Vector-borne disease implications and theircontrolby Brian KaySadly, decisions to develop large-scale waterresources are usually based on economic andpolitical rationales. Considerations of healthhave often received only cursory attention. Theauthor details the problems of vector-bornediseases and provides selected case histories fortheir control.

Bulinus truncatus, the snail that transmits schistosomiasis or biharzias,lives in shallow stream-beds or irrigation ditches.

WHEN A STREAM is dammed,the new lake presents differentecological conditions in terms ofshoreline availability, water flow,thermal stratification, oxygen levelsand respiratory demands. Followingan initial burst of activity to utilizethe organic matter in drownedvegetation and flooded soil, itwould be expected that planktonpopulations will develop. Pop-ulations of mosquitoes, blackflies,molluscs, zooplankton, crustaceansand fish become plentiful when suchconditions prevail. It will be shownthat many of these are implicatedin the transmission of pathogens tothe developing human community.

Fluctuations in water levelscaused by initial flooding, seasonalchanges, or as part of watermanagement policy cause dramaticeffects to both terrestrial andaquatic flora and fauna inhabitingthe peripheral zone. In the tropics,however, new terrestrial pasturesmay be established to provideextensive food and shelter for manyanimals during the dropping water-level period, which may last severalmonths. On Lake Kariba, forexample, birds feed on chironomidlarvae stranded by falling waterlevels and these animals, in turn,provide an abundant source ofblood for arbovirus vectors such asmosquitoes.

Downstream from the dam wall,the ecological changes may bediverse, affecting fisheries, soilquality, nutrient levels and aquaticbiota. For example, the spawninggrounds of the bivalve mollusc,Egeria radiata were changed withthe creation of Volta Lake, andother consequences relating to the

Brian Kay is at the Queensland Institute ofMedical Research, Bramston Terrace,Herston, Brisbane, Australia 4006.

Nile dams will be discussed later.

Kainji, NigeriaPrior to 1962, the Government ofNigeria investigated thehydrological and hydro-electricalpotential of the Niger, Benue andKaduna rivers. With financialassistance from UNDP, the Kainjiarea of the Niger river wasinvestigated further, althoughsocia-economic and health issueswere excluded. In 1962, the NigerDams Act was announced, resultingin the Niger Dams Authority, whichwas responsible for administrationof the Act. Although arrangementsfor public health administration had

originally been left out, 12 per centof the total project costs (US$208million), was finally allocated forresettlement. This resulted in44,000 people being rehoused in 141new villages and two towns whichhad reasonable general services,e.g., a water supply was provided.

One year after construction hadstarted in 1965, several consultantsfrom WHOfUNDP were asked tomake recommendations relating tohealth and socio-economicdevelopment. The FederalGovernment of Nigeria acted onthese recommendations whichresulted in the FAOfWHO KainjiLake Research Project from 1966-1974, and thereafter, the KainjiLake Research Institute.

The health status prior toconstruction, as in other parts ofnorthern Nigeria, was characterizedby high infant mortality, endemicmalaria transmitted by Anophelesgambiae and A. funestus, andendemic areas of onchocerciasisalong the rivers. Sleeping sicknesshad been brought under control buttsetse flies were still common. Itwas also presumed that the snails

WATERLINES VOL.9 NO.2 OCTOBER 1990 3

Bulinus globosus and B. pfeifferiwere intermediate hosts ofschistosoma haematobium and S.mansoni respectively, but trans-mission probably occurred at lowlevels.

Prior to construction, snailvectors of schistosomiasis werefound to be abundant throughoutthe valleys of the Niger and someof its tributaries and also in theconstruction camp area. Notsurprisingly, the occurrence of thesesnails suggested that schistosomiasismight become a problem in thefuture, introduced by the migrantlabour force.

Along the Niger river andtributaries, onchocerciasiseffectively prevented localsettlement and full utilization of thenatural resources. Since 1962, larvalcontrol of both Simulium andAnopheles larvae was instituted toprotect workers from riverblindness and malaria, respectively.DDT at concentrations of 0.33-2.0ppm were introduced into theriver for thirty minutes every tendays. These applications were donemanually in the construction areaand for ten miles downstream in thecatchment of the Oli river. Becausethese treatments gave onlytemporary relief, this expenditurewas ongomg.

