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SHORTREPORTOpenAccessDurabilityassociatedefficacyoflong-lastinginsecticidalnetsafterfiveyearsofhouseholduseEliningayaJKweka1,2,3*,YousifEHimeidan4,AnethMMahande1,BedaJMwang'onde1,ShandalaMsangi1,MichaelJMahande2,HumphreyDMazigo3andMrambaNyindo2AbstractBackground:Long-lastinginsecticidalnets(LLINs)havebeenstronglyadvocatedforusetopreventmalariainsub-SaharanAfricaandhavesignificantlyreducedhuman-vectorcontact.
PermaNet2.
0isamongthefiveLLINsbrandswhichhavebeengivenfullapprovalbytheWHOPesticideEvaluationScheme(WHOPES).
TheLLINsareexpectedtoprotectthemalariaendemiccommunities,butanumberoffactorswithinthecommunitycanaffecttheirdurabilityandefficacy.
Thisstudyevaluatedthedurability,efficacyandretentionofPermaNet2.
0afterfiveyearsofuseinaTanzaniancommunity.
Method:Twotothreeday-oldnonblood-fedfemalemosquitoesfromaninsectarysusceptiblecolony(An.
gambiaes.
s,thiscolonywasestablishedatTPRIfromKisumu,Kenyain1992)andwildmosquitopopulations(An.
arabiensisandCulexquinquefasciatus)wereusedinconebioassayteststoassesstheefficacyofmosquitonets.
Findings:Theknockdowneffectwasrecordedafterthreeminutesofexposure,andmortalitywasrecordedafter24hourspost-exposure.
MortalityofAn.
gambiaes.
sfrominsectarycolonywas100%whileAn.
arabiensisandCx.
quinquefasciatuswildpopulationshadreducedmortality.
Insecticidecontentofthenew(thebednetofthesamebrandbutneverusedbefore)andusedPermaNet2.
0wasdeterminedusingHighPerformanceLiquidChromatography(HPLC).
Conclusion:Theresultsofthisstudysuggestthat,inordertoachievemaximumprotectionagainstmalaria,publichealtheducationfocusingonbednetuseandmaintenanceshouldbeincorporatedintothemassdistributionofnetsincommunities.
FindingsMalariavector-humancontactreductionhasbeenshowntohaveasignificantimpactindecreasingmalariatransmissionanddiseaseprevalence[1-4].
However,theuseofmalariainterventiontoolsinAfricaisaffectedbycultureandthesocioeconomicstatusofmalariaende-miccommunitiesandthesehaveinfluencedbednetownershipandutilization[5,6].
Atpresent,malariaendemiccountriesinAfricaarereportingawidercover-ageofLLINswithsomecountriesreportingcoverageofmorethan60%[4,6,7].
ThewidecoverageisattributedbythewillingnessofAfricangovernmentanddonorstofundthescaleupofLLINsdistribution.
Investmenthasprimarilybeenforlonglastingtech-nologybednets,includingPermaNet2.
0whichhasbeenevaluatedindifferentsettinginmalariaendemicregionsglobally[7-11].
Today,WHOPEShasgivenafullapprovaltoPermaNet2.
0tobecategorizedaslonglastingnet.
ThePermaNet2.
0netsaremadewithpolyesterandcoatedwithdeltamethrin,whereastheOlysetnets,whichareimpregnatedwithpermethrin,aremadefrompolyethylene[12,13].
Theothergenera-tionsofLLITNs,theNetprotect(Icon-Life)areimpregnatedwithdeltamethrinandaremadefrompoly-ethylenefilaments,whiletheInterceptornetsarecoatedwithalphacypermethrinandaremadefrompolyesterfilaments[12,13].
Lastly,theDuranetmadefrompolyethylenefilamentsandarecoatedwithalpha-cypermethrin[13].
Manyothersarestillinthedevelop-mentalstages.
Currently,someofthegreatestchallengesfortheuseofLLINsindifferentmalariaendemic*Correspondence:pat.
kweka@gmail.
com1TropicalPesticidesResearchInstitute,DivisionofLivestockandHumanDiseasesVectorControl,MosquitoSection,P.
O.
Box3024,Arusha,TanzaniaFulllistofauthorinformationisavailableattheendofthearticleKwekaetal.
Parasites&Vectors2011,4:156http://www.
parasitesandvectors.
com/content/4/1/1562011Kwekaetal;licenseeBioMedCentralLtd.
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(http://creativecommons.
org/licenses/by/2.
0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
settings,particularlyinAfricaarenetdurability,reten-tionandefficacy.
InTanzania,PermaNet2.
0(Vester-gaardFrandsenCompany,Thailand)isamongthebrandsofLLINsdistributedinthecommunityanditsdurability,retentionandefficacystatushasnotyetbeenevaluatedatcommunitylevel.
Itsefficacywasreportedonlyimmediatelyafterdistribution[12].
Longtermdataonitsdurability,retentionandefficacyisrequiredforimprovingtheeffectivenessofLLINsatthefieldlevelandthiswasthemainobjectiveofthepresentstudy.
AtotalofsixtyPermaNet2.
0weredistributedinlowerMoshi,north-easternTanzaniatothehouseholdsin2005andevaluatedin2010.
Theactiveingredientmeasuredamongthesenetsatthetimeofdistributionwas55mg/m2ofresidualdeltamethrin[12].
Ofall(n=60)theLLITNs(PermaNet2.
0)distributedinthecom-munity,only7(11.
7%)werestillinuseduringthefiveyearsfollow-upperiod.
ThisresultindicatesaverypoorretentionofmosquitonetsinTanzaniancommunity,afindingthatisconsistentwithpreviousobservationsfromseveralcountriesinAfrica[14-16].
Thedurabilitywasdefinedbythenumberofholesinnetsusedbythecommunityforaperiodoffiveyears.
Thesevenretainednetswerefoundtohavealimitednumberofholesalongbedanglescontacts,meaningnonehadverygooddur-ability.
Consideringthestrengthofthehightechnologyusedtomakethefibersofthesenets[17],theseholescouldbeattributedtotheroughuseofthecommunityasitwerefoundtobeonthelowerareaofthenetindi-catingtoughmechanicaltearingofthebedsedges(Fig-ure1).
Itisknownthat,thepresenceofholesinlong-lastingnetsreducestheefficacyofprotectionagainstmosquitoes[18,19]despitehighcoverageindifferentpartsofmalariaendemicregions[20].
TheNewPermaNet2.
0inducedhighmortalityforinsectary-rearedsusceptiblemosquitoofAn.
gambiaes.
s(100%).
However,amongthespeciestested,awildpopulationofAn.
arabiensisshowedlowermortalityratesthanothers.
Thisislikelyduetothepyrethroidresistanceconferredbythe1014F-kdrmutationknowntobepredominantamongmosquitoespopulationinthisstudyarea[21,22].
Afteruseforaperiodoffiveyears,PermaNet2.
0inducedreducedmortalitiesincompari-sontothenewnet.
Thiswastrueforallstrainsofthethreemosquitospeciestested(Table1).
SimilarefficacyreductionshavebeenreportedforothertypesofLLINsafterthesameperiod[7,19].
Fiftycommunitymembers(100%)respondedtothequestionnairepertainingtothewashinganduseofthenets.
Theknockdownrateseffectvariedamongmosquitospeciesforboththetwotypesofnetsassayed(Table1)andinFigure2.
Mortalityobservedat24hourspost-exposurefordifferentpopulationsandstrainsshowedsimilartrendsofknockdowneffectsforbothnewandusedPermaNet2.
0(Figure3).
Regardlessofspecies,asignificantreductionwasobservedintheoverallmortal-itywhenPermaNet2.
0usedforfiveyearscomparedwiththenewnetofthesamebrandwhichwaskeptinstoresincethetimeofdistribution(Figure3).
TheactiveingredientfoundinPermaNet2.
0afteruseoffiveyearswasundetectablebyHPLCprocedurecomparedto55mgofactiveingredient/m2ofthenewbednetofthesamebrand(Table2).
Thiscouldbeattributedtouseofstrongdetergentsforwashingnetandthedirectsunraysfordryingthemforalongper-iod[7-9,17].
ThefirewoodsmokeanddustmayalsohavecontributedtothelossofinsecticidesinLLINs[7,8].
Generally,PermaNet2.
0hasthepotentialtoremainintactforalongperiodoftime;andyet,washingtechniquesandothersocioeconomicfactorswithinthefamilyorcommunitieswhousethemmayreducetheirintendedfiveyearsefficacyasperrecommendationbyWHOPES.
BioassaysproceduresOneachnet,fourWHOcontactbioassayconeswereattachedandatotalof10mosquitoeswereintroducedintoeachcone.
Twotothreedaysold,unfedfemaleofAn.
gambiaemosquitoeswereused[23].
Wildpopula-tionsofAn.
arabiensisandCx.
quinquefasciatuswerecollectedfromanareadescribedbyreducedsusceptibil-itytopyrethroidinsecticides[21,22].
Themosquitoeswereexposedoneachnetfor3minutesandthentrans-ferredtoholdingpapercupsandprovidedwith10%sugarsolutionsoakedinabsorbentcottonwool[23-25].
Figure1AsamplePermaNet2.
0collectedfromthecommunityhousesafter5yearsofuse.
AREDarrowpointstheholeswhichareduetomechanicalcontactswithbedangleswhileaBLUEarrowshowsamarkonthenetduetothefirewoodsmokeindoors.
Kwekaetal.
Parasites&Vectors2011,4:156http://www.
parasitesandvectors.
com/content/4/1/156Page2of5Knockdowneffectswererecordedimmediatelyafterthe3minutesandthereafterfor30and60minutespost-exposure.
Mortalitywasrecordedafter24hourspost-exposure.
Mosquitoeswereconsideredknockeddownordeadiftheycouldnotflyorcouldnotstanduprightoneitherthesideorthebottomofthepapercups[23].
Untreatedpolystyrenenetwasusedasanegativecon-trolforeachbioassaystest.
Temperaturesof25°C±2andrelativehumidityof80%±10wererecordedduringtimeofthetestsusingdigitalthermometer.
Themeanpercentageknockdown(KD)at3minutesandmortalityat24hourspost-exposurewereestimatedforeachoftheevaluatedbednet.
Onewayanalysisofvariance(ANOVA)withTurkeys-KramerHSDwasusedtocomparethemortalitiesandKDsofmosquitospeciesamongthemosquitonets.
Allcontrolmortalitieswerebelow5%.
ResidualinsecticidequantificationFourpiecesofnettingmaterialwerecutrandomlyfromeachnetandthenappropriatelylabeledwiththenameofthenet,keptinindividualenvelopswhichwereinsertedintoasinglelargerenvelopeandstoredinthedarkforsubsequentresidualinsecticidequantificationusinghighperformanceliquidchromatography(HPLC)[26,27].
Foreachtest,theHPLCwasperformedusingapieceof5*5cmfrommosquitonetwith0.
15%gradewaterfordeterminingdeltamethriniso-octanplus1,4dioxananddibutylphthalateasinternalstandard[27].
Table1Percentageknockdown(KD)andmortalityat24hourspost-exposureofwildpopulationsandlaboratorystrainofthethreemosquitospeciestestedPermanent2.
0An.
arabiensiswildpopulationCx.
quinquefasciatuswildpopulationAn.
gambiaes.
sinsectarypopulation%KD(95%CI)%Mortality(95%CI)%KD(95%CI)%Mortality(95%CI)%KD(95%CI)%Mortality(95%CI)Newnet66a(52.
9-79.
1)46ac(32.
2-59.
8)91a(83.
1-98.
9)81a(70.
1-91.
9)100a(100-100)100a(100-100)Oldnet160a(46.
4-73.
6)58bc(44.
3-71.
7)73bc(.
60.
7-85.
3)62b(48.
5-75.
4)100a(100-100)30b(21.
2-39.
8)Oldnet260a(46.
4-73.
6)49cd(35.
1-62.
7)62cde(48.
5-75.
4)58b(44.
3-71.
7)100a(100-100)47cd(32.
4-51.
3)Oldnet358a(44.
3-71.
7)71b(58.
4-83.
6)75df(62.
9-87)49b(35.
1-62.
9)100a(100-100)33b(19.
3-43.
7)Oldnet454a(.
40.
2-67.
8)49ade(35.
1-.
62.
9)38b(24.
5-51.
4)44b(30.
2-57.
8)100a(100-100)50ade(41.
3-58.
8)Oldnet587b(77.
7-96.
3)75bf(.
62.
9-87.
0)60bef(56.
4-73.
6)54b(40.
2-67.
8)100a(100-100)33b(19.
7-45.
2)Oldnet654a(40.
2-67.
8)83bf(72.
6-93.
4)66ef(52.
9-79.
1)56b(42.
2-69.
8)100a(100-100)33a(23.
1-39.
4)Oldnet760a(46.
4-73.
6)73ef(60.
7-85.
3)49be(35.
1-62.
9)44b(30.
2-57.
8100a(100-100)53be(41.
8-61.
9)*Numberinthesamerowsharingthesamesuperscriptletterhavenosignificantdifferencesfromeachother(P>0.
05)0255075100DF=2,F=4.
52,P=0.
0290255075100An.
gambiaes.
sAn.
arabiensisCx.
quinquefasciastusDF=2,F=2.
71,P=0.
094PercentagemortalityABFigure2KnockdownrateoflaboratoryunfedfemalesmosquitoesofdifferentmosquitoesspeciesAn.
gambiaes.
sAn.
arabiensisandCulexquinquefasciatusagainst(A)Newand(B)fiveyearsusedPermaNet2.
0athouseholdlevelinLowerMoshi,north-easternTanzania.
0255075100NewNetOldNetsPercentagemortalityDF=1,F=267.
7p<0.
001Figure3Mortalityat24hourspost-exposureofunfedfemaleofAnophelesgambiaes.
s,An.
arabiensis,CulexquinquefasciatusagainstNewandfiveyearsusedPermaNet2.
0athouseholdlevelinLowerMoshi,north-easternTanzania.
Kwekaetal.
Parasites&Vectors2011,4:156http://www.
parasitesandvectors.
com/content/4/1/156Page3of5Extractedsampleswerethoroughlyshakenforuniformmixtureandfilteredthrougha0.
45μmmembranefiltersuctionpump.
Thefilteredsolutionwasaliquotedinto1μLandtheninjectedontoanormalphaseisocraticHPLCmachine.
TheinsecticidequantificationwasachievedusinganinternalcalibrationcurvebasedonUVdetection.
ConclusionTheresultsofthisstudysuggestthat,inordertoachievemaximumprotectionagainstmalaria,publichealthedu-cationfocusingonbednetuseandmaintenanceshouldbeincorporatedintothemassdistributionofnetsincommunities.
Thismaybeeffectiveforimprovingdur-ability,washing,dryingandretentionofLLINs.
AcknowledgementsTheassistanceoftheTropicalPesticidesResearchInstitutestaffinexecutingthisstudyisappreciated.
Wearethankfultothecooperationofthecommunitymembers,householdsandvillageleadersandtheirwillingnesstoparticipateinthisstudy.
ChachaNdege,PatrickTunguandJovinKitauareacknowledgedfortheircommentsontheearlierversionofthismanuscript.
VestergaardFrandsen(EA)providedthenetsandfinancedthestudy.
Authordetails1TropicalPesticidesResearchInstitute,DivisionofLivestockandHumanDiseasesVectorControl,MosquitoSection,P.
O.
Box3024,Arusha,Tanzania.
2KilimanjaroChristianMedicalCollege,TumainiUniversity,P.
O.
Box2224,MoshiTanzania.
3DepartmentofMedicalParasitologyandEntomology,Weill-BugandoUniversityCollegeofHealthSciences,P.
O.
Box1464,Mwanza,Tanzania.
4EntomologyUnit,FacultyofAgricultureandNaturalResources,UniversityofKassala,P.
O.
Box71,NewHalfa,Sudan.
Authors'contributionsEJKconceivedthestudy,designedandcoordinatedthestudy,performeddataanalysisanddraftthemanuscript.
SMandBJMparticipatedinthefieldworkandcarriedoutthebioassays.
MJMandHDMinvolvedinstatisticalanalysis.
YEHdraftedandreviewedthemanuscript.
MNreviewedthemanuscript.
AMMparticipatedincoordinatingbioassaysanddraftedpartofthemanuscript.
Allauthorsreadandapprovedthefinalversionofthemanuscript.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
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:Durabilityassociatedefficacyoflong-lastinginsecticidalnetsafterfiveyearsofhouseholduse.
Parasites&Vectors20114:156.
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