The reinvasion of the Onchocerciasis Control Programme in the Volta River Basin by simulium damnosum S. L. and possible benefits of extensions of the programme and of control programmes in the Senegal basin and Nigeria

OT trHE iircæn coNrRoL drr,rrt{oRg, zz IVORI(ING GROUP - 25 Septenber 19Bo a" MÊNIHG PÂPER I ,} THE REINVASION VOLT RIVER BASIN EXTENSIONS OF THE BERNEÂRD-NO CET- INS T ITUT OF lHE ONCHOCERCIASIS CONTROL PROGRAMME IN THE BY STMIILIT'M DAMNOSÜM S.L. ÀJ{D POSSIBTE BENETITS OF PROGRA}4ME AND OI' CONTROL PROGRA}II{ES IN TIIE SENEGAL BASIN AND NTGERIA BY R. GARI,TS riin scRrrFs- IIND TRopENKRÂI{KEErIEN, EAMBITRc Fia. I 'al:rp § r+C i grt * ** ll*ur,tS ;., Oougouni. t.. t.. . ). . .. lJ|: oa -ilt:;T;iili:; lr{ tar QtP' ",' !n ot phaee I and Phase IIT lllestr every-day catching g"""oo"-..upecies S. daranosulr s. stl.,/S. sl.rbanum (frora Garmsrlïalsh & Davies 11979) (p\ ,.ta.(a\o\ .o\ \ \ \\{ 9\=É \iO rool \ '\:'. .o. \lt)i1i ! 0, o o ! Â, at o . Banrora E lortôlx 1t II o È BOUAK E a ABIDJAN O@eru ry-day catching stations ^-O-Breeding sites ol S.damnosum s.str./ S.sirbanum BoundarY of OCPL-_ sp IOO km .::::!i!i:.ereas o,f reinvasion ......- -t- I rrirno»ucrroll The phenomenon of the reinvasj-on was first observed in the rainy §eason of 1ÿlJ. Shortly after the aeria-I operations had started in February 1975 t].y densities rapiùLy declined ia the entire Phase f area. Eosever ia Aprilr at the end of the dry season, lncreasing numbers of §i+u1iun damnosun s.L. females reappeared. Ln sottrê parts of the progragme p.d were particularJ.y observed al.ong the rivers Banda.uoa, Bou, Lôraba a3d, ' Konoê i.n the south-west and ühe Black Vo1ta aad the Bougouriba in tb ceatre (mg 1). Intensive surveys were carried out irnmed.iately but ôid. not reve,l failures of treatmeat or breeùiag sites wtui.ch had not beea found before, which could expJ-ain the high aunbers of biting f1ies. ft had to be concluded that the 'f1ies did not orig'inatc from the area ltseLf but were invaders from sources outside the progr4.rnne. This reinva,sion continued throughout the raiay seasoD and bi.ti-ng densities did, not decrease to Low'numbers before the end. of §eptember, though occasLonal outbrealcs were observed even later in October and. November. Such a reinvasion- occurred agaiu during the rainy seasons of the folLowing years and proved to be anr annua'l occurrenceo Whenr tn 1977t the progranme area was extended into north-western Ivory Coast and further westward into Ma]-i (phase III West) tUe reinvasiou iuto Phase I still continued endr furthermore, tt beca.me obvious that also areas along the Bagoê, Kaakelaba, Baoulê and. Ouassoulou rivers rere being reinvaded. (trlg.1). À sirn5.J.ar phenomeaon occured ia the SE in Togo and Benin wh.ere the control operations had started in the second ha-Lf of 1977. Th.e actual zonc affected by thc reinvasion was less than Jo % of tlae total origina-l program€ âr€âo Eowever flies probabJ-y penetrated to al-I parts of the programme area buü generall-y in numbers which rvere epid.emio= J.ogically insignlficalt ( OCp Evaluation Report, part I, 19?8). Their presence could be inferred onJ.y when ühey happened to colonise an turtreat= ed breed.ing site where a smalL population then developed to a detectable Level. The SinuLiidae have long been noted for their diepersivc ability and -4- windsupported displacements have been described on many occasionso Also S.damnosun s.L. has been suspected of travel3-ing distances of up to 1Jo kn with favourabLe air curreuts especially those occuming rith the shift of ühe IntertropicaL Convergence Zone ( tTlCZ ) fron the coast 'towards the interior at the beg,inning of the wet season. such long ùistance f15.ghts wouLd ensure the aunua-l repopulation of S.dannnosumrs temporary Iarval breeding sites ln the d.ry savanna, when the water= courses begin to flow again ( WXO, pAG report, 19?7). Eaving this ln uintt the bouadaries of the OCP çere set so that a large central area worrld be protected.. Eowevcr, the events of the rainy seasons of 19?5 and of the foLlowing years c].ear].y demonstrated. that the area affected by the reinvasion'was J-arger thal had been aaticipated. and the epid'emiological inpact by the high numbers of f].ies was uore serious tbaa had' been "*p"àted,. Furtbernore J.t was fouacl, that a high proportion of the flies caught ln the rcinvaded areas was. infective. Presumably these infections lf,ere a-lready. picked up before the ff-ies had entered the pro= 5râ"e arear suggestS.ng that the OCP was being reinvaded not only by the vector but also by the diseasct6 organisn. The rej.nvasion of the Worlct Eea-lth Organ:ization Onchocerciasis Control Progra"rrne area by S.da.nnosr:n s.1. feaales orig:inating fron sources out= side the prograrme Értea had to bc recogulzed aE one of the most serious problems for the whoLe scheme. Every effort had to be nade to explain the pheuomerotlr to detect and cootrol the areas of departure of the J.nvadiag fLies. The reinvasion was studj.ed i-n detaiL fron 1g?5 lo 19?9 tn the western and southwestern areaa of the prograrune where the probJ-em had beea first observed ( Garros ct a_L.19?9t Wa].sh et aI. in prep.) and, Ln 19?9 aad 1ÿ8o, in the cast in Togo and Bcnin. Methods used for thesc stud,ies were described by Garms et a_1. (19?9)" THE REINVASION OF THE WESTERN AND SOUT}II'IESTERN AREAS OF TEE OCP Garms et al. (1979) and Walsb et aI. (in prep.) gave a detailed account of the studies carried ouü in these areas between 1g?5 and 1929. The naia conclusions were as foLLows i The reinvasi.oa of the progranme area by fenales of S.d.annosum s.L. is an annual occurrence associaüed rrith the ret sea6otr. Maia components of the reinvading f1y §.§ry s.str. and onset and. d.uring the Tbis movement ensures breeding sites aLong E -)' ;., populations are the two savarna cytospecies Sosirbanum which nake an a-nnua-l nigration at rainy seasoa from the perennial- rivers of the south. the repopulation of the tenporary wet season the savanua rivers in west Africa. the The studies indicated thal this movement is across country, probably in a SW-NE directi.on over Ivory Coast, Upper Vo}ta and part of Malit end is associated rith the northward, movemeat of the ItCZ a^nd the monsoon rinds which foLlow it. The occupence of invading fliea appeals to be most noticeablc up to èLstances of Joo krn fron the presumed aourcest but occasional sroalI concentrations of flies nay aPpear uP to 5oo km awayt aad it is possibLe that a few raay be carried. further ( l'ig. 1). Invading flies appear to be older parous fenales lnany of which carry infectlve Jrd stage larvae indistinguishable from Onchocerca Iglgsg' It is thoughü that the novement talces i:lace after a blood-mea.} and may be stinulated by t,he need to fincl an oviposition sitc. The concentration of invading flies rhich appeat aLong certain rivers represent foci for the traasnr:lssion of onchocerciasis. Fo:ltu:rately these fLles tend to remai-n close to the river vegetation and thus the areas of maa/fi-v contact is limited to the river bank and aot rideLy dispersed as with pre-control- breeding populatj-ons. The forest cytospecies §.sanctipaul-ir S.soubrense and §.Ig§E rareS'y occurred at catchiag eites deep inside the progrâJrnê ârêâo Increased numbers of forest fLies were onl-y caught wj.thin 5o km of the programme boundary. This was in spite of the fact that breeding sttes of these species were nunerous in adjacenü fl.ight behaviour of ühese sPecies and S.sirbarum. area6. Tb:Ls strongS-y euggests that the êiffers from that of S.d'a$nosu.6 s.stro Owingtod'ifficu1tiesofdistinguishin8g"ry(inpart)from S. damnosum s.str./§.gi"b* it was not possible to state how i-mportart this species was. Bowever, results of eLecürophoretic id,eatifi=a migrant cations nay be smaller carriedoutbyTovmson(gzg)suggestedtbataIthough§.ry found, a!1ong invad.ing f1y populations its dLsperbal is on a nuch scale than that of s.damnosun 6.8tr. anrd s.sirbanun. -.-L*È -*ÿfi " ,: t' i rlti1J!ï Itl, : Il,tl, i O 7ztzt}., l-r. F.FGIo if o'xpETNopTE..P.oEtst,o Èp§o14 <+ÉPF,G<HOÉd <rljT ^(+o,*p Ed5cr !, Gl§5o 9,È5ÊroÉE troFtl l-oBctHrlJl* <octo O ;ÿts,o- È(+ u, 0,p,rts F ctOrÈo TnroHr:iYpp .O l+, (ÿ P t:CPT l-r. o,p0c@ it. Oor Or P.H§5orUF,ÈJ0'\Od anN pÊ, o\0). ),o}J.p r<5\ooÈ{ r,,T:l-p poÿF lÀ!, ÈôooP.JF\Oro{ . CoO|t o ordE l'Àf'd 0g0r. iF'J I È !,{5P.È(tÈÿc) Eq,oÉ>ro H. ùrOorÈo o :,2 tg Jô-=lo r: ô{zc--o i;: at' !=1 âi;:é.- c-c-; .(o { ,l i 1I s i i Ft T o!l c)p r.t o-â <.- '€' ., ut R9 Up l* o Itt \o{\o _.-.- --- i I I i SOUfiCES OT THE -7- REINVASION OT TIIE WESTERN AND SOUIHI'IESIERN AREAS tji I 1,he areas of departure of the fLy popuS-atj-ons reinvading the western I regâons of the OCP had to be sought in areas were breeding sites of S.deqnosum s.str./S.sirbanum were highJ.y productive at the end of the dry aad during the wet season. Detailed surveys camj.ed out between 19?6 ar.d 1978 revealed that both savanna cytospecies were far more wide3-y di6= tributed south of the progranme area ( Eig.1) than had been thought when tbe boundaries of the prograrnme had been set. Thc nearest potential source for the rej-nvasion at the Léraba river was the upper Marahouê river S!11 of ühe ptogranme boundary, involvj.ag a novettrent of about 25o kn for nigrating f1tes. Eowever, siace in 1978 the upper course of the river