On the flooding of the impoundedarea of 1250km2, a number ofknown blackfly breeding sites weresubmerged, and water turbidity andthe steep shoreline undoubtedlyreduced snail breeding. Since thecolonization of the shoreline bysnails, mainly Bulinus globusus, wasinfluenced by weeds andvegetation, only the flat eastern sideof the lake provided the necessarymoist and shady conditions. Thusonly five to ten per cent of themarginal length harboured snailsand, as such, schistosomiasis waslimited to localized areas ofinfection. In 1970, however, 31 percent of the 1,656 residents of fourmajor villages were infected, mainlywith Schistosoma haematobium, butalso with S. mansoni. The majorsites of infection were identifiableeither as being flat or of intensehuman activity around a ferry jetty.These areas were targeted formollusciciding and health educationprogrammes to alleviate theproblem.

Periodic seasonal floodingbetween August to October andDecember to February, and a dryseason which sometimes reducedthe dam to one-third of its capacity,

also had health implications.Reduced water-levels caused weedsand vegetation to dry out, thusreducing the areas of suitablesummer refuge for snails. Duringthe wet season the water becameturbid, which was also detrimentalto the snails.

Frequent adjustments to waterflow over the spillway effectivelyeliminated onchocerciasis for 16kmdownstream along the Niger river.Consequently, more than seventyvillages or fishing camps wereestablished in an area whichpreviously contained no more thanten. In general, however, the effectson downstream populations werefar reaching. The damming of theNiger river seriously reduced theseasonal harvests of downstreamfarmers by terminating annualflooding, and the livelihood of over20,000 Nupe families was affectedas the annual income from fishingand grain production decreased by50-70 per cent. This reductionextended over hundreds ofkilometres to the apex of the Nigerdelta.

Only marginal improvementswere created in health care. Theaccessibility of the two, and laterthree, hospitals remained poor, andthe dispensaries continued to serveas the major health care providers,hampered by problems ofinadequate support andinaccessibility because of the lackof passable roads. Mobile clinicswere first introduced in 1974 fromNew Bussa, and later on, followinga survey in 1979 which establishedthat 60 per cent of the villagers hadnot received any health careservices, the introduction ofprimary health workers in thevillages was proposed. Thelarviciding of Simulium infestedstreams in a 50km radius around thedam site constituted the onlyplanned intervention for vectorcontrol.

Despite the fact that theresettlement operation at Kainjiwas reasonably successful, and thata large investment in healthimprovement and vector control($600 per person) for this purposewas made, there were fewadvances. Greater consideration insiting the new villages could havealleviated the schistosomiasis and,in some cases, the onchocerciasisproblems. Malaria mortality couldhave been considerably reduced bya balanced network of basic healthservices. The general healthsituation could have been improved

Coming in theJanuary issue

A Water DecadeRoundup

Waterlines provide ome foodfor thought about where to gofrom here.

Welcome CARE Canadaand AMREF

From thi i ue onward ARCanada will b nding 300Waterlines ub cription to itcountry offices and fieldworker •and AMREF will bending 50.pon or d by CID and wi

Development o-op rati nre pectively thi type of upp rtfor Waterlil/ en ure that aUfobjecti e i further d - bygetting information to the p piewho can u e it.

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through the prOVISion of betterwater supply and sanitation toreduce gastroenteritis, guinea worminfection, and intestinal helminthinfection; improved housing toreduce infections and epidemicmeningitis; and enhanced roadcommunications to improve theaccessibility of health care.

The Nile dams, EgyptFrom 1953-1954, an internationalgroup of experts examined theviability of the Aswan project todam the Nile river for irrigation andpower production. Theconsequences of restrictingconsiderations to technical andeconomic aspects, thus neglectingenvironmental issues, were farreaching. Following six years ofnegotiations between Egypt andSudan, the engineering work began,along with preparations for theresettlement of some 110,000Nubians living in an impoundedarea of 65,000km2.

