSFVintroduction than
SPLAs,although thiscould notbeattributed topigdensity only.Theresults shouldbe
interpreted with care,because not for allpathways in thediagram information ontheir
presence wasavailable.Furthermore, thecontribution ofpathwaystotheoverall probability
of CSFV introduction will differ, but itwasnotknown towhat extent..Somepathwaysplaya
moreimportant roleinintroducing CSFVtoaregionthan others.ThecriteriaofTable2
were,however,given equal weight inthequalitativeassessment.Therelativecontributionof
thepathwayswill alsodiffer perregion,becauseitdependson thenumberofpathway-units
present,theregion oforigin ofthepathway-units and theiruse.Horst etal.(1998)obtained
expert estimatesoftherelative importance ofpathways for CSFVintroduction.Thesewere,
however, specifically for CSFV introduction into'heNetherlands and could therefore notbe
used for different European regions.Toestimatetheprobability ofCSFV introduction for
regionsinthe EUmore adequately,quantitative information on thepresence ofpathwaysand
theirmain events isthus necessary.
24
6.3. Computer model to assess theprobability of CSFV introduction quantitatively
The computer model used to estimate the probability of CSFV introduction quantitatively
gave much more detailed insight into the factors determining this probability for a target area.
It shows which regions of origin and which exogenous pathways contribute most to the
annual probability of CSFV introduction by exogenous pathways and gives estimates of the
probabilities of CSFV introduction by wild boar separately. This information is very useful
for policy-makers as it helps to set priorities for preventive measures. The impact of
preventive measures can be estimated by the computer model as well by changing relevant
input parameters.
6.3.1. Modelling approach
The computer model developed has a clear structure. Calculations were subdivided into three
main groups, which makes it easy to add or change input parameters. For each target area
results can be obtained as aggregates (probability of CSFV introduction per year), but also
separately for each combination of exogenous pathways and regions of origin.
Not all pathways that might contribute to theprobability of CSFV introduction could be
included in the model. The model structure is,however, such that additional pathways can
easily be included ifnew information and data would become available. Some of the
pathways that were not included are considered to contribute only marginally to the
probability of CSFV introduction, e.g., import of manure, birds, pets, arthropods and rodents,
air currents and laboratories. Others might contribute considerably to the probability of CSFV
introduction, but no quantification was possible. This was the case for, e.g., import of genetic
material, illegal imports, tourists and professional people. To get a more comprehensive
25
overview ofthemajor causingpathways oftheprobability ofCSFV introduction intothe
target areas,theircontribution totheprobability of CSFV introduction maybeestimated
qualitatively.
Nothird countries wereincluded in themodel asregionsoforigin.Therefore their
contribution totheprobability ofCSFVintroduction for thetarget areascould notbe
calculated. Inordertoincludethird countries intothemodel without anexponential increase
in thenumberofcalculations,third countries could best beclustered taking intoaccount their
geographical situation and disease status withregard toCSF(e.g.endemic, free with
vaccination, free without vaccination).
Formost regionsoforigin,i.e.,EUmember states,theexpected number ofCSFepidemics
peryear islessthan one.For Germany and Italy,however, theaveragenumberofepidemics
peryearoverthelast ten years exceedsone(Table3).Simply multiplying theprobability per
epidemic with theexpected number ofepidemics instep4ofthecalculations for exogenous
pathways might inthiscaselead toanoverestimateoftheannualprobability ifthetotal
epidemic period (which alsodependson theaveragelengthoftheepidemics) exceedsayear.
Therefore the annual probabilities ofCSFViitroduction intothetarget areas from these
regionsoforiginsmighthavebeen overestimated bythemodel.Thecontribution ofItalyto
the annual probability ofCSFV introduction for thetarget areas wasratnersmall,but the
contribution ofGermany wasquitelarge,mainly duetothehigh averagenumberof
epidemicsperyear(see Fig.5).
The target areas for which model calculations wereperformed were EUmember states,and
not densely and sparsely populated livestock regions.Calculating theprobability ofCSFV
26
introduction for regions in theEUappeared tobeimpossibledueto lackofdata.Itwastried
toderivedata on importsand exportsoflife animalsperregionfromtheanimal movement
system (ANIVIO),but thesedata werenot readily available.Furthermore,dataontheanimal
movements within the memberstates areneeded toperform model calculations atregional
level.For thispurpose,national identification and recording systems(I&R)shouldbeused,
but data from such systemswerenot available inall EUmember states.Estimatingthe
probabilities for the scenario trees isalsomuchmoredifficult atregional level.
6.3.2. Results
Theannual probabilities ofCSFV introduction by exogenouspathwayswerequitelowif
compared withexpert estimates (Horst etal., 1998).Alsocomparing themodelresultswith
theaveragenumberofregionswith primary outbreaks inTable3,suggeststhat themodel
underestimates theprobability ofCSFV introduction by exogenouspathways,although for
Germany, France,and Italy wild boarmight alsocontribute considerably totheprobability of
CSFV introduction.Theprobability ofCSFVintroduction bydirect and indirect contactwith
wild boar wereindeed quitehigh,especially for Germany and Italy.This isinaccordance
withreality,asmanyprimary outbreaks inthesecountriescanbeattributed todirector
indirect contactswith wildboar.Fritzemeier etal.(2000)concluded that 59%ofallprimary
outbreaks inGermany in theperiod 1993-1998,which wereabout 90,wereduetodirector
indirect contactswith infected wild boar.And manyoftheCSFoutbreaks inItalyreported to
ADNSwereintheinfected regionsofSicilia.
Mostprobably themodel underestimates theprobability ofCSFV introduction byexogenous
pathways.Itshould bekept inmind thatnot allpathwayscontributing totheprobabilityof
CSFV introduction were included in themodel and neitherthird countries.Absolutevaluesof
27
model outcomeshould therefore notbeconsidered astruevaluesfortheprobability ofCSFV
introduction.Themodel can,though,beused torank thetargetareas for theirprobabilityof
CSFV introduction.Theultimate aimofthemodel wasnot togiveexact estimatesofthe
probability ofCSFV introduction,buttogainmore insight intothepathways andregionsof
origin contributing most tothisprobability.Theprobability ofCSFV introductionby
exogenouspathways was,for example,much higher for Germany than for theothertarget
areas.And although Germany isimporting millionsof life pigs,thispathwaycontributed less
totheprobability ofCSFVintroduction than theimport ofpork products (Fig.6).Analysing
themodel output explainsthat this isduetothefact that swill feeding isstill allowed in
Germany.
Thecontribution ofimport ofpork productstotheannualprobability ofCSFVintroduction
for thetarget areas wasratherhigh,especially for Germany and Italy(Fig.6).This isnotin
accordance withhistorical dataonthemost important sourcesof CSFV introduction (seee.g.
DeVosetal.,2000;Fritzemeier et al.,2000).Itmightbethat someofthe underlying
probabilitiesused tocalculatetheprobability ofCSFV introduction bypork productswere
estimatedtoohigh. Import ofinfected porkproductscan,however, easily leadtoCSFV
introduction if fed asswill.Thiswas,for example, seen intheCSFepidemics intheUnited
Kingdom in 1986and2000(Sharpe et al.,2000;Williams&Matthews, 1988).
6.3.3. Sensitivity-analysis
Sensitivity analysiswasperformed toget insight intothe impactofinputparameterson
model results.Only someofthemost important inputparameters werescreened. Further
sensitivity analysis canbeperformed toestimatethe impact ofpreventive measuresonthe
probability ofCSFV introduction for thetarget areas.Figures 5and 6alreadygiveagood
28
indication of theregions oforigins and exogenouspathwaysatwhichpreventive measures
should bedirected.Themodel providesalldata tomakemoredetailedpicturesofthe
exogenouspathwayscontributing most to theprobability ofCSFV introduction perregionof
origin.Prevention ofCSFVintroduction can eitherbereached bychanging (i)theCSF
situation intheregionsoforigin,(e.g.the averagenumberofepidemicsperyear, thelength
of theHRP,thenumberofinfected premises),(ii)thenumberofpathway-units coming from
certain regionsoforigin,or(iii) thepreventive measurestakentoreducetheprobability of
CSFVintroduction perpathway-unit. Themodel can provide information onwhich typeof
measures willbemost effective. Inordertocalculate thecosts and benefits ofsuchmeasures,
alsotheir impacton thespread of CSFVonceintroduced intoatarget area should betaken
intoaccount. Forthispurpose simulation modelscanbeused (e.g.Jalvingh etal., 1999;
Saatkampetal., 1996).
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36
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Table3
The minimum, average and maximum number of regions peryear in eachcountry that experienced
primary CSF outbreaks for the period 1990-19«0 (source: ADNS)
Countries
Minimum
Average
Maximum
Germany
2
10.2
25
France
0
0.5
2
Italy
0
2.8
6
The Netherlands
0
0.6
4
Belgium
0
0.4
!
Luxembourg
0
0
0
United Kingdom
0
0
0
Ireland
0
0
0
Denmark
0
0
0
Greece
0
0
0
Spain
0
0.7
5
Portugal
0
0
0
Austria
0
0.2
I
Finland
0
0
0
Sweden
0
0
0
Table4
Quantification orpathwaysincluded inthemodelfor virusintroduction
The
Germany
France
Italy
Netherlands
Belgium
1,416,941
283,049
306,213
31,735
702,767
1
Import ofpigs(numbers}
Piglets
Breedingpigs
132,633
14,805
11,753
16,319
61,418
Fatteningpigs
1,261,402
164,555
715,212
390,452
68,494
684,326
177,581
1,773
1,633,211
84,531
Breedingpigs
5,484
64,456
18,545
107,770
11,923
Fatteningpigs
371,897
72,106
7,749
1,427,590
1,012,768
Fresh/chilled
725,832
296,606
633,062
68,997
83,836
Frozen
114,365
97,759
73,167
40,759
19,038
Non-heattreated
32,380
60,150
8,778
10,058
25,435
Heattreated
42,109
25,548
12,721
31,032
33,662
W l d boar (head)"
600,000
450,000
n.a.'
3,600
10,000
Exportofpigs(numbers)*
Piglets
Importofpork products(metric
tons)*
1
Imports from andexportstoall EUmemberstatesin 1999.Source:EL'ROSTATCOMEXTdatabase
b
Sources: Eibersand Dekkers(2000),Anonymous(1999),andAnonymous(1997)
c
Nodataavailable
*
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vri
—
Fig. 1
Pathway diagram containing allpathways that contribute totheprobability of CSFV
introduction in the European Union
Fig. 2
Schematic representation of model calculations for exogenous pathways
Steps 1 & 2
for region of origin A
H « f trwtad pork
Non*««truud
product!
y- PloMti
pork producM
- BrMflirtg pigi
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Fig.3
Scenario tree for the exogenous pathway 'import ofbatch ofpiglets'
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Fig. 4
Scenario tree for the endogenous pathway 'direct contact with wild boar'
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Fig. 5
Contribution of regions oforigin tothe probability ofCSFV introduction into the target
areas
Probability of CSFV introduction by exogenous
pathways per EPIDEMICineach region oforigin
Probability of CSFV introduction by exogenous
pathways per YEARfor each region of origin
Germany
I
Germany
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region of origin
region of origin
France
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region of origtn
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region of origin
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Fig. 6
Relative contribution ofeach exogenous pathway to the annual probability of CSFV
introduction into thetarget areas byexogenous pathways
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VA1R5-PL97-3566
'Development of prevention and control strategies'to address animal health and
related problems in densely populated livestock areas of the Community"
Final Report
Edited by R. Huirne 0 and H.-W Windhorst2'
l)
Wageningen University, Department of Social Sciences, Farm Management Group
IIollandseweg 1, NL-6706 KN Wageningen, The Netherlands
2)
University of Vechta, Institute for Spatial Analysis and Planning in Areas of
Intensive Agriculture (ISPA), Vechta, Germany
FAIR5-PL97-3566
'Developmentofprevention andcontrolstrategies toaddressanimalhealthand
related problems indensely populated livestockareasoftheCommunity"
FinalReport
Typeofcontract:
Shared-costresearch project
Totalcost:
1,285,200EURO
ECcontribution:
1,285,200EURO (100%)
Commencementdate:
01-04-1998
Duration:
3yearsand6months
Completiondate:
01-10-2001
ECcontact:
DGVIF.n.3
Mrs.Isabel Minguez-Tudela
Coordinator:
Prof.dr.RuudHuirne
WageningenUniversity
DepartmentofSocial Sciences
FarmManagement Group
Hollandseweg1
6706KNWageningen
TheNetherlands
Telephone+31317484065
Telefax:+31 317482745
E-mail:[email protected]