ras sti1I dry when the reinvasion began, dlsplacements of large nu-mbers of flies over distances of Joo km, or even morer had to be envisaged ( Sassaadra River - Leraba Rlver Joo km, Sassandra River - Bougouriba IùLver Joo km ). ExperiuentaL treatments of river eystems soutb and, south-west of_ the prograJlne area, which rvere suÊpected to be sources of the reinvasion, were carried out for firnitsd periods l.n an attempt to identify the breeding sites of the nigrating f3.ies and to i-mprove the situation Ln the invaded. areas. Such treatments, so far, proved to be the best meaJs to rliscriruinate Elources of reinvasion. ResuLts of such treatments of the Banciama rlver b, 19?6 a.ud the Marahouê, Banaroni and Sassandra rivers 5-n 1977 aad 1978 are described by Garns et aI. (1979). Soon after the comrnencement of experimental treatments of the upper Mara"houê, the Banaroni and tbe §assandra and, its tributaries in June/Juay 19?7 fJy clensities d,ecreased to low leve1s aü the Banda.na, Bou and. Lôraba rlvers, and, no further peaks of reinvaslon Eere observed untll the end of the rainy seasodtr g,2).This result suggested thatfor the first time, nain sources of ühe reinvasion had been controlled. In order to confirm these resuLte thc Sassandra and Marahouê river basias were treated, agaS:r Ln 19?8 a6 soon as they started to f1ow. For the first tiroc biting denslties et the Lêraba river remained at a relatively Iow lcvel throughout the sêâsono Pronounced pealcs did not occur and biting densities onJ.y trice cxceeded 1oo fLLes per day Flg.2).Oa the Bougoq rj.ver fli.es were extrenely rare in comparison rith previous years. Oâtlîu Bandana ald the Bou rivers a considerabLe reinvasiou was observed during the seco.nd haLf of ÀpriJ. and in early May. After treatmeats of the :j -8- J §lsoandra basin bitlng densities decreased, on these rivers and, on the I ,rip"r Bagoê. Eorzever, ühe experimental treatments did not inprove the sltuatJ.oa j.n the rest of Phase fII West wh:ich certainly was reiavaded fron other soülcêsr TEE ETFECT OF THE EXTBISION IN IVORY COAST (PrASg ff) ON THE REr}ruAsroN . The experlmental treatmeats of the Sassandra basin and. the upper Marahouê system which were carried out in 19?? aad,1928 dial not yet lnclude a-11 S.damnosum s.str./S.§irbanum breeding sites in the S.ancl. SW - of, the OcP. Therefore, when in Decenber 1 9?? i-lne Joint co-ordinating Conmltteer the governing body of the progranme, approved a request by the Ivory Governrnent for an extension of Sinrrtiun control operations south= wards the exact southern Lilults of the progrartrme area in fvory Coast were set to lnclude all areas rhere S.dannosuru s.stt./g.sirbanum were known to breed ald. which rrere potential sources of the reinvading fli-es (f1g.31. these vector coatrol operations commenced, at the beg:innlng of March 19?9. the results of these treatnents wil]. be given in detail by Wa1sh et aI. (in prep.). Às shown by Fig.4 BrC biting densities at the Upper Bandama and the upper Marahouê d,ecreased to extremeJ.y low J.eve1s rithout cpidemiologtcaJ- significanss. Very IJ.tüIe movement of flies was recorded lnto the Konoê area and alnost none occurred in the Upper Black Volta ald the Bougouriba. Àt the teraba r:Lver ( tr'ig.4.4, ) whiLst there was und.oubteùLy a regular lafrux of flies Ln 19?8 ühis was at a Lever very much Lower than in previous Jrears, but in 1979 it had ceased to be of epideroiolog:lca1 slgnificâD,cêo llnfortunately, in 198or biting d.ensities were hlgher againr although never reaching the 1eveJ.s of previous Jrears (tr'ig.51. Thus it'is now certaia that the Upper Bandama and the Leraba val,Ieys tere being reinvaded by 3.arge numbers of fJ-ies from the Marahou6 and Sassaldra basins rhere S.d.annosun 6.str. and, S.sirbanum were known to breedo Movements of at Least ]oo kn by large numbers of flies of these cytospecies are confirned . Ilowever, the continued i-nfLux of fl-ies of S.-damnosun s.str./S.sirbanun , and even the occurrence of notj-ceablc pealcs 1978/19?9, areas rhich were stil1 and river sect,i.ons first treated i:Flg. 3 : reinvaded 1979. iooooolro Extension la 19?9at"l l attt tl .BAul*i; a ttlat an, , ;l;6l,u. olo -,-- I I \ \ \ .\gÉ\i ?'t i \ à\ lio' \)r\t \ \ \ \ \ \ \ /II o\qrl B\ Phase lV ,t9) .Ùt.' c(!i Y' \ Tt.t \u r1 :: : :r .o à 0 \ol=lo fc3r..' tt, trI * o t l1 o \ E o! o x r<.lo); l? I , at( a aa , a P-'§, (tr \ ,II ,t a a a a a a a a BOUAK E a o\ t\ I , , t ,lr I , ,t , ni tI , \to oMa ,tI\ x o a ----_§I!ej:t_on ABIDJAN o ^æ first treatnents ln 19?9 areaa of reinvasion Ln 19?9o 50 100km - 1o - Flg. lr and, Fig. 5: Daily biti.ng rates at leraba bridge (Lêraba R.rsite of I'ig.1)r Ch.Niakaramandougou (Bandama R.rsite 7) and Station Mermis(Marahouê R., site 2J) Ln 1)18, 19?9 and 198o. Fi.g. l+ A .;\.': i, /t . ,r'i; i i :' , -j'. : iitji'lj',i;j i !'': :r '.--jji:r' i.j i i , !: :t :rI r'-; .! ilL. I . ir'r ..i !l ï ,'i:',1 l'.iiiii iI i,'l \i' \j '\: I ilti ÀiJiiv iltfliiit\i ! q c I [19'5 :I?atlo 1 : lpftt to r+ i CaÈching sltc : Bitlng .Iunc 198o River Map siteFig. 1 - 11 rates and tra.asmission potentials for the periodat some catchi-ng sites in the western areaÀ of ocp (, _ 3- ,.) (n^ i.--«, Biting rate Trrnsmission potential ,1 L6raba bridge Ch.lliake Gito ] ' l,Ieruls ' Kato Pt.SeguêIa Bac Seniêu Massadougou Madiaa Diassa Pt. Ta,nfoJ-i1a KankeLa N'Gapyê Kouoro Laayiera DJ.ebougou Léraba Baad.ana Bou Marahouê Bauoroni Banoroni §assandra Siên Baou].ê Ouassoulou Kankelaba Bagoê Baniflng B1ack VoLta Bougouri.ba 1 7 9 ?3 25 26 28 27 2o 22 18 17 16 1o '13 888 48 t64 78? 15oj 5o8 9't ,44, 155o6 J4o2 6769 1o6 99 3o 2 . ^.."b 6.l- a L.aL , o -,s 1L- '/ 6t 4 t1 16 ,4 o o 191 84t 168 686 16 o o o ,i 14 Blting rates andby WaLsh et a1. transrnission(tgz8) potentia-ls rere caJ-cul_ated as described \tI I , II ,t I B rrrj o l-r rtQO.§ .i oi l'r.F..P OTooEÊIllo oo{olÿPl&o§ÿ o{Éo l.r. },lo oPB -O .P.p5§<ÈÊrÈcr(o ïP o o14È5l4 lJ Q\Oæ o : o FÀ(t o o o)t lrâ alo IEl5lolo IE o oÊ T lur ràIl*ITldlpl5 IE lÀ T 6) E u. Èt o F Fï oÈtol Iol 'rlT:olt*lttl DIoll}IolEI ol ks§FO l.r.{tI (tdTrJooooÈÈFP.!,5Èe r, o l-r l.& <rtO(DT oo ooËrt lÿrlur lÈlÈ lB l§ IB IElo lolÉlÉ lE l5 r-.P $/. crt, .l- àroQlosllâ Fl>, 5lcr olptrl5 IE \ \\ -..-/ z-\..-Ye^ ?o l"/ilo Sÿkarani 6)C 2 rn Sassandra -1uS ,/§'>V =o7 C)o a \I I l l--Q3ro §5 * o th o I1 \ 'tV\\ ttI 1- - §" -1r- of biting flies at the L6raba rlver siiuated 4oo kn from the nearest rnajor uncontrolled, breeding sites of these cytospecies is strong evid,ence for qui.te substantial novements over even greater distances. The facÈ that the extension of controL into the Marahoué a'rd. Sassaad.ra basj.ns eliminated the major part of the reiavasion in the üpper Bandama and Lêraba areas but had Little or Eo effect on most of pbase III West also confirras previous findings ( Garns et a1. 1g?g) coacerning the direction of fLies rbich ln tbis area must be predomiaaatly from Sril to NE. However, the flies involved ia tbe resid,ual invasion of the Lêraba area nusü have come froa other d,irections a6 no substantial nntreated breeding sites of s.da:anosum s.str./s.eirbanum renain to the sw. îhe present situation of the reinvasioa in the western areas of.the OCP is shorn by F1g.6 and Table 1 . In 198o ( eprif to June) there raa a heavy reinvasion in the reinvaded areas ia MaLi otr the OuassouLou(Yanfolila), Baoulê (Madiaa-Diassa) and KankeLaba rivers (Kanlcela brid.ge), substantial reinvasions oa the Upper Sassand.ra (Massaclougou), upper Baaoroai (rato) r upper Marahoue (Meruls) and, Lerba rivers ( L,6raba bridge) Reinvaslon activ:ities oa the Bou, upper Banrdama, Konoê, Bougouriba aad, Black volta rl-vers were ÿery J.ow though stilL noticeable. the nearest known breeding sites of savanna cytospecies are situated. rest of the OCP ln the Republic of Gui-nea aad have to be consid.ered as the potential sourcêso STMULIU},I DAMNOSI'I,I S.L, IN GUINEA The dlstribuüion of S.dannosum s.1. ln Guinea was studi.ed by Garms and Post (1966). As shown by Fig. / S.Èamnosum e.1. is wldely dis= tributed in Guinea. All J.arger rivers of the country are iafested, at least ia part, ald probabJ.y the ?rea of &istributioa covers the wholo country, Breeding sites were particn1arly forurd over long stretches of the rivers in Upper Guinea, a reg'ion which is d.rained by the Niger river and its tributaries ( sankarani rrith Goue'r ar KourrirDjoa, the Mi1o, Niandan, Mafou, Tinkisso). $Ihi1e the 1ower couraes of these rivers ia Guinea are raore or leos free of larger breed.ing sltes there is probabJ.y a continous breeding in their upper coursea ( trtg.6 ). Less infornations are availablc for oüher areas of Guiaea, ae for the Fouta DjalLon and thc western reg'ions of the country but find.ings suggebt that nost rivers are heavilv infested. -14- ( I rÊ c/_\7e D' JVOIp E ./o\ o.lo O ! rofo 3 \o\o o\ -{,Io sE oü o Etrdo o! r9= i.g5is t .cr I s î;!.i.:zlqbCîü-a--p!!è oùo= C.{ ! OF{ aÉ6 orl E:l +t ,l qlt olo € olE!t\T{ ÉlT{ :f. EL 'ati €lo . dr{ o (h ê s2lï{ )§7 o /o-ai§ o r! &#\;- _15_ Records on the distribution and ecologT of the different cytospecies of, the complex were given by Garms and, Vajine (t975). As shown by Fig. 6 §.dannosum s.6t!. "n,1 §.g{!g43g were wideJ-y distributedparticularly in the savanna rivers of Upper Guinea but, in the south, S"damnosum s.str. i.s penetrating even into the forest regj-ons of Liberia. The map is based oa cytotaxononic identifications wbich were carried out by Dr.Vaji-ue ( Garns and VajJ.ne 1975) a-nd on norphological identificatj-ons of adult flies which were emerged from pupae ( Garns, unpublished). S.sanctipaulirthe nain species of I-arger rivers in the forest region of West Africa, was ldentifi.ed only fron collections made in the Makona river which forms the boundary betweea Guinea amd L5-beria. But §.soubrense was found i.n the Nlger and. its southera tributaries. S.yahense generally kaorn to'be a forest species inhabiting snalJ-er shaded streams was found ia the forested areas in southern Guiaea, but aJ.so in the Fouta DjalJ,on mounta,ia6. §.squanosun was not identified from the materia]. collected by Garas and Post (1966) but the. preseace of this cytospecies was confirmed by Vajime ( persrconrro) who studied nateria-l sen't tô hin Later by the "qÏ.p" nationa-le de Guiaêe. POSSIBLE BHIIEFTTS Otr' CONTROT OPERATIONS TN GUINEA I'OR lHE OCP The nost likely sources for the continuing reinvasion in parts of the westera reglons of the OCP are the headwaters of the Niger and its southera tributaries ( fig" 5) shere savzutna epecles of the S.damaosum conpLex are known to breed,. These breeding sites are located. 2oo to Joo kn southwest of reinvaded, areas in Ma-li ( ouassoulou, Baoulê, Bagoê, Kankelaba Rlvers) antt about 4oo kn of Lêraba bridge. This ls in agreement sith the èLrection of the prevai1ing winds during the wet season aad rell rithin the pres 'rned flight ratrge of nigrating populations. It can be expected that control measures in Upper Guinea which should include the wholc Niger basin end possibly the head.waters of the seaegal- basin (Bafing, Bakoy) would, be of extreme benefit for the western areas of the OCP. Breed.iug sites of savaana species are widely distributed a.Iso further west in the Garublé, Coli'ba, Cogon, Konkourê aad Mono basins. Althougb tluis seems to be Less Like1y lt caanot be excluded that also fU.es fron these areas may reach the OCp. -16- . TURTHER SOURCES Or RETNVASTOIüS Or WESTERN ÀREAS Or THE OCP The assumptioa that areas ia Ma].i are being reiavad,ed from sources located in the Niger basin in Guinea does not explaia the occurrence of fLies in some parts of Ivory Coast e,g. al.oag the headwaters of the Sassandra a''d at the Banoroni (I'ig.31. The species composition of these fly populationÀ should be studied in detail since S.S;qqgrmosum night be involved origiriating frotn breed.ing sites in the mountaiaous regions around Man which, for techaical regions, rere. aot tncJ.uded. to phase IV. Further potential sources are the upper courses of sone tributarj.es of the Sasso"dra ( Boa, Feredougouba) wbj.ch flor tbrougb Guinea and, could aot be treated. Furthernore it shoulcl uot be forgotten that S.damnosum si.str. was a].so fouad, in sorae .rivers in Ltberia ( st.John, cestosJFige§l"a 25o kar SW of the reiuvaded areas on the Sassand.ra. But nothing is yet knovm about the prod,uctivity of these rivers. f13.8: ÂÎar! of t.{ôl.tlol Lr !o6p ud Benln trd potcnÈl.l sourccr ot _ tà. §.jl:Igg:g ..rt8.,/S.51!crnu ,qinvrgroa S ua Sà of Èh. OCp. HAUTE VOLTA GHANA \\ \ \ ri I I I I I I\ I I I\\\ -- brrcdlag rl,vcrs cl§. dæno6ui ..tlr.,/S. slrbânua I , tII I t I .1 Bt.qdlng clt.s r.! lllgêr1a rccordlig to Crorai<ry. 1ÿÿ BENIN )v, La3cs _.t7_ THE RETNVASION OF îHE EASTERN AREAS OT THE OCP That a reinvasion also occurred in the eastern part of the OCp where control measures comrnenced in the second, half of 1977 was su6= pected tluring the rainy season of 1978 when large numbers of f1.ies re= appeared along river systems in Togo and Benin ( lVatsL et a]-. 1929) " More detailed studies on these reinvaslons wore carried out in 1979 and, 1ÿBo by Garms eü a-l . ('tg?9r198o)" Areas partlcularly affected by a reinvasion were in logo the Mô and the Kara va11eys, J.n Togo the Sota and ühe AJ.ibori basin and possibly the Mêkrou river (Fig.8 ). The re-appearance of fLies within these areas was noü synchronized at the ôifferent catching sites, rhich contrasts with the typica-l patteru of eveuts associated rith reinvasj-ons in the western area6 ( Garns et a-L. 1979). This lack of synchrony was particularl apparent in Togo, where the sites beside the Mô river were invaded much earlier than those ou the Kara river ( I'ig" 9 ). In Beain the number of flies at the Sota, Àlibori and Mekrou rivers begaa to increase-at the sare time after the beg:inning of June, buü Later on very high nulbers rere recorded l.n Augusü oaly at the Sota aad the'Alibori rivers ( ris;9). Thus the differences ln patterns of f1y numbers appearing at d.ifferent sites suggests that tbese sltes were invad.ed from different sources. Iü was of special iaterest to note that a-lso the species composition of the invading f1y popuJ-ations were dlfferent from those observed ia the western areas of OCP and varied at different sites. While in Togo, especially along the Mô vaJ.J-ey, §.squanosu.El was by far the pred.oninant species, the proportion of §.§ry s.str./S.§irfu within the reinvading populations increased further to the east and the reinvasion in Benin was a'lmost exclusively by these two savaana epecles. SOURCES OT TIIE REINVASION OT THE EASTERN AREAS OT TEE OCP Sincerin Togo, §..Sarnog contributed to about 8o % of the invading flies aud to about 76 % of the traresmission potential ( Garns et aI. 198o) it was of specla-L inportanrce to detect the sources of these fLies. Breeding sites of this cytospecles are mainJ.y confined to the rivers in the south rithia and cLose to the mountainoua areas a-1ong the Gbana/Togo border ( r'ig.ro ). Apparentry breeding eites of §..rygggg "r" dâBstrtfrom Benin, where it was found, only in the upper course cf th.e Terou. - 18 - Flg. the site slte 9 ; Daily biting denslties at theKara River (at Landa pozand.a, siteK), the Alibori Iltver (at Riibori, c) in 19?9. M6 Rj-ver ( at Mô, site A, see Fig.11),B), at the Mekrou Iliver (Kêrenou, site J), ühe Bouli River (zougou,  -._,,^ $ril,il[-r^hh, r\ ^,v r,,, r ü N..cl llirr p., dot M6àMô t9? 9 o aC a at a lrrl Nc. cl llior por dcy fa.anor Âhbcri tcugcu i ::ir !iii ti .l I :! ,i,*7::;If,tl'î'" -19- Experimental treatments of potential sources have so far been the only successful me€uls of locat5.ng the origlns of reinvading biting §.damnosurn s.1o ( Garns et aI .19?9). fhe pattern of the reinvasion i.n the Togolese section of the OCP prouided an excelLent opportunity to repeat such a prograrne of experinental treatments. In particular the Togolese situatj-on was of speci.a-l interest since the najorj-ty of thc reinvad'ing flies were S.squ.a.:nosum, a specles with a lirnited d.istribution whlch caa be identified enzynatically and morpho1ogical.ly and. thus acts as a recogtlisable marker. Since S.squamosu.tr was frour experience i.n the west considered to be only a short d,lstance n'igrant ( Watstr et al. ,J.n prep.), tbe ain of the experimeatal treaünents was to check wb.ether this typc of reinvasion could be controLLed by a liuited extension of tbe treated êreâ. The experimeatal area of 198o therefore was d.esigaed rith the purpose of trylng to protect the Mô va-l1ey by treating s.squanosum breed.ing sites within a rangê of about 1oo kn of this vaI1ey ( Fig.tt ). Substaati"lj.aquamosum. breeding sites further south in the .â.takpame region were not incLuded ln the treatmeat areas as these mountainous reg:ions ale very èlfficult to prospect and se considered that they-nrighü pose serious technical probleas for treatments, rbich we did not have the Bea'ns at our disposal to overcome. It sas an int,eusioa of our experimenta. treatneats to determine whether it çoul-d be poseibJ-e to protect the Mô valIey rithout the aecessitÿ of treating the Atakpame region. The experj-mental treatments ia Togo were carried out for a period of 6 weeks beginning on 16 June 1ÿBo. unfortunately, in 198o, d,ue to cllnatica-1 reg'ioas .the reinvaslon began In earnest two weeks 3.ater tbaa ln 1979 and also fewer fl-ies were involved. This situation uade i.t nore difficult to interpret the resul-ts of the experinental treatnents. Apparently there ras a reductioa of about 5o % of the biti-ng densitles, however it beca.ne quiüe clear that the experinenta-l treatnents did not reduce the uumbers to sufficiently 1or Ievels to be acceptable. The only rel-evant breecling sites of S.squamosum of shich we are aware wbich could be potential sources of the continuing reinvasion in Togo are the upper Terou in Benln, the Mono downstrea.u of Landa-Mono, the BouvêLêrn, the Aniê river downstrea.n of Paga-Ia and the massive breeding sites such as the AsuaJcoko in the Atakpame region ( r.l,g. 12 ). Oa]-y the latter area is a Iikely cand,idate as a main aource since the nrlabers of S.squannosult breeding sites in the other areas were 1ow. ille have to e11= risage the possibility that large populations of S.squanosuu can i { J rfi r/ /x _fr ;ii,2,,i Fig.1o the $istribution of the cytospecies of the S.damnosum-complex in Togo and Benin based oî Ïtr-ffiIogical identification of ;, larvae collected during l"layrJune and July 1979( , ,III a , , , , , Cytolog:icaJ. identifi= cations carried out by Dr.VaJi-nc O S. damnosum tr S. sirbanum[f S.sgua mosum e S.soubrense E S.sanc tipauli ..... OCP bOundary , ---- Benin -Nigeria border T,L,Gou/1, )*l\/ t ) 1l:', \ --^..a.a..a..aoa.4..o.....a..