The Aswan project, costing $625million, created Lake Nasser,extending some 900km from thetown of Aswan to the confluenceof the Blue and White Nile. It wasdesigned to convert an almostrainless zone in the Nubian desertinto arable land (506,000ha) and toincrease the productivity of rice andsummer maize growing areastotalling over one million hectares.Along with other benefits, it was

4 WATERLINES VOL.9 NO.2 OcrOBER 1990

Checking a remote stretch of river for larvae living in the fast-flowing water.

expected that the national incomeof Egypt would increase by morethan ten per cent or approximately$470 million per year. That is, 75per cent of the costs would berecovered every year, an extremelyprofitable investment by any terms.

Drastic reductions in the amountof silt carried into the Nile delta hadbroad ramifications, however,including the increased salinity ofthe subsoil water, the loss ofapproximately 14,500 tonnes ofcalcium nitrate which was depositedas natural fertilizer on floodedlands, and the loss of the sardinefishing industry, which supported150,000 people and was worth $7million. The disappearance of thesardines from Egyptian shores wasattributed to the lack of flood-bornenutrients and the changes in watersalinity. In order to offset erosionproblems along the Nile, additionalirrigation and power dams wereconstructed between Aswan andCairo with a further $100 million.

On the positive side, by 1975Lake Nasser was yielding 2,000tonnes of fish per year and hadattracted a substantial fishingcommunity, mostly from UpperEgypt. But most of the fishermenlived on board their boats and werecarriers of urinary schistosomiasis.By defecating and urinating into thewaters, the fishermen introduced asource of infection into the lake.

By 1971, aquatic weeds andplants such as Potamogetonpectinatus had become establishedand provided a suitable habitat forBulinus truncatus snails in at leastthree areas on the western shoresof the lake. Because of increasedhuman contact with water,Schistosoma haematobium (urinaryschistosomiasis) prevalence rose byten-fold giving infection rates of 100per cent in some communities. Theecological conditions for the spreadof intestinal schistosomiasis alsobecame more suitable with thestabilization of the waters. Snailsof the genus Biomphalariacolonized the northern areas of thescheme and the incidence ofSchistosoma mansoni also increasedto high levels.

The Nile area has experiencedprofound ecological changes inmodern times because of a seriesof water-resource projects carriedout since 1925 when the Gezira-Managil Scheme began. Followingthe creation of Lake Nasser, theRahad Scheme began in 1975 andas a consequence, conditions havebecome more suitable for the

breeding of the indigenous malariavector, Anopheles pharoensis, butmore importantly it has allowed thenorthward expansion of one ofAfrica's worst malaria vectors,Anopheles arabiensis. During 1941-2, this mosquito caused the deathof 130,000 people in Upper Egypt,and in 1950, A. arabiensis reachedAbu Simbel. In both of these cases,A. arabiensis was eradicated in thenewly invaded areas.

In 1967 it was estimated that anadditional 2.65 million people inEgypt would become victims ofschistosomiasis, resulting in aneconomic loss of $560 million peryear. In the Blue Nile HealthProject alone, more than $1.2million per year was spent onmolluscicides to control the snailhosts of schistosomiasis. Withrespect to malaria control, indoorresidual spraying and larvicidingwere required to depresstransmission. On the Blue Nile,malaria prevalence in children waslow, 0.4 to 4 per cent, butwidespread insecticide resistance ofA. arabiensis is forcing changes inthe control strategy. Should vectorcontrol through insecticide use fail,the negative economicconsequences of the Nile projectswill become even more obvious.

Kamburu, KenyaKamburu is one of four dams on theTana river of central Kenya,designed for the power generation

of 350MW as well as for irrigation.Although no budget provision wasmade originally, $50,000 becameavailable for multidisciplinaryecological and health surveys in1974 and 1977. Experts from WHO,FAO, UNDP and the World Bankhad deplored the absence orinaccessibility of such data.

