Eradication of the vector simulium neavei from the northern onchocerciasis focus of Kabarole district in March 1997

Eradication of the vector Simulium neavei from the northem onchocerciasis focus of Kabarole district - Situation in [Ilarch 1997.] by R. Garms, Bemhard Nocht lnstitute for Tropical Medicine, Hamburg, Germany Abstract The northem onchocerciasis focus of Kabarole distric't is mainly located around the ltrarara forest reserve. The main focus is not completely separated from two smaller secondary foci on the Siisa and Asara river systems further east. Simutium neaveiis the only vector. Ttre dynamics of the transmission of Oncheerca volvulus by the vector have been studied since 1991 to assess whether the community based distribution of ivermectin in a small and isolated focus can sufficienfly reduce or possibly even intemlfl the transmission. The ivermectin treatments had a clear effect on the in- fection raies of the vector population, which dropped from more lhan 4Oo/o before the treatments to 22o/o in 19g1. Hortever, the'transmission remained high. DNA probes confirmed that more than goo/o of the infections canied by the flies were o. votvulus. A vector control progEmme taas begun in 1g94 to examine whether onchocerciasis control in the focus could be enhanced by a combina- tion of ivermectin treatments with veclor control. When first experimental treatments of the Sogohi river using the larvicide temephos rendered good results, measures rivere gradually extended. By the end oitggs plans were made and pursud to eradicate S. neaveifrom the whole focus. so far results of the eradication campaign were very encouraging. No flies vrrere caught anymore since 16 months at the routine catching sites Kijura d'am and Sogohi river. The annual transmission poten- tials which ,aere estimated to range from 4500 to 6500 infective larvae of O. volvulus per person f-r y""r in 1992 have fallen to zJro. About 900 crabs wtrich were examined in 1997 from various tf,e61points of the main focus r,rrere all negative. Treatments of rivers in the ltrarara main focus have now been suspended. There was also no evidence of any breeding in the Siisa.suFfocus' However, since tyr1.9 flies vnere caught in March treatments of this river system will continue for further three cycles untii the end of Jine 1997 together with those of the nearby Asura river, where er:adication ,n"a.rr"" began in March 1997. A rrvo*ing plan to monitor the focus after the suspension of vector control measures and to prevent a resurglence of the vector population is proposed for the period 1997 to the end of 1998, wlren the present phase of the GTZ Basic Health Services comes to an end. lntroduction There are ttr'/o active foci of onchocerciasis in Kabarole district, one in the north, bordering Kibale district, and a southem focus, which continues into the districts of Bushenyi and Mbarara (Fig' 1). Simulium neaveiis the only vector in both foci. Some onchocerciasis still occurs in remains of a third focus on the Mahoma river south of Ruteete, where the vector S. neaveihas disappeared fol- lowing deforestation. This report will primarily deal with the northem focus, will shortly summarise tne siudies on the vector carried out since '1991 and review the present stage of the vector control and vector eradication measures launched in 1995. Furthermore, a rrrlorking plan will be proposed for the period until the end of 1998, which is the end of the present phase of GTZ Basic Health Services Project. No vector control had so far been carried out in the focus. Onchocerciasis control was only based on the community based distribution of ivermectin, which began in the second half of 1991. The ivermectin is distributed by the Basic Health Services of the district and given annually, with part of the area experimentally under twice yearly treatment. lvermectin is a microfilaricide which reduces the microfilaria reservoir available for the vector population. Detailed studies were therefore canied out.since 1991 to assess whether the treatment schemes have an impact on the transmission of Onchrcerca volvulus by the vector S. neavei and, in a small and isolated focus, can reduce or possibly even intemlpt the transmission. After four ') Report to GTZ Basic Health Services, Fort Portal' 31.3.1997 2 3 FEV. 1998 2years of ivermectin treatments infection rates of the fly population were significantly loriver than at the beginning of the ;;p;i6, Urt tn" transmlssion tia's ititt trigfr. Plans rrrrere therefore made to examine whether the control of onchocerciasis tn the area could-be enhanced by a combination of ivermectin treatments with vector control. First experimental treatments on a section of the Sogohi river using the larvicide temephos-(Abate O ic"nl"O out in the second hatf of 1994, had an iilmediate effect on the fly poputation. Results were so encouraging that controt activities u/ere soon extended to further rivers in the rrvest of the focus. ln view of the difficutt terrain and limited resources, at that time, it was not thought to.be fea- sibte to cover all Ure"Oing rit.r. H"n"" the scfreme was only designed as a c.ontrol Prolect aiming at an interruption of the tra-nsrnission. Horvever, in view of the excellent results, and after the group had learned hour to move in the forest, rn nugust 1995, a plan was developed to eradicate S' neavei from the wtrole of the northem onchocerciasls focus' From the beginning, ln 1990, the proiect ufas a cooperation betvveen the Bemhard Nocht lnstitute for Tropical Mediclne ln HamUurg', Germany, ttre Gtz gasic Health Services in Kabarole District and the Vector control unit of the Ministry of Health at Fort Portal. The area Most of the northem focus is located around the ltwara forest reserve about 25 km north-east of the district capital Fort Portal. The reserve "o*tt 87 km2 of steeply undulating terrain and Is bordered to west, south and """t ui large tea estates which are highly iririortant economically' To the north it is bordered by subsistenie taims with some laige cattte.iarichei along the lower sogohi and Muzizi rivers. The area i" J"n""fV p"pulated "nO onino"erciasis is highly-endemic'.About 80% of the populalon of a5,0oq iirin'g b6und the ltwara Forest Reseruels estimated to be lnfected with 0nchocerca volvulus. The ltwara focus is not completely isolated from two smaller secondary foci on the Siisa river sys- tem and the Asrya rlver to tlre east. The Silsa river area is mainly of a savcnn" !Vp" with subsis- i"n"" t"rring and larg; ;ti6fi"h reaching the Muzizi river to the north. There is'little forest left along the streams ,niil. iurprising that S.-neavei can still survive in the area. Most of the Asna ,ir"r-p"6". through forest or 6orOers forest reserves to the east. lts lower section is in deep forest (Muhangi forest reservel. nftogether about 37.000 people are believed to be infected ln the whole northern focus (J. Bamuhiiga pers. Comm.)' Distribution of the vector Simulrum neavei s.str. is the only vector of O. volvulus in the focus. lt belongs to the S' neavei group of species lSubgenus tewisenum1, which develop in. an obligate phoretic association with river crabs. The crab potamonautes aloyslsa baudiae is the phoretic host of s. neavei in both foci of Kabarole district. Extensive sun eys were conducted since 1990 and large numbers of crabs were examined to map the distribution of the vector' The distribution of breeding sites of s. neavei prior to the onset of the control and eradication measures is shown in figur;2. ln the area of the ltrarara forest reserve the vector had its breeding sites in the Sogohi river 5nd its main tributaries Wamise, Nyakibuguta,.Kanaba and.,Kafunda' ln the Sogohi breeding continues north of the forest downstream to the confluence with the Muzizl river' which drains into Lake Albert. East of the ltwara forest s. neavei breeds in the siisa river with its tributaries Kyasa and Mohabura and in the Asaa river' surveys of the Aswa river were only completed in.March 1997. No breeding was found near the bridge of the Kyarusozi-Katoke road, wnicn is just downstream of large papyrus.sl 'amps and where the oxygen content & the water is still low. First breeding starts aboui 1.5 km below the bridge' The infestation of crabs *r L*ti"rnely high rurtner downstre-am where the river enters the Muhangi for- est reserve and continued down io the confluence with the Muzizi river (Table 3). - The occurrence of onchocerciasis in the area of tne uruiiiiJ"i-e.t"t"r in Kibale District is probably due to the transmission by flies *ni"n f,ru" their Ureeding sites in the lower Aswa river' No S' neavei breedlng asites were detected in tributaries of the Asjlra wtrich are either too small or unsuitable because of targe papyrus $iramps (e.g. Muconda, Musabira). No brceding sites urere found in the Nyabukoni riv6r flrtfrer east of the Asira which is largely covere'd by papyrus and unsuitable for S. neavei. The Mr.rzizi is the largest river in the area and forms the boundary uetupel the districts of l(abarole "nJ KiO"t". Long strErcnes are swampy, covered by reeds or papyrus, lack any orygen and are un- suitable for the development of S. neaver. At Hoima bridge the orygen-content.ritras found to be practically zero. We do not expect any S. neaveibreeding downstream from Hoima bridge to the confluence with the ns,na river, where the orygen content was still extremely loiv (0.6 mg/l). Simi- larly there will be no breeding from the Asara downstream to the Siisa confluence. So far immature stages of S. neayei were found only once in the lorirer parts of the Muhangi forest reserve near frfu1[fy, (in March 1993) and furtheidown near the confluence with the Sogohi river, where the in- festation of crabs was always low. Since the Muzizi could serve as a link betrrveen vector popula- tions breeding in the Asu€, Siisa ana Sogohi rivers, more detailed studies rrere canied out in March 1997. Altogeiher 295 crabs from the Muizi urere examined in March 1997, which were all negative, except one empty pupal case on one crab caught below the confluence with the Sogohi. lt is possi- ble that the S. neaveipopulations of this river are not stable due to the adverse ecological condi- tions and depend on strong populations in the tributaries. During the 1970s, S. neaveialso occuned in several streams draining wesilurards dorn the rift val- tey eiarpment into the Toro Game Reserve and to Lake Albert, according to Vector Control Divi- sion recoids. Apparently breeding has ceased there in recent years. Repeated checks which were canied out annually sinie 1991 have revealed neither S. neaveinor crabs. This was confirmed by a special study canied out in the Kijura area by J. Mpagi (9m), who could shour that biting by S. neaveiwas iestricted to the direct vicinity of the e ltwara Forest reserve and no flies occuned near the rift.valley escarpment. The reasons forthe disappearance of both flies and crabs are unclear (Garms et al. 1991). Transmission lnvestigations of the dynamics of the transmission of O. volvulus by S. neavel were begun in 1991 in ordei to assess the effects of the community based ivermectin distribution, which was launched in 19g1. lt was the main objective of this study to find out whether, in an isolated and limited focus, routine treatments of the human population alone, would reduce or even intemlpt the transmission or whether a combination with vector control measures should be rrpmmended. Well organised full day (11 hours) catches at weekly or fortnightly intervals needed to estimate an- nual biti-ng rates (ABR;sjanO annual transmission potentials (ATP's) could not be canied out due to a lack of resources "nd fo, various logistical reason. Female S. neaveivrrere routinely caught by localy employed vector collectors at three catching sites Busasa, Kijura dam, Sogohi bridge south' west Lnd easi of the ltwara forest reserve and one catching site on the Siisa river (Figure 2). The vector collectors are working for about 8 hours per day on 4 days (Monday through Thursday). Hourly collections, intem.rptio-ns by rainfall etc. are recorded on catching forms. About once a month a full day catch superviseO Uy the entomological field staff of the Vector Control Unit Fort Portal is canied out all sites. Flies are brought alive to the laboratory, where they are aged and examined either fresh or atter staining for infections with developing (L1lL2) and infective larvae of O- volvu- /us (L3). No sound pre.treatment data are available because the transmission studies only began ttrvo to three month before the onset of the ivermectin treatments. There is no doubt that the transmission was very intense and infection rates of fly populations extremely high prior to and at the start of the ivermectin treatments. At the three catching-stations around the ltwara forest annual transmission potentials (ATP's) were estimated to reach 4500 to 6500 infeclive larvae of O. volvulus per person per year. dt ZOS'parous females of S. neayer, which were examined before the onset of the iver- mectin campaign, 4Oo/oweg harbouring first and/or second stage larvae (L1ll2). It was the general pattem that shortly after the distribution of the ivermectin infection rates of the fly populationi dectined sharply but increased again two to four months later. This is shorvn by Fig. 3 ioi tn" example of flies citight at Kijura dam-, where infection rates with LllV of O. volvulus d* 4creased and increasd in relation to the ivermectin treatments of the human population in neigh- bouring communities. tn 1991, of a total of 1553 parous flies from all catchlng sites in the northem focus 2Z.A% canied lsU2nd stages (L1ll2) ol O. volvulus and 2.60/o third $age larvae (L3) in the head. Conesponding figures forlhe following years were 6U1t31.015.6 in 1992, 3990/26.8/3.50lo ln 1993, 3}17li1.glg.itn-tg94. As had to be expected infection rates of the flies rivere slgnlficantly lorer than they had been before the treatments, but it became clear that at least for the flrst three years of the piogramme the transmission could not be reduced sufficiently. Thls was also shown utren the indlvidual parasltic Ioads of the infected flles with LllV or L3 vrere comparcd, wttlch trvore 9.U4.8 tn 1991, 9.9i4.9 in 1992, 9.6/4.9 in 1993 and 8.814.7 in 1994. lt was estimated that 100O parous flies canied 124 lnfective tarvae of O. votvutus ln their heads in 1991, 276 ln 1992' 169 ln 1993 and 176 in 1994. Due to the success of the vector control activlties wfrich began in the second half of 1994 transmls' sion studies had to be discontlnued ln 1995. Horriever, data from the southem focrrs (Klcheche) in Kabarole district clearly demonstrate that still in 1997, atmost 6 years after the launching of the ivermectin campaign the transmission was intense. Of 115 parous S. neaveiwhich were dissected by the Vector ionlrot Unit in January 1997 48 (42%ol were Infec'ted and 11 flies had a total of 54 infective larvae in their heads (470 per 1000 parous flies). ldentity of filarial infections found ln Simullum neavel ln order to evaluate the effects of the community based lvermectin treatments on the transmlssion it was important to know if all infections found in the flies were O. volvulus, or if morphologically similar Onchocerca spp. of animal origin , or non-Onchocerca filarial larvae also occuned. ln par- ticular lt had to be as#ssed whether lnfections found in vec{or populations after the human popula- tions had been treated with ivermectin rrvere still O. volvulus, or something else. During routine dis- sections of fresh S. neaveifilarial larvae found in the flies were dried on slides and the DNA later extracted for a PCR based on a 150 bp repeat sequence whlch is present ln many Otrchocerca species. Altogether 259 out of 395 samples could be amplified, 92Yo 1239) of them reacted with h^ro O. volvulus specific probes, but none with a probe specific for O. ochengi. At least 9'lo/o (411of 44 S. neaveiwhich had lnfective larvae in their heads were infected with O. volvulus. Samples wttich did not amplify were mainly from infections with only one or two larvae, which were possibly lost during processing or from which the D|.lA was not sufficiently extracted (Fischer et al. 1996). Results provided clear evidenie that the vast majority, at least, of infections found in S. neavei urere indeed O. volvulus. Furthermore, in vievrr of the very high natural infection rates of S. neavei populations, it can be concluded, that S. neaveiis highly anthropophilic. Vector control and vector eradication in the northern focus Preliminarv exoerimental treatments First experiments r,vere canied out on the Sogohi river in 1992 and again in 1994_i1 order to test whethei the trrlo insecticides, the organophosphorous compound temephos (AbatelD)) and the bio- logical larvicide Bacittus thuringiensi sero$pe H-14 could be used for the contro! of S. neavei. Both lafuicides have been widely and successfully employed over more than 20 years in the WHO On- chocerciasis Control Programme (OCP) in West Africa. They are considered to be harmless for the environment and can be used freely. lt had to be examined whether thgy would be equally effectlve in breeding sites of S. neavei in weslern Uganda, which have particular ecological conditions, e'g' lo,ar dischaiges (mostly less than 1 m3/sec), iow temperatures (below 20"C) and a sluggish flow. It turned out that a concentration of 0.1 mg/l (=ppm) temephos (calculated for a river discharge of 10 minutes), which is normally used for the control of S. damnosum s.l. in smaller watercourses in West Africa, also had a good effect on S. damnosum s.l. in Uganda, but did not kill al! larvae of S. neavei over sufficient distances. Further experiments were therefore carried out with concentrations from 0.2 to 0.4 mgl/1, which rendered good results. tn larger watercourses as the Sogohi and Aswa rivers concentrations of 0.2 are now used at higher and 0.3 mg/l at lorrver discharges (less than 1 m3/secy. The smaller tributaries had to be treated with a higher initial dosage in order to ensure a 5sufficient carry kuse, in vieu, of the very diffictlt tenain, the number of dosing points had to be restricted. ln general, in small streams a minimum amount of 30O mlAbate@ (=60 ml temephos) or 500 ml in larger streams was applied at each dosing point. ln some cases, according to the results, the dose was later reduced to 200 ml, or had to be increased to 500 ml, when the insecticide did not reach the next accessible dosing point. Most of the streams, where S. neayei breeds, pass through stretches with very flos, with muddy, clayey beds or through dense vegetation, wtrich causes a rapid loss of the biodegradable insecticide. There was no sign that crabs urere affected by the te mephos. ln aerial operations as in West Africa the full amount of Abate@ is usually applied unmixed in one drop. ln ground larviciding it is necessary to apply each dose over a period of 30 minutes to ensure adequate mixing in the river water, especially wfren breeding sites are not far downstream of the dosing point. The larvicide was dispensed from a knapsack spayer, being pr+diluted with river raater to about 15 to 20 I to provide an adequate volume of liquid. Experiments with Bacf/us thuirqiensis H.4 vvere less convincing due to an insufficient carry. This biological insecticide tends to settte rapidty wfren the flow is sluggish. ln order to ensure an effect it urould have been necessary to increase the number of dosing points by several times which is not practical. Bacillus thuringiensis H-14 may eventually r,vork in areas where S. neavei breeds in streams with a continuous slope and a turbulent flov (e.9. possibly in some tributaries of the Kitome river in the southem focus). Control of Simu/rum neavef in the northem focus First treatments of the Sogohi river (3 August, 14 September 1994) were folloured by an immediate decline.of biting densities of S. neavei at the catching site Sogohi bridge (Fig. a). Fly densities re- mained loru for at least two months. A further treatment in February 1995 again lead to a significant reduction of biting densities with a clear effect over 4 months. ln view of these promising results, from June onrirtards the treatments were gradually extended to the main breeding rivers of S. neavei in the ltwam focus. About 20 dosing points rnere selected along the rivers Sogohi, Wamise and tributaries. Treatments canied out from June to August 1995 lead to a virtual disappearance of flies from the routine catching siias Busasa, Kijura cjam and Sogohi bridge (Table 1). The eradication proqramme ln view of the excellent results of the vector control measures plans rirrere made, in August 1gg5, aiming at an eradication of the vector from the wtrole focus. Minor amendments of the time table(Table 2 ) and the map of dosing points (Fig. 5) became necessary in early 1996 after breeding sites of S. neaveihad been detected in an upper branch of the Sogohi river (Sogohi ll) and the Mo- habura (a tributary of the Kyasa river). Dosing points on the Asaa river had to be increased from three to five. Finally, plans to treat the Muzizi river at two dosing points below the confluence with the Siisa river could be abandoned in 1997, when no active breeding sites could be detected. The eradication programme started in September 1995. lt included all knorrun breeding rivers of S. neavei in and around the ltrarara forest and the Siisa/Kyasa system further east. There was a set- back of the operations when, due to a late anival of a new shipment of Abat@, river treatments had to be reduced or intem.rpted from March to August 1996. For logistical reasons the treatment of the Asara river had to be postponed to March 1997. The larviciding measures had a dramatic effect on the adult populations of the vector. Biting densi- ties dropped to practically zero at all routine catching sites. At the catching sites Kijura dam and Sogohi river (Table 1) the last females of S. neavei were seen in November 1995. At the catching site Busasa single flies were occasionally caught until June 1996 probably due to an invasion from nearby breeding sites of the upper Sogohi, which received first treatments in April 1996. Trarc flies were caught on the Siisa river in March 1997 which possibly came from the nearby Asalla river, which uras first dosed in March 1997. Last infective flies were caught at Sogohi bridge in October 1994, at Kijura dam and Busasa in July 1995, and on the Siisa river in August 1995. Although treatments of several rivers of the westem part of the ltwara main focus r,rere discontin- ued already by the end of 1995, they were never re+olonised by the vector. After last positive crabs t*ere seen in the Nyakibuguta in August 1995, the river received the last treatment in D+ i, .:- :1 :Y _1 6 cember 1gg5. All 47g crabs from its main checkpoint (Fig. 6, No. 10), wtrich vuere examlned ln 1gg6 and 1gg7, rnrere n"g"tir" All 1683 crabs fromthe ltrnraia main focus, the Siisa system an!.]f9 Muzizl whlch trer" er"rilned from January to the end of March 1997 were negatlve' excepl that one crab from the Murlzi beldihe sogoticonfluence carried one single empty pupal case (Table 3). Asthelastphaseof theprojecttreatmentsof theAsarariverbeganon4 March 1997. lnvlewof the low dischaige (0.6 myieci treatment was canied out at a concentration of 0.3 mg/l (=6F m! nUateOl. Ttireedosin;p"i;it"r*ie not sufficient to treat the wtrole river. For the second treatment "Vai (iqns March tg:97) ttre number of dosing points had to be lncreased to five. For the project 100 litres of Abate @ and 50 litres of Baciltus thuringiensis H.-1! ha!. been purchased by the ti"1nf,"rO Nochi lnstitute, and 150 litres of Abate@ by the GTZ Baslc Health Servlces' A to- tal of about 13S litres of Abate O tras so far been used for the vector control and eradlcatlon meas' ures in the northem r*rc, 3.8 ln 1994, 56.3 in 1995, 61 in 1996, so far 13.6 I in 1€97' lt ls esti- mated that for the last routine treatments (3 cycles) about 25 litres will be needed' The remalning stock of roughly 70 fiiies of Abat@ should be sufficient to retreat singte rivers in case thls should become necessary. Reassessment of the situation in March 1997 The state of the eradication measures has been re-assessed in March 1997' Itwara main focus Most of the key checkpoints were prospected at least once from January to the end of March 1997' About g00 cratis were examined which rivere all negative (Table 3). No flies were caught at the routine catching sitesBusasa (last s. neavei seen 17 June 1996)' Kijura (tast S. neaveir""n it November 1995), -sogohi (last S. neavei I November 1995)' Additional su- i"*ir"o catches *i"."iri.o out at thiee sites near Akanyege (southcastem flank of the focus) on 11 March 1997. No flieswere car4ht. All routine treatments of rivers have now been suspended. The last treatment was on the Sogohi north of the lturara r*Jrt in February 1g9i, where one positive crab with a single larva had been detected ln November 1996. Slisa rivgr sub-focus Rivers Siisa and Mohabrura were prospected several times since January 1997. Altogether 494 crabs upre examined, wtrich rrvere all negative (Table 3)' Three supervised catches nvere canied out, one each in January, Feluary and. March' No S' neaveiv,rere caught. Hou,ever, the vector collectors caught one single s' neavci in March 1997' which was the lirst fly since i+ September 1996, and i second fly was caught..later on the Si- lsa/Kyasa connuenceizi rrrltcnl. ri9 siisa system.can be.easily invaded from the nearby Asla ;ir";:'*# ti"rt,*"tbnry U"g"n in March 1997 and biting densities are stillhigh' Asaa river crabs from the Aswa river were highly positive as had to be expected (Table 3), since first treat- ments of this river only began on 4/5 March 1997' No organised fly catches were carried out near the Aswa river. However' numerous flies u'ere en- countered during tne prospection of breeding sites. lt can be assumed that biting densities are hlgh in the area. Conclusions All results suggest that vector populations are now on a very low level and S' neaveihas virtually disappeared from the ltwara main focus. Hov,rever, they do not allow the conclusion that the fly 't population is already extinct. s- neaveiis a very vulnerable species. when under the pressure ofcontrol.measures populations wilt rapidly drop below the threshold at wtrich they can ue easiiy a+tected by means of fly catches on human bait or by the examination of crabs. The threshold atwhich the vector can no longer exist and the populati6n wtil coilapse is not known. Therefore, on theshort term it will not be possible to assess whether the vector poputation still exists on a low level orhas been eliminated. Earlier control projects, e.g. in G-glabngo forest areatr west uganaa,have shown that s. neavei can be eraaiiatea ev6n with anincomptete covetage of the fo"ffbt;process of attrition (Prentice' 1974).lt is ho@ that this may also happen in thJ northem onchocer-ciasis focus of Kabarole district . Although ihe larvicid. ,'"fo-i" considered to be harmless for theenvironment it r,rould not.be justified to iontinue with the treatment of rivers, wfren there is no d+tectable target. lt will be inevitable to monitor the situation over a longer period so that immediateaction can be taken in case single crabs carrying tarvae or aortt flies should occur. since s. neaveipopulations rebuild only very slowly and do no-t tena to spreaa there is no risk of a sudden r+infestation of larger parts of the focu-s. Working plan for 1997 and 199g Northem focus Routine tieatments of rivers Treatments of the Asrlla river should continue at intervals of four weeks at five dosing points untilJune 1997. A thorough prospection will be necessary towards the end of the operation to securetfrt !!q fly population has been eliminated. Togeth6r with the treatments " rrp"rrir"o fly catch should be'carried out at one site (the Tourists' foint, Fig. 6, Checkpoint No. 26j *here access isgasv' .T[e gauging and the treatment of the nslrra rivei wili requiri ttvo workini days per month(Day 1: Gauging and treatment of points No.31,32. Day 2treatments of points No. 33, 34, 3S). Treatments of the Siisa system shoutd atso continue on a reduced scale at intervals of four r,reeksuntil June 1997. Preferably treatments shoutd immediately follow the treatments of the Asara river.There tlES no evidence of any active breeding ciuring the first tnree monin;;ithG year. However,two flies were caught on the siisa river in naaich. Siice the Asrara river, where treathents only be-gan in March this year, is.not far away there is the danger of a Lontinuous re-infestation of the siisaarea, in particular during the rainy seison, by flies mig-rating -t-ng tne galleries oiiiiuut"ri"s or viathe Muhangi Forest Reserve. Treatments or ine siisa iystefi wrir rhuiritwo *oriing orv.. lf nothing unforeseen happens all routine treatments of rivers in the northern focus can probably besuspended in June 1997. The whole focus should be regularly monitored until the end of the present phase of the GTZ BasicHealth Services Project at the end of 1998. lt is proposed that ail key checkpoints 1Fig. 6, Table 4)are visited at tuo months intervals in 1997 and, in case the sites remain free of S. neavei, at inter-vals of three months in 1998. The visits can be spread over the two or three months respectively.The Days of Table 5 are interchangeable. crabs should be caught in the usual *"v ,no examinedfor immature S. neayel. - i The prospection teams, at least when going to remote places, should carry the spraying equipmenttogether with some insecticide. ln case poiitive crabs are detected the section of the river shouldbe treated immediately, and treatments repeated twice at monthly intervals. Flv catches supervised fly catches should be canied out at least once a month at the four routine catching sitesBusasa, Kiiura dam, Sogohi bridge and Siisa river, which are operated since 19g1. Further unsu-pervised catches which, at present, are performed four days a week should also continue, in orderto increase the chance to detect single flies. Past experience has shown that, at least at some ofthe sites, vector collectors became less reliable. Unexpected supervision will be necessary. Southern focus (Klcheche focus) Transmlssion I No vectoicontrol measur", ji" ptanneu so far for the sourhem focus (Kichech, lTY:)' Horuever' it would be hlghly desirable to further monitoiiire tnfectlon and infectivity rates of fly populatlone at the site Kitomt br:oge ((iar.rllei;i,in order io "rr.o tt e impact of the lvermec'tln distributlon on the transmisslon. For the iijG v"..i tnere nas ueen only a lir;ited effect, hovrrcver, it rruould be lmpor- tant to know, whether there is an effect on the long run' Prosoec'tion of breedinq sites lnfestations of crabs wilh lmmature s. neavei in the Kitomi river are extremely high. Monltoring of this slte will not be necessary because, wittrout vector control, no change can be expected' H-otw- ever, (rccaslonat prosfciLni oisit"s rfong in" Nkurungu and NyamusrviSa.rlve.l rirrould be of ln- terest. According.to our findings of the last-years s. neivei is on the retreat ln this area following rapld deforestalion and cultivaiion. The NfJ,'ungu/Nyamuwviga system can be regarded as a sub' ioirs possibly isolated from the Kashioha-Kltomi main focus. Acknowledgements The work had been impossible without the continuous support of the former and present team lead- ers of the GTZ Basic Health Services projfi Dr. Walter kipp ano Mr' Tom Rubaale' the onchocer- ciasis-Co-ordinafor Mr. J. Bamuhiiga, Dr. A. kid, and the dtZ staf at Fort Portal and in Kampala' rr was a great experrenc" ioi me t6 work 'iiiin in" eiperienceo and highly motivated entomological field officers of the Vector Control Unit fort portal, ihe late M. Androvole' E' Cakira' J' Katama- nywa, E. Tukesiga, .1. wamani and J. vocila. i ", dtit"rrltojvlrs' M' Kerner and Mrs' M' Badusche for their assistance in the field and ln ttre lauoratori6s at Fort Portal and ln Hamburg. I want to thank Mr. A.B. Kamanyire, the officer in cnarge-oflfre fGg.Fgrest Reserve for his very friendly ce' orreration, advice and guicrance. r am rnoluteo to the Ministry of Hearth of the Republic of Uganda for allowing me to carry out the researcn ano tr,e control of itre vectors of onchocerclasls ln west Uganda. Table 1 Numberc of flies caught at catching sites Busasa, Kiiura Sogohi and Siisa before and during vector control/eradication measures (cf. Fig. 2lor location of sites) Busasa Month 1994 1995 1996 January 312 827 0 February 262 333 0 March 4U 720 3 April 672 919 2 May 624 450 0 June 500 430 1 Julv 260 187 August 49 18 0 September 373 4 0 October 337 12 November w 3 December 365 1 Total 4982 3904 6 Month 1994 1995 1996 Januarv 96 19 0 February 99 7 0 March 428 6 0 April 348 1 0 May 396 2 0 June 311 24 0 July 123 3 0 Auqust 312 1 0 September 151 0 0 October 14 0 0 November 23 1 0 December 89 0 0 Total 2390 64 0 una 1994 1995 1996 974 743 0 632 514 0 7ffi zffi 0 292 250 0 606 315 0 6s2 277 0 193 159 0 325 11 0 78 1 0 431 I 0 283 1 0 81 0 0 6403 zffi 0 Siisa 1994 1995 1996 148 428 1 187 387 16 740 316 0 337 111 16 360 149 2 571 751 5 121 391 6 217 303 2 1M 10 1 72 4 0 4 2 0 26 3 0 2927 2855 49 Table 2 Time-tabte for the eradication of simulium neavei from the northern onchocerciasis focue of Kabarote district and average amount of Abate needed (cf. map Flg. 4 for the location of doslng polnts) (letsnendment ti{ch 1997)) !nsectlclde Abate ltr km by car Hours walk manl dayeDay Rivers Teamlstaff) Dosing points 123 0,95 70 5 5Day 1 Kanaba.lorer 2el 45 1 5 Day 2 Nvakabale Wamise 1(al 67 1 60 6,5 5 Wamise 2Ql I 0-E 5 Day 3 ,^lrihr rar rla 1(.?l 910 !p 80 5 5 Nvakibuouta. lotrer 2(21 11 0,3 3,5 Day 4 Soqohi 1 (3) 12 13 3 100 ,6 5 lorrver Sogohi 2(l 14 1.5 0 Dav 5 ifi;i; n Nr.rniroha cfl 1 (3) 15 16 ?2 120 4,5 4IITo-ioo middla 1 (3) 17 18 1,6 150 5 6Day 6 Kafunda 2223 0.6 3 4ztzl Dav 7 E]^xilnt.ralzudci nfl ' Snonhi 2 1 (3) 1920 1,7 100 6 minl 1 (3) 21 0,3 80 6 4 1(P.l 2425 0,65 150 2 5Day I Siisa Kyasa 2Ql 2627 0,6 2,5 Day 10 Mohabura: Siisa/KYaqq c'[!,- 1.2Q} 2829 0,8 140 1 5 lourer Siisa 30 0.5 2,5 Day 11 rainn mini 1 (3) 30 1 200 1 5 1 (3) 1+2 31 1 5 ,\SVlrElr U[' lYlUUUllu.t vrr. 33 1 150 1,5 5Day 12 Aswa. middle, MParo A Aslua. lo\,,/er. Tourists Point 1Ql 34 1 1.5 I^ tri'rhanni Enraql Res. 2Ql 35 1 4 22,8 1400 91,5 58 I OfaI per lrea{llellt uyurE 136,8 8400 489 348 Table 3 Collectlon and examanatlon of crabs from tfie northern onchocerclasis focus January to March 1997 Rhrrt 8tb I).b llumb.. o, crrba llumbrr of ;.ught l+yr l.vt Lrnrr lPuor lelrr Tobl Itwrre mrln focur SIl.. tub-focsr Arwr tub-focur IurIzI rlmr rll focl 2225 89a 191 512 ,o( 230 0 0 229 I 1 995 89.1 49.1 3r3)cl al1 0 0 671 a 10E 0 0 108 0 zt3 0 0 272 Nyekebal€ E Nyrkibuguta Sogohi ll SoCofia ll Sogohi Sogohi Sogohi Wamisa 2rd trib.cll old bridgc rntry ponl fool bridge lowcr low6r Nsuiga q,l.A Nluiga dl.B 3E r30 21 17 ,t8 23 15 21 1t 31 sl 0 0 0 0 0 0 0 0 ol ol si ol ol sl 0 0 0 0 0 0 0 0 0 0l oi ot ol ol ol ol ol sl 0 0 0 0 0 0 0 0 0 0 ol ol ol ol ol Mohabura lenfry pf Siisa lAlfrEd's disrittery Siise lAlfrrd's dhtilerySiisa lnftco's oistttcrySiisa lAtfEd's disritterySiisa lKatechist's placoSiisa lKyantonl citSiisa lKyasa at.Si:sa lKyasa ctl.Siisa llower ctt tnb.E c{ tnb.E cf, tnb.E 1km 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ol ol OI ol ol 0 0 0 0 0 0 0 0 0 0 0 o Aswa Aswa Aswa Aswa Aswa Aswe Aswa Aswa Aswa Aswa Aswa Aswa Aswa Aswa KalereE gaugrng pt gauging pl Andre$/s potnt Muconda cfl Mparo A Kyemutuzr cross Kyamutuzr cross Tourists' pornt Tounsls' pornl Tounsts'pornt Tounsts'point East Cutlne beiow culline MuzEi c{ Tnbutarv of Aswa 04.03 24 03 24 03 04 03 10 03 10.03 1 '1.03 10.03 1 't .03 14.03 25.03 14 03 05 03 05 03l in n,lt 48 72 68 1 1 12 04 38 60 27 50 16 ,16 l ?i 12l| 1 3 9 1 0 9 36 31 27 9 39 16 12 6 0 17 69 59 0 1 1 ,tE 7 33 18 11 0 1 1 12 1 3 11 0 0 3 0 60 6 0 201 144 194 18 n 0 0 0 0 0 2 1 11 43 2 0 't6 211 ol 0 'l 1 1 0 20 71 49 46 r2] 2l 281 341 rl ;l 56 32 I 35 36 23 21 55 .t8 18 13 40 22 36 23 21 55 ,t8 18 4a 3 .10 22 0 0 0 0 0 0 0 0 0 0 0 0 0 0t ol 23 rl3 1'l Table 4 Checkpoints for the monltoring of Simulium neavei breeding sites in the northern onchocerciasls focus after suspension of river treatments (cf. map Flg. 6 for locatlons of checkpoints) ') including time needed for trapping and examination of crabs Fig. 1 Onchocerciasis foci in Kabarole district ,l3oo30.E a J'lt"ii'ltr .;ttttaaat' .ti ... . . .. Boundary of oncfiocerciasis focus O lOkm ,-{ Z ATR E A Northem focus B Southem Focr.rs te&r Alb..t ,cN -Vrv @ Ei3 ,i t:. i . \--.. : t h. i. Qcotgo lbradrl titI II I t t I t Lako--' Etlw.rd tI a f a a a a t t t , att I aI ,t , Fig. 2 Breeding siles ol simulium neayei in the northem onchocerciasis focus of Kabarole district before vector control (1994) - Breeding of S. neavei O Catching site {r----"-' O I 2 3 I lXal+t--+, @d--- AO t III ( t t I -_)( ) t crturr J ,l II II I , I a "ody:J t{ t I (er, I tI II !..!reruao:t _-.\--i -.-.--r'-- \ Fig 3lnfections(%ofparousfemales)withLl/L2ofonchocercavolvulusinsimuliumneavaifuomKiiuradam(catchingsiteB), when community based ivemectin treatrnents otthe human population were carried out Kijura and Katende (1991-1994). 60 6 8 10 12 .E +o ra- o :, 9so G CL ta- o s20 10 lvermectin treatments I =KUura =Kabende 8 10 12 2 4 6 8 Months V1.1991 to Xtt.{994 46 o Fig.4 Numberof s imulium neavei caught per day (1994 to 1996) at catching sites Busasa, Kijura damand sogohi bridge (ci Fig.2) before and after the onset ot "o-niior-ni"riLlri. in June 1995. First experimental treatments of the Sogohi river near Sogohi bridge were carried out since August 1994. 120 3 roo g, E80 (E o b60 og40 o c, 20z First treatments of the Sogohi river I Tt-?---VVII IXXI I Months January 1994 to December 1996 4- Busasa -a- Kijura Sogohi YVV Catching site: -.? IX I Il---t- -i- Ii- I I -T- I t- I I It_t-T IT-| -.- -i\I\ I Tlr \\ \-....- \ _\\ -\\ Y\ ,ttttt I Fig.S Dosing points used to eradicate S. neayel from the northern onchocerciasis focus fl-able 2) O Catching site A Dosing point 'ft ss-' 34j ft -r"/d;-.,-. Y;,-{--'-::,J a' "rrr,r::".,, 10, (e., -_*^rIalgx+ I t € 4Ezt -0 ft::"'".'j----'^--)\-.- Sp I '*r,tJ^tG (et, -- --.{llo_IS.. I A J 9)6\ z,l A f) Fig. 6 Proposed checkpoints for monitoring s. neavei breding sites after suspension of river treatments g checkPoint (cf' Table 4) O Catching site .lrl z\) O 1 2 3 ( 5Knf-+r Nl I I1su ru-212t \tI I I II I I ;f-Klerutozt _-.\---{\1 '-----' ''ZoD--'.-. 14 t0c I( I I II \ I I I t ? 13 d' .<o)'- @7- 4 l\- 5