Similium neavei vector elimination activities in Itwara focus, Kabarole district, western Uganda: annual NOTF secretariat technical report to Technical Consultative Committee (TCC), February 2007

JI ! olL 7 SIMIJLIITM NEAVEI VECTOR ELIMINATION ACTIVITIES IN ITWARA FOCUS, KABAROLE DISTRICT, WESTERN UGANDA. OzuGINAL:English ANNUAL NOTF SBCRETARIAT TECHNICAL REPORT TO TECHNICAL CONSULTATIVE COMMITTEE (TCC) To APOC Management by 31 Januarv for March TCC rneeting AFRICAN PROGRAMME FOR ONCHOCERCTASTS CONTROL (A 5 (- e_51cc Bitl ch\ cb? Attg EW Yo I ;,t i'^3 \ A COUNTRY/: UGANDA UGANDA Approval vearz 200(i Reportins Period (Month/Year): FEBRUARY 2007 Project vear of this report: (circle) I 2 3 4 t3 t4 6 7 8 9 t0tttz Date submitted: 14'h February 2007 1;1 rofu) ?ANNUAL NOTF SECRETARIAT TECHNICAL REPORT TO TECHNICAL CONSULTATIVE COMMITTEE (TCC) ENDORSEMENT Please confirm you have read this report by signing in the appropriate space. OFFICERS to sign the report: Country : UGANDA National Coordinator Natne: Dr. R. Nd yenyi. Signature Date: l4'r' Februuy 2007 NOTF Chair Narne Signature Date: This report has been prepared by Narne: Mr. T.L. Lakwo Designation. Senior Entornologist td,,;'Signature: .. Date: l4'l'Fe 2007 WII(YAPOC. Ircbrualr 2007 ,ACRONYMS APOC - African Programme for Onchocerctasis Control ATP - Annual Transmission Potential TCC - Technical Consultative Committee CDTI - Community Drrected Treatment with lvermectin GfZ - German Technical Cooperation WHO - World Health Organization WHO/APOC. Fcbman 2(X)7 TABLE OF CONTENTS FOLLOW UP ON TCC RECOMMENDATIONS.... 3 EXECUTIVE SU M MARY.................. 4 SECTION 1: BACKGROUND INFORMATION 6 1 .1 Geography and socioeconomic background ...... . .. 6 1.2The vector . ......7 1.3 Background to the current report. ..........7 SECTION 2: VECTOR ELIMINATION IMPLEMENTATION IN THE FOCUS.....8 2. 1 Aquatic survey for S. neavei immature stages ........ B 2.2 Adullfly catches at establrshed sites. .. ......... B 2 3 lntegrated data analysis B 2.4 Overview of vector elimination activities in the focus ."....8 SECTION 3: RESULTS 3. 1 Aquatic survey for S. neavei immature stages ... 3.2 Adult fly catches at established sites 3.3 lntegrated data analysis Overview of vector elimination activities in the focus SECTION 4: DISCUSSION 4.1 Recommendations of TCC 23 4.2 Aqualic surveys and adult catches 9 '..'.,9 . ..10 .. 10 ....12 ....13 .. 13 .,,.14 Conclusions 15 SECTION 5: ACHIEVEM ENTS, STRENGTHS, OPPORTUNITIES, ETC.......... 1 5 5.1 Achievements ....15 5 2 Strengths . ..... 15 5.3 Opportunities ... .. 16 S4Challenges . .16 5.5 Recommendations....... ....... 16 Acknowledgements .... ......16 References ...... ... ..... 17 2 WHO/APOC. Februan'2007 FOLLOW UP ON TCC RECOMMENDATIONS TCC session: 23 held on 11'15 September 2006 Numher of Recommendation in the Report 7'CC RECOMMENDAT'ION ACI'IONS TAKEN BY THE NOTF SECRETARUT FOR T-CC/APOC MGT USE ONLY Trt'o The cessation of sun'eillance in lltc ttutu.t locus Survcillance activities in thc main focus rrerc conductcd sir ttmcs during thc pcriod under rev'ieu (Jan. Feb. Apr. Mar'& Ar-rg 2(X)6) but ceascd on rcccipt ofTCC 23 rccommendations. An additional round of catches and crab trapping in the sub-foci of Siisa and Asu a. on the basis of the 2006 budget alrcadr allocated br APoc Management. [n case lan'ae of the,\1 nelvet are drscor cred. localizcd lanrcrding rnust irrunediatelr be undertaken. Adult flr' catches in the established sites in the tu'o sub-foci and crab trappings ucre marntained durrng the pcrrod under reviel No immature stages (larvae) \\'ere encollllter to \\arrant anr larviciding opcrattot-ts 3 WHO/APOC. Februan 2(X)7 I EXECUTIVE SUMMARY Itwara focus is located around the ltwara forest reserve about 25 km northeast of Fort Portal, the headquarters of Kabarole district. lt traverses the districts of Kabarole and Kyenjojo districts approximately covering 600 Km2.The focus was hyper endemic of onchocerciasis with S. neavei s.s. as vector breeding in Sogohi, Siisa and Aswa river systems. Population at risk is about 76,000, representing 10o/o of the total population of the districts. The purpose of this project rs to eliminate onchocerciasis vector from this isolated focus so as to achieve permanent interruption of transmission. A project to eliminate the vector using the larvicide temephos was initiated by GTZ in I 995 By the end of 1995 S neaveis.s had already disappeared in ltwara main focus. Since 1998 monitoring through the support of African Programme for Onchocerciasis Control (APOC) has been ongoing in this focus mainly by crab collection and examination, and adult fly catches at established catching sites. The monitoring activities conducted during the period under review revealed that out of the 817 crabs caught from 11 key checkpoints in ltwara main focus, were all negative for Simultum neavei immature stages. ln Siisa and Aswa sub-foci 1,358 and 3,838 crabs were caught respectively, and all were negative for immature stages of S. neavei. At the three operational catching sites, no adult S. neaveiwas caught An overview of crab trapping and examrnation revealed that from 1998 to 2006 over 51,000 crabs were caught. From these evidences, it can be assumed that transmission has completely ceased in ltwara main focus since now more than 9 years and the vector have been eliminated. With a vector free status for over 9 years and ivermectin treatments for now more than 14 years, onchocerciasis should be on a rapid decline. The project main strengths had been the availability of very experience staffs in both Kyenjojo and Kabarole districts coupled wrth support from the respective districts. lt is therefore proposed that routine surveillance in the two sub-foci be scaled down to six times a year in 2007, four times in 2008 and twice a yeat in 2009 It is anticipated the districts would rntegrate surveillance activities of once a year from 2010 onwards. 4 WHO/APOC. Fcbman 2007 The APOC Management should put in consideration a plan for the certification of elimination of S. neavei vector in this focus once surveillance activities cease. 5 WHO/APOC. Fcbman'2007 SECTION 1: BACKGROUND INFORMATION 1.1 Geography and socioeconomic background There is now one active foci of Onchocerciasrs in Kabarole district situated to the northern part bordering Kibale district and part of the same focus straddles into Kyenjojo district. Simulium neavei s.s. used to be the only vector tn this focus before the plan to control the vector began in 1995. Prior this, control was only based on the community based distributron of ivermectin that started in the second half of 1991 lVost of the northern focus is located around the ltwara forest reserve about 25 km northeast of the district capital of Fort Portal. The reserve covers 87 Km2 of steeply undulating terrain and is bordered to the west, south and east by large tea estates, which are highly important economtcally. To the north it is bordered by subsistence farms with some large cattle ranches along lower Sogohi and ltluzizi rivers. The atea is densely populated and onchocerciasis used to be highly endemic And at the time of initiating control about 80% of the population of 45,000 living around the ltwara Forest Reserve was estrmated to be rnfected with Onchocerca volvulus. The situation according to some recent survey revealed that the epidemiology of the disease has drastically changed for the better (Ndyomugyenyi et a|,2002). The ltwara focus is not completely isolated from the two secondary foci on the Siisa river system and the Aswa River to the east. The Siisa river area is mainly of a savanna type with subsistence farming and large cattle ranch reaching the ltluzizi River to the north. There is little forest left along the streams due to ongoing deforestation and it is surprising that S. neavei used to survive in this area. [Vlost of the Aswa River passes through forest or borders forest reserves to the east. lts lower section is in deep forest (lVluhangi Forest Reserve). 6 WHO/APOC. Fcbruan 2(X)7 1.2The vector Simulium neaveis. sfr. was the only vector of O. volvulus in the focus. lt belongs to the S. neavei group of species (Subgenus Lewisellum), which develop in an obligate phoretic association wrth river crabs. The crab Potamonautes atoysiisabaudiae is the phoretic host of S.neavei in the focus that covers part of Kabarole and Kyenjojo districts. 1.3 Background to the current report A project to eliminate the vector using the larvicide temephos was initiated by GTZin 1995 By the end of 1995 S. neaveis s had already disappeared in ltwara main focus. However, when GTZ phased its financial support to this project, the African Programme for Onchocerciasis Control (APOC) came in as a main partner to complete the elimination activities. At that time there was still some slight infestation in the sub-foci of Siisa and Aswa. There was however, a delay in eliminating the vector from these sub-foci due to insecurity at the time and the drscovery of a pocket of breeding on R. lVlusabira and R. N/ukonda. Localized river treatments and monitoring were conducted in these sub-foci under the APOC support from 1998 up to date. The present report reviews monrtoring activities that were conducted on monthly basis in ltwara main focus and the two sub-foci during the course of 2006. An overview of elimination activities from 1998 to 2006 is also presented, discussed and appropriate recommendations made. 7 WHO/APOC. Februan 2(X)7 SECTION 2: VECTOR ELIMINATION IMPLEMENTATION IN THE FOCUS 2.1 Aquatic survey for S. neavei immature stages Surveillance through crab collection and examination were conducted at 11 key checkpoints in ltwara main focus during the period under review. tMost of the monitoring efforts focused on the two secondary foci of Aswa and Siisa. River crabs were caught using a local metal designed funnel shaped basket traps baited with meat (Raybould, 1969) which was left in the river/stream for about an hour or overnight then examined for crabs carrying larvae and pupae of S. neavei. This is one of the methods used to monitor the level of infestation. The rnformation was entered in designed crab forms and summarized on monthly basis. 2.2 Adult fly catches at established sites. Full day (07:00 to '18:00) fly catches on human bait were carried out usually eight times a month by locally recruited vector collectors at the three established catching sites of Siisa, Andrew's, Tourist (D, E, F; Fig.1) in the two sub-foci. Numbers of flies caught were recorded on hourly basis. 2.3 lntegrated data analysis ln July 2006 the APOC lVlanagement sent lVlr. Ake Assi, an expert in the control of Simulium vectors to conduct an integrated data analysis for ltwara focus. Thrs was to help assess the impact of the two rnterventions (ivermectin and vector elimination) on the magnitude of onchocerciasis in this focus. Part of lVr. Ake's mission in Uganda will be highlighted in this report. 2.4 Ovewiew of vector elimination activities in the focus A summary of the trend of crab collectron and examrnation in ltwara marn focus and the two sub-foci of Siisa and Aswa was compiled since 1998 when APOC started to support monitoring activities in this focus. 8 WHO/APOC. Fcbman 2007 SECTION 3: RESULTS 3.1 Aquatic survey for S. neaveiimmature stages The results of crab collection and examinations from key check points in ltwara main focus and the two secondary foci of Siisa and Aswa is shown in Table 1. ln Itwara main focus, a total of 817 crabs were caught from 12 key checkpoints and all were negative for S. neavei immature stages. ln Siisa sub-focus, from the 9 checkpoints sampled, 1,358 crabs were caught and all were negative. Similarly, in Aswa sub-focus out of the 3,838 crabs caught from twelve checkpoints were all-free of S. neavei immature stages. Table 1: Crab collection and examination in ltwara focus, Kabarole district, western Uganda: 2006 Month ltwara main focus Aswa sub-focus Siisa sub-focus 2006 Number of crabs Number of crabs Number of crabs Caught Positive %+ve Caught Positive %+ve Caught Positive %+ve Jan Feb Apr N/lay Jun. Jul Aug Nov. Dec. 00 0.0 0.0 0.0 0.0 0.0 433 253 306 381 82 845 645 672 221 00 00 00 00 0.0 00 0.0 0.0 0.0 178 215 42 146 11 186 277 303 0 00 0.0 00 00 0.0 00 00 00 96 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 120 0 99 303 113 86 Total 817 0 0.0 3,838 0 0.0 1,358 0 0.0 oo' percentdge. -\'e = posltlve 9 WHO/APOC. Fcbman' 2(X)7 3.2 Adult fly catches at established sites The results of adult fly collections at the three established catching sites are shown in Table 2. There has been no adult S. neaveicaught in any of the three sites (D, E, F, Fig: 1) during the period under review; an indicatron of transmission interruption. Table 2: Adult S. neaveicatches at the three sites in Siisa and Aswa sub- foci, Kabarole district, Western Uganda. Month (2006) Catching sites January February [/arch April lVay June July August September October November December Siisa 0 0 0 0 0 0 0 0 0 0 U 0 Tourist 0 0 0 0 0 0 0 0 0 0 0 0 Andrew's 0 0 0 0 0 0 0 0 0 0 0 0 Total 3.3 lntegrated data analysis The integrated data analysrs was to include epidemiological rnformation on ivermectin treatment and some aspects of the vector. During the period when APOC N/lanagement started supporting surveillance activities, field dissections of 000 l0 WHO/APOC. Fcbman 2(X)7 adult S. neavei had stopped so relevant data that could be used to calculate some entomological indices like Annual Transmission Potential (ATP) was not available at the time Nilr. Ake visited. The data on fly catches were partly available as the bulk of it entered in Epi lnfo 6 was lost when the computer hard disk crashed. However, when [\4r. Ake installed a new user friendly excel programme, all data for adult catches from 1998 to date were entered. A copy of this data was sent to [Vlr. Ake in October 2006 for his further analysis and the report on the same to be communicated to the APOC management. But regards ivermectin treatment in this focus, it was observed that therapeutic coverage varied between 620/o lo 83% and Geographical coverage had been maintained around 100o/o from 1998 to 2005 (Fig. 1a,b; Ake, et.a|,2006)). ITWARA FOCUS FlG. 1a: KABALORE ANO KYENJOO: COMPARISON OF THERAPEUTICAL COVERAGE TRENO AND TOTAL POPULATION TREATED Total Poo 120 000 rcpspnl2tr6nlreated lTherrp"r@t"or"rigJ 11.uoo 100 000 80 000 60 000 40 000 20 000 0 97 98 99 2000 2001 2002 2003 2004 2005 FlG. 1b :KABALORE AND KYENJoJO:TRENO OF THERAPEUTICAL AND GEOGRAPHICAL COVERAGE b"dt[ o""i;X;". @ Geographical coverage +Therapeutical coverage 80% 70Yo 60% 50% 40o/o 30% 200/o 10% 0o/o 97 98 99 2000 2001 2002 2003 2004 2005 1000/o 80% 60% 40Yo 20% 0Yo 80% 70% 60% 50To 4Qfo 30o/o 20o/o 10% 0% ll WHO/APOC. Februan'2007 Overview of vector elimination activities in the focus lVlonthly surveillance involving crab collection and examination generated a substantial amount of data that has all along been useful in assessing the vector free status of the entire focus. The numbers of crabs, which were examined from 1998 to December 2006 and add up to more than 51,000, are summarized in Table 3. For ltwara main focus where the vector first disappeared, the vector free status has now been observed for over 9 years. The table further shows how the infestation rates in the river systems declined and when the sub-foci were probably vector free. lt further indicates that the Aswa and [\4ukonda/Nlusabira systems that delayed the elimination process are now vector free for at least over 3 years. Of the 8,304 and 4840 crabs caught in Aswa and Nlukonda/lVlusabira systems since 2004, respectively, all were negative for S. neavd immature stages. Table 3: Overuiew of the numbers of river crabs Potamonautes aloysiisabaudiae examined from 1998 to 2006 and percentages of crabs carrying immature stages ol Simulium neavei. Sub focus ltwara Siisa Aswa Tota! Rivers Sogohi system Siisa system Aswa Muko +Musab Year No. crabs o/o tve No. crabs o/o tve No. crabs % +ve No. crabs o/o *ve 1 998 1 999 2000 2001 2002 2003 2004 2005 2006 634 662 594 1 094 1149 343 1974 2146 817 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 993 1 383 1 488 841 1461 2118 2096 1302 1 358 0.4 01 0.1 0.1 0.3 0.0 0.0 00 0.0 541 1114 300s 2290 1440 34s4 3823 2228 2333 18.0 3.1 1.0 04 0.1 0.1 0.0 0.0 0.0 n.d 90 627 1441 1 364 2305 2393 1012 1 505 n,d 00 24.7 02 26.3 0.1 0.0 00 0.0 2168 3249 5714 5666 5414 8220 1 0286 6688 3838 Total 9,413 13,040 20228 10737 51243 Muko = Mukonda river; Musab = Musabira river; n.d = no data; +ve = positive 12 WHO/APOC. Fcbruan 2(X)7 .r t | | SECTION 4: DISCUSSION 4.1 Recommendations of TCC 23 N4onitoring activities continued in the two secondary foci of Aswa and Siisa as recommended by TCC 23 However, before the receipt of these recommendations, some surveillance actrvrties had already been conducted in Itwara main focus and the data still further confirmed the vector free status of the rrver systems. This surveillance that was conducted 6 times within the period under review was to further confirm the vector free status since catches at the established catching sites were suspended. However, the general trend of the results from these surveillance activities highly confirms the possibility of this vector species (S. neavei, s.s.) having been eliminated from this focus. lt rs proposed therefore that routine surveillance activities be scaled down to six times a yeil n 2007, four times in 2008 and twice a yeat in 2009. This gradual scale down is expected to monitor the status of the two sub-foci of Siisa and Aswa since the vector free status has only been observed for more than 3 years. lt would further allow the district to integrate these activities in their work plans. Similarly, the ltwara main focus where the vector has disappeared for now 9 years should be checked every 2 years and the districts should also sustain this. Professor Garms last assessment recommended cessation of activities in the whole focus (Garms, 2OO5). With one additional year of surveillance actrvities in the focus, the findings still conformed to Professor Garms's recommendations. The APOC Management should put in consideration procedures for certification of elimination after the 3 years of surveillance activities in the focus. lt may not be very wise to abruptly cease surveillance activities but there wrll be gradual scaling down to a level where it will be sustained by the districts For that matter it is hoped that the activities will be integrated into the district health plan 13 WHO/APOC. Febman' 2(X)7 'l 4.2 Aquatic surveys and adult catches. The results of aquatic surveys gave very strong evidence of vector elimination since no immature stages of S. neavei were detected in the several crabs caught. There was no sign of re-colonization of the ltwara focus, where river treatments were suspended at the end of 1996. The Nyakibuguta, which was heavily breeding before treatments, is now vector free since more than 9 years. There was no measurable transmission of onchocerciasis any more in this sub- focus since more than 9 years. However, in the eastern sub-foci of Siisa and Aswa elimination was slightly delayed due to some pockets of breeding that was detected in 2002. lt can be assumed that transmission has been interrupted because since 2004 over 13,000 and 4,000 crabs caught in Aswa and Siisa systems, respectively were found free of S. neavei immature stages. The three vector collectors who have been based in these sub-foci since 2003 never caught a single S. neavei. We can now confidently say that transmission of onchocerciasis has ceased in the whole of the northern focus. The result that none of the more than 17,000 crabs caught and examined during the last two years (last positive crab with 1 larva found in the lVukondwa on 14 April 2003) was positrve provides evrdence that the vector has disappeared (Table 3). However, it has to be noted that it is not possible to prove that the vector is extinct, or exists at low level below threshold at which it is detectable by our monitoring methods But given the fact that surveillance has been conducted for all these periods and no risk of re- infestation had been detected, it is high time future plan for certification of elimination is considered as surveillance activities are scaled down to a level where the districts can sustain it. This would give more time for the field team to concentrate in other foci where control/elimination is planned. 14 WHO/APOC. Febman 2007 ia Conclusions There was no sign of S. neavei in ltwara main focus according to the available data lt can be assumed that transmission has completely ceased there since now more than 9 years and the vector have been eliminated. With a vector free status for over 9 years and ivermectin treatments for more than 14 years, onchocerciasis should be on a rapid decline. The eastern sub-foci now also maintain a vector free status and no positive crab has been encountered for the last three years; it can be assumed that onchocerciasis transmission along Siisa and Aswa river systems seems to have been practically interrupted. lt is therefore proposed that routine surveillance activities in the two sub-foci be scaled down to six times a year in 2007, four times in 2008 and twice a year in 2009. SECTION 5: ACHIEVEMENTS, STRENGTHS, OPPORTUNITIES, ETC. 5.1 Achievements . The S.neaveivector free status has been maintained for nine years in the Itwara main focus. . The vector free status has also been observed in Siisa and Aswa sub-foci for now over 3 years. . No adult S.neaveiwas caught in the three existing monitoring sites during the period under review. 5.2 Strengths . The availability of trained, experience and committed field staff based in Kabarole and Kyenjojo districts . Availability of well established laboratory equipped with the necessary field equipment/gears. . Support from the respective District Health offices in the monitoring activities. 15 WHO/APOC" Fcbruan' 2(X)7 5.3 Opportunities . lntegrated district work plan. This wrll allow post-elrmination surveillance to be integrated in the district work plan 5.4 Challenges . Sustaining the post-elimination surveillance in the focus by the two districts. 5.5 Recommendations ln view of the vector free status observed in the two sub-foci of Siisa and Aswa, it is proposed the routine surveillance activities be scaled down to six times a yeat in 2007 , four times in 2008 and twice a year in 2009. The districts (Kabarole and Kyenjojo) should integrate surveillance activities in their work plans from 2009 onwards. Adult fly catches in the three established sites in the two sub-foci should be scaled down from B days/month to 4 days/month. The S. damnosum species being caught in Aswa sub-focus need to be identified to establish their vector status. o o o o 16 WHO/APOC. Februan 2007 \.ll Acknowledgements We thank the African Programme for Onchocerciasis Control (APOC) for their continuous financial support that enabled monitoring activities to be conducted in this focus We are grateful to the Kabarole and Kyenjojo districts field-based Vector Control officers particularly lVlessrs. E. Tukesiga and J. Katamanywa for their interest and commitment in all aspects of the monitoring activities. We are also indebted to Professor R. Garms and the GTZ Team Leader, [Vlr. Tom Rubaale for their keen interest in this focus and for the financial and logistical support that assisted in the various aspects of monitoring. The work would have been impossible without the untiring cooperation of the entomological assistants and the vector collectors. We also thank the office of District Health officers of Kabarole and Kyenjojo for their support in terms of logistics during the field operations. 17 WHO/APOC. Februan 2(X)7 \ ') a References Ndyomugenyi R., Tukesiga, E., Buttner, D.W., & Garms, R. (2004). The impact of ivermectin alone and when in parallel with Simulium neavei elimination on onchocerciasis in Uganda. Tropical A/ledicine and lnternational Health, 9:882- 886. Raybould, J N. (1969). Studies on the immature stages of the Simulium neavei Roubaud complex and their associated crabs in Eastern Usambaras in Tanzania. lnvestigations in rivers and larger streams. Annals Tropical lttledicine and Parasitology, 63'. 269-287 Garms, R. (2005). Vector control and vector elimination in onchocerciasis foci in districts of Kabarole, Kyenjojo and Kamwenge in western Uganda. Assessment February/[Vlarch 2005. Report to GTZ Basic Health Services. Ake, A., Lakwo, T., Ndyomugyenyi, R. (2006). lntegrated analysis of vector control and CDTI data from N/lpamba-Nkusi focus from 1999-2005. Report to APOC N/lanagement (Unpublished document). 18 WHO/APOC. Febman 2007 r t, I l t\o -o(\ a r=) o o I lJ- t BF lz UJ oz IJ lIJ E,;f to 'z o tr t<z = uJ IFa o o. t o]L z J o-Yt o = x uJzz l I t 1 i L a L o)o Eo oL+lci oO L o ol o _o' C .9 ,9, L o o-l U) i- o lf tt-oo(\ El[]r 1 lr 1 6 o o o Ba o o o .9. @ .E pxl cl L o E o i tLFoz -o c .9atL o o_ =la" E o o- o- fa o 6' 't o x x X o Xz x x X X x 1 x I - x f l o, -c'o G o1 E P fD a_ x x x xi -r l| x X =lrL I I x I -ofa o 3a E C N(, ,g U) .E a x L] lllx il IIf l 'iix x I *- r li r-f1 Al I @ l i I l -) i l hrJI .td Nortltttrtt rtttt;ltclcerciasis focus' Siisa and Aswa river ..;ystcttu;. nrro*t inOicate location of dosing points' o Catching sites D Siisa' E'F Aswa Fig.2: 1 o(J 20 N o 2 E, \ \ 012 3 4 Skm 4 e .f' 1 , ( |\ I 5 \\ o Siisa 23 \ 26 e ! 34 ( tt) 1 \ I I\ l. oyoro 22 :a a Aswa \ -) F + I I <- ,I E t\\ ,I I I I t r)\) -r1\2J 1 rusozl 3 I 13[Kra t\ 0 f --l Katoko t ( \)I 35 t