^- a.)T LAMA-KARA t a t t ttaa aaraaa ft aII I tI I , ItIt\I ,t't , ,I , ,t @ Oaily catching site 50 km FIg. 1 l I ixperLmontal treatments of g.§guanosum1albreeding sl,tes eouth of OCP NATIlINGOU a a!. t --'.. T. tI al ol tl 'ltal 'l3r zt .t .\ .:::4! .J 3'rt .t '.r al .t ott.t "ltt/ ., .l 'ooo111io..... :i '..-. u.).' a a,l-!t..' '..{ : !,ii ! :§iù:aj , : io}E ':9. O 't 3 -er: it-t, z- ,/ a ,II a a , , , air .'Ii,irir .t it:, 't , , -- -- --2 t I :.. rï ., r.l ti r't :l rlvers treated experimenta].ly rivers dry on 4tu .ruty r 98o OCP bounclary Beai.n-NJ.Beria border Every Day Catchlng sitce Mô br5-dge Landa Poza:rda Bagan Fazao Landa Mono Tipaotl Zougou Gbassê Alibori Kêrênou Bêtêrou TAK?A a  B c D F G E J K L I , ,t , ./ 50 km . -22- regularly trave]. d.istances of at least 15o kn. For this reason it seems that the Mô val1ey cannot ue protected without treatlag such sources as the Atalcpame region. Considerations of any extensj-on of the protra,r,ne area therefore have to include the necessity to treat rivers in that 'region. Although we can be rather confident that this extension would suppress the reinvasion by §.-squamosum in Togo, it cannot be conpletely excluded that S.squanosr::n may come also frora breeding sites west of the Volta La-Ice, such as the Ta-i:r river a-nd, the Tanfi j.n Ghana from where it has been recorded ( vajine and Quillêvêrê 1g?B). But ühese rivers sould be covered by the pJ-anned exteasion in Ghana. Although Soseuanosum predoninates in the fJ.y populations reinvading the TogoJ-ose sectj-on of the ocP the iaportance of g.gæIg §.Etr. cannot be neglectêd si-ace it co'ntributes to about 24 % of the transnissioa potentialo Eowever, since tluls speciesf breed:i-ag sites are ubiqrritous souüh and south-east of the study area we cannot present J.ikeJ.y,source areas of the reinvasion by this species. The situation i.n Benin has not yet been compJ.etely a.ual.ysed. Ileavy reinvasions were observed L\ 1979 çhich partlcularly affected the Sota and Alibori basins. In contrast to the situatlon ia Togo lnvadiag fly popuJ-ations are al-most exclusiveLy S.da.mnosum, B.str./S.sirbanum. Enornous aad. highly productive breediag sites of savanna cytospecies rere found. south and south-west of the reinvaded areas in the Ouêmê river and several tributarLes. The high frequencies of strong rinds at 6.oo m fron the eouth aad south-west are coasi.stent rith the hypothesis that S.d,a:nnosrua s.str./S.sirbanum can migrate from these breed.ing sites into the OCP in Benin and Togo. the neteorologicaJ. conditions in the study area are therefore not a variant with the conclusions reached using the biolog'icaL infornations, and the generaJ. trends appear to be sin1lar to thr deductions of Garms et aI . (19?g) coacern:Lng the d.irections of reinvasions l-n the south-westera sectors of OCP. It sbould not be neglected that extremel.y productive breeding sites of §.damnosum 6.1c êre kaow to exj.st east of the progrerrune J.n Nigeria( Corsskey 19?9). Of particular interest for the OCP are the Niger and, its tributaries, as the O1i and the Moshl ( trig. I )..Ilowever, rithout having carried out experiroental treatmente in the southern parts of Benin which rould shor the importance of the Ouênê basln it is impossible to.predict to what extent control Beasureo l.n NigerLa ror.rld beneflt the controJ. operations of the OCP. FlE. 12 : Potential of ths OCP and the by S.squannosun souüh and. easteources of experimental. the reinvasion area of 198o §§, NAlrSrNCou ..5Ëiroaé \ rlvers withpredoruinantJ.Y S. squa.mosum sporadic occurrence of S.squamosum OCP boundary boundary of the experimental- area r-l 5ô km §\ I , ,Ifla.IIt\ I t :... , \:.:' Jr'.: L:._ -t t' .,.',tl:,.)ilu ,.::,. i'.:- ,:1.§ :§ .j: -.':(:. r ,:ii"j \--- \\r-rt' ù-24- coNctusIoNs 1. Areas of the OCP are bej.ng reinvaded by bl.ting females of thc S.damnosura complex orig:inating frorn breeding sites outside ühe controllcd zotlêr lhis reinvasion is an annual occurrence. Migrations of fl.ies are windsupported and cLosely related w:lth the northward movenent of the TTCZ ai the end of the d,ry season and the monsoon rinds rhich follow it. Appareatly novements of flies are across country aad nain].y in a SW-NE d.:Lrecti-oa. 2. Main componeuts of tbe reinvadiag f1y popuJ.ationa are the ea.vanna cytospecies§.@6.Stfo€u1d,S.sirbanrrn.Theiroccurrenceappeara to be nost noticeable up to &Lstances of ,oo km fron their aources, but occasionaL snaLL concentratLons of fJ-ics may appear up to 5oo kra awâÿr and it is possible..that a few rnay be caried further. t. A dlffereat typc of reinvasion was observed J.n logo rhere Soseüârosurtr was the predoni-nant species. Studies auggest that aLso this species nay travel dlstances of at least 15o km. Increased nrrmbers of forest speciee 9.sanctipauLl, g.gglggnse and §.yahense were onJ.y caught w:Lthin 5o kn of the prograrure boundary. Thls suggests that the flight behaviour of these species differs fron that of the aavanua epecies. 4. Iava&ing fJ.J.es appear to be older parous females Ean;r of rhich camJr infective Jrd stage J.anvae iadistinguishab3-e from those of 9.glvu}§. These fenales tend to bite close to the rivers. and do uot disperse ae far as normal popuJ.atioas rith a higher proportion of youuger fJ.ies. It1= creased nuqber,s of auJ.3.iparous flieE rere onJ.y caught closc to the boundaries of thc prog!âneêo 5. Experinental treatments to be the most valuabLe means rivers in potentia-l aource areae proved dLscriuiaate the eoulces of the rciavasion of to 6. The southeru extensj-on in Ivory Coaet (Phase IV, 19?9) largely EuppresËed the reinvaslon in Phase f ( Ivory Coast, Upper Volta) but had littJ.e or no cffect on the reinvasion i.n Ma.l-i. Most likeJ.y sources arê the headwaters of the Nlger and its tributaries in Guinea. 7. Control neasures in Upper Guinea probably would be of considerable benefit for restern areas of OCP çhlch are still exposed, to reinvasion. At present it is inrpoesibLe to predict rhether reinvadiug f1y popu1ations also originate from breeding sites in the Fouta DjaIIon mountains and further west. _2r_ 8. The S.squanosum reinvasion in Togo probably coull be suppreosed by a southern extension which should include alL br eding areas of thls spe ci es . 9. Possible source of the reiavasion due to savanna epecies in Benin is the ouêmê basj.n south a.nd souühwest of the reinvaded areas. However, flLles nay also orig:inate fron sources further east in Nigeria. At present it appears lapossibLe to predict the i.nportance of these sources. Ex= perimental treatments of the ouême basin sbould be carried out. -26- REtr'ERETCES CROSSKEyIR.w. U9?9) : An appraisal of current knowledge of §inulium .da:nnosum u.i. in the Fàera1 Republic of Nigerla in relaîfiFE-the AËffipnent of an onchocerciasis control campaiga. ÿrHo/VBc/79.?1?, wuo/onluo/?9.15o (unpubllshed clocunent), 75 Pp. GAEMSTR. «9?3) : Zur Verbreituag von Z.Tropenned.Paraslt. 24, 222-231 GAEMSTR., A.POST ?g56) : DJ-e Verbreitung von Sinuliurn damnosum in éuinear/We s taf rika. Z o Tropenne d . Paraéi t . 1Trc46- GARMSTR., C.G.VAJB{E (1975) : On the ecology and clistribution of the species of the Sinuliun Êgrygsgp complex in èifferent bioclimatic zone6 of Liberiffiffii;ffipenned.Parasit . 26, 1?548o GÀR!'{S1R.1J.F.WA.LSH, J.B.DAVIES U9?9) : Studies on the reinvasion of the Onchocerciasis Control Progra.mme in the Volta River Basin by Sinulium daranosuo soI. *1!h enphasis on the south-western area.6.trol'ffi ,tFaîEffio, 345462 GARMSTR., R.A.CIrEKE; M.KERNER (1979) : A study of the re-invasioa l.n the south-eastera ateas of the Onchocerciasis Control Progra-mme. rJlorking Group on Re-invasion, Ouagadougou, 13-15 November 1979t(unpublished working paper) 64 pp. GARMSTR., R.A.CEEI(E, M.KERNER 1198o) : StuùLes of the reinvasioir ia Togo and Benin in 198o. PreLj.roinary report. (r.rapubli.shed report) TOWNSON, E. : Identification of Sinulium 1!ryg ".1. from thcOnchocerciasis Coatrol Progranme area by clectrophoretic nethods . (19?9)(unpubLished reports) VAJIMETC,G.l D.QIiIILÊVERE OSZS) : The clistribution of the Sinuliun da-mnosum conpl-ex in West Africa çith particular reference to the dn;fficerciasis Control Progranmê area. Tropenmed.Parasit. 29r4?t-482 WALSHTJ.F.l J.B.DAVIES, R.Le BERRE 0979) : EntomoLog:ica1 aspects of the first fi-ve years of the Onchocerciasis Control Progran'ne in ühe Volta River Basin. Tropenmed.Parasit. 3oJ28+44 WALSHTJ.F.l J.B.DAVIES, R.GARI,IS : The Onçhocerciasis Control Progtarnrnc ln the Volta River Basin : the effects on the vector Sinullum @s.1.of.nextensionofcoatro1actirritiesintosoutberaÏvoæoast during 19?9. (in prep. ) lvAI,sllrJ.F.l J.B.DAVIES, n.LE BERRE, R.GARMS ('.tgz1) : standrardizatioa of criteria for assessing the cffect of Sinrüiun control 1n , onchocerciasis control prograone§. Trans.roy.Soc,trop.Med.Hyg. 74 6Zy-626 WEO (19?3) : Onchocerciasis Control Ln the Volta River Basin ârêâo Reporù of the Preparatory Assistaace ltlssioa to the Governments of Dahoney, Ghana, Ivory Coast, MaLJ.r Togo and Upper Vol-ta subnitted' by TINDPIFAO'IBRD a-ud WHO docuneat OCP/?1.1 WHO (lgZ8) : Onchocerciasie Control kograrnme in tbe Volta Rlver Basirr âleâo Evaluation RePortr Part 1. Sinu].ium damnosum in Liberia. $ I i ; f. t- ,, : F br llt-F i i t.P Ë" k Fi P.I!b h Fb E EIt B Ex Ë xF F P E T"§ ,. ÊÈÉt: : Y [: