Reminder notes on the importance of hydrological data in the activities of the onchocerciasis control programme

WORLD H;:'ALlg ORG',}i'IZ." TION 0RG,'TNISATIOI{ MO}IDfALE DE LA SANlts OI,ICT{OCERCf/ISIS CONTPOL PROGBAI'0'IE IN I{EST AFRICA PRocnAiOiIE DE LUTTE CONI'RE L'OIICEOCERCoSE EN /TFRIQUE DE L'OIIESIII I'IATIO}IAI ONCiIOCERCIASIS CO|']{INIEES Tenttr meeting Cotonou. 1-5 June 1:)85 NOq[o.6 ORIGII.IAL : ENGLISE REI\IINDER NO 'ES ON II{E IMIICRT/ NCE OF iITDROIOGICAL MEA I}I $TE ACTII,:IIITES OF THE ONCHOCERCIASIS @}ITROL PROGNAMME 1. The onchocercia.sis contml strategy is, at nree€Dtr ba.sed on tle Brinclplc of repeated applications of chemlcal insecticides against ttre lazrra of the blaclcfly ..r"ito". tte"e larwae which are bottr a.puatlc and rtreophiloue, Il.ve, attaotred to sub- merged substra'tes, in low depthe in the current of the wata:rcorrBeBr Ilney feed paa- sivIly by filtering wrter from the rivers thanks to a special ;natoml.o devLce $btctr t],ey ion-sess, Tfrif feeding hatit ls taken into accor:.nt in ttre ftght agafnat Simrltu d.amnosr.ig s,lr ! the cornplex of rtv^r blindness vector specLes 11 West AfrLca. [!re a^.u.*ic sta5;.;s of these vectore, whose larnae feed., without distlnctlon, on substanceg broueht by the cur^rent, are desiroyed when an applopriate larvicide ls sparyed at the .idet concentration into ttle v'' tercourses. n. Though si.nnnle in principle, the spraying of a pesticlde in an aquatic envlroment presents en orerationally compl.6x e.sroctr fhis complexity is related to tlr+-hydro- iogical , hyrira.ulic anrl biotic conditinns of the river€, The ooerational eoncentratlons .of ttre insecticides utilizedr .rhatever they may be, should be gelective. They mrst read to complete erimination of the blackfry larnae while prese:erring the aquetlc fauna ;nd ff.ora, Suctr nrecision can only be attainad lf the riner dlscharge, at the tine of the laryiciding, ls known wltJr an Llmoet uathematical exaetttuda so aB to celculate the doses to be spriyed. If the dosage is nqpppalab for the discharge lt has congeguence! detrirnental to the coet-effectiveness of the control operations, be lt an unden-dosage or an over-dosa.8p, ,. An un6.er-dosage is necessarlly a rislry act in all respects. In additlon to the risk of seeing the.Loeal developmeirt of a resLdual veetor loprllation (ttrerefole en uninteggipted tra.nsmlsslon) ttrere is that of an tteaslyt alrpearance of the rcLnnasLonpfrerro-rttr, Under-dosage ls certainly a uaste bactuse the obJective al'ncd et 1g not attained. Over-dosage is also a source of waste bece"use of the use of unnecesB?4r euantities of the product. tr\rrthermore, lt is har.rnf\rL for the envLronpent.-eBpecla1ly '^rhen inseeticides not tolerr.ted. by it a.r:e em'lo0red. It ts ttrerefore B?eBslng to have hyr).rolo.-1ca1 data roliable both ln tine and BPace, 4, H,:lfVay tlrrough the fi$nt ar:ninst onchocerciaeis in tl1e lnitial Prograuma area and on i,he eve of t].e iaunching of the carpe.ign in the extension areasr Lt has becorp neces- se,ry to r.eview the hydrometric network si.tuation ln ttre OCP area for the attention of the Particin:ting Countries. fhree mal-n reasons underLle that ; a) Ivlany st^tions rmrst be re-calibratod beca.use they have deteriorated in dlfferent ways over the years ; b) wigr the ex:rected appearance of -esistanc€r OCF contirmes to modlfY Lte control It*t""y and t.ctics ln order to nreserrre tJle gains. r!:ie modificatLon makes lt some- timeB xse srir-eeessivoly during one and the ea.me Beason severnal ineeotLcld,ea for the .../... NOC10.5 -2- trtatment of one and the sa.me rratercour?sa, c , A hidr technolop-y has been brought into nIay, f t ls that of teletransmisr{on of thp hyd.rometric data. This technolo6gr could bo ttre ideal ttring for OCP actlvltles be- c'tse of the problems o'a.ceessibility and sometimes too long delays b.tvreen tJlO ttne of 1:t-c1'eid:.ng and th,t of the ree.ding of ihe vrater levels by tJre monitoring teanoo 5) The'r:aliW of the hy<lrt'rmntric netvork varies from country to countzy. In toroe of ttrs colrr. lries, in lhe ma.jori ty. 1.hi:r nnt'work is conl,inurrlf, malnta.lned and the datl undatcd eifther by thc n tional t.ams or the specia.llzed 'ubcont,ractor teams or throtrgh. tlre com- bihed effort of both. Tn other c'rseSr the si1,u;r.t.ion ls of coneern, OCP has alffeady 6r[e necassary contaets for the repair of defective stations and ttre re-calLbz0tlon and esitablishment of nel, Teting eu::ves some of whictr are ten or fifteen and even 20 yearg ol[. If the work has not been started as yet, lt ls desirable for it to be co$nencod ln thF nea.r frrtrrre because of the above-mentioned reasons, A group of hydrolory 0.hd telG- trtnsrnission ex:rerts who met under OCP auspices in Kara last I'lay enphasized thi urgency of' the situi.tion and'letermined the minirmrrn needs to be met. tr\rrtJleurore, Lt fEcoumen- aeE tlre creation of OCP'S own hvdrologist teams atta.ched to ttre aerlal opelatl0hs baget lriith a vi".w to inte:rre''ing as and when necessar]r in the maintenance of the hydfbmetrlo netpork a.nd in the use of th' da.ta it provides, 5) The role of hyfl361ogy in OCP activities whictr vIaB nacessarily lmportant trF[rc past r*i[-t stil]. be,-reater in the f'rhrr.e in view of the second-f,nneratlon Lneectlcidps vhldt OCF tra.s,Eot in order to ov.rcome the r:eslstrnce phenomenon. [he aquatic envlrQhmcnt hats satisfrctorily tolerated tho first-,"cnera.tion insecticides whictr lnclude t0Eephos(used. for more than a d.cade), chlorphoxim and Bgcillus thurlnSlensls sero qrpF E-14(U,l n-f+). Annong those of the second generation, the pyr'ethroldB (permetrin) hnd calbamates (c' rbosrrlfanl should be m:ntioned. 7) The lncrease irr the irsectj.eide arsenal calls for a more precise larovrledge of the dilscharge of tho rivers to be treated, especially at the very time of t}e larvl.cidtng. Thie regrlar urdrting of the hyrlrometric n^truork and the adoption of an uLtra-flEd ne,ans o{'urrngrnlssion of the h.,r.lrolonical datA ar"e conseruently a vital necessity fof the d4ily activities of th. Pro,Trarnme,