This case history demonstratesthat it is possible to document thehealth effects of dams throughmodest means. The guidelines forepidemiological studies concen-trated on schistosomiasis, malariaand onchocerciasis, with attentionbeing paid to vector snailpopulations in the inundated areaand upstream. The effect of the damon local food supplies and water-borne enteric disease nutrition werealso considered. Demographic andepidemiological surveys wereconducted with the Kamba people,some living on the lakeside andothers 4 to llkm inland as a controlgroup for comparison. Blood wascollected by fingerprick; simpletests were done to determineanaemia and to diagnose malaria.Stool and urine samples were takenfor diagnosis of schistosomiasis anddetermination of albumin levels.Those with enlarged spleens ofgrade three or higher receivedsplenic punctures for diagnosis ofvisceral leishmaniasis. Bloodplasma was also available forserological studies to determine therange of previous infections.Migration was monitored as an

WATERLINES VOL.9 NO.2 OCTOBER 1990 5

indication of habitat desirability.The Quetelet index (a height toweight statistic) was used to indicatenutritional status; and property andcattle holdings and number ofpeople residing per house was usedto indicate socioeconomic status;and sickness, immunization status,overall crude birth and death rates,and lakeside contact were alsorecorded.

In relation to health, lakesideresidents were worse off than thoseinland. They suffered fromincapacity an average of two tothree days per fourteen. Althoughlakeside people were betternourished than inland residents in1974, by 1977 this advantage hadlargely disappeared; iron deficiencyand a haemolytic factor related tospleen enlargement contributed toa local anaemia problem. It wasthought that much of this was dueto malaria and other parasiticinfections. The colonization of themargins of Kamburu lake by themajor malaria vector, Anophelesgambiae was probably responsiblefor the increased malariaparasitaemias of 7.5 per cent in 1974to 33.9 per cent in 1977.

Three surveys of snail prevalencefrom 1974-6 indicated that althoughBiomphalaria pfeifferi, B.africanus, Bu/inus globosus and B.nasutus occurred upstream, theywere poorly established in the lakedue to the slow establishment ofsuitable plants. Surprisingly,Bulinus truncatus, a vector ofurinary schistosomiasis, was foundbreeding in the lake. Because theprevalence of Schistosoma mansoniinfection was six to eight timesgreater in the lakeside residentsthan in those from the inlandvillages, it has been concluded thatthe lake could easily become a focusof infection once the higher plantswere established.

Cukorova Plain, TurkeyMalaria has long been endemic inTurkey, but prior to the 1950s therewas a dearth of statistical data evenwith respect to parasite prevalence.By 1957, the national malariaeradication programme, employingindoor residual spraying of DDT,was started and was reported tocover a population of 30 million.The annual parasite incidence(API) per 100,000 was reported as126 in 1957-58 and by the early1970s, the API had been reducedto almost three per 100,000 withonly 49 cases in the Adana area.

Eradication and control serviceswere then considerably reduced, tothe point where they were unableto detect in time or deal with a crisiswhich occurred in 1977.

In the mid-1970s an extensiveirrigation project was started insouthern Turkey which resulted ina large increase in irrigated land inthe Cukorova Plain, including theimmediate area around Adana. Therapid increase in agricultural andindustrial development in this areacaused a substantial migration fromthe eastern areas of Turkey to thesouth-west, first on a seasonal basis,and then permanently.

In 1977, the dispersal of thespecialized surveillance teams andthe failure to detect and respond intime to an increase in cases amongthe migrants and the indigenousinhabitants in the Adana area,culminated in a serious epidemic ofmalaria. Anopheles sacharovipopulations had increased vastly asa result of the irrigationprogramme. In 1977, some 115,000cases were reported and the APIrose to 278 cases per 100,000. Theproblem was further compoundedby the development in A. sacharovipopulations of resistance toorganochlorine insecticides. Whenmalathion was introduced as areplacement, inhabitants in theinfected area refused to acceptcontinued sprayings due to theodour of the insecticide. Variousspray measures reduced the API to67 per 100,000 and resulted in areduction of malaria to 29,234 casesin 1979. Refusal rates increasedfurther, however, and during 1982and 1983 respectively, 18,537 of62,038 and 35,919 of 66,681 malariacases in Turkey were diagnosedfrom the Adana area.

The irrigation system, startingfrom small collector dams,consisted of large irrigation canals,over 15m wide with concretebottoms and sides, whichdistributed huge quantities of waterto major localities. The majorproblem, however, was caused bythe numerous irregular run-offditches used to drain off excessirrigation water.

Although the IrrIgationauthorities were slow to accept thatinadequate drainage was the majorproblem, some 3.6 million m3 ofdischarge channels are now clearedannually to ensure that they remainunsuitable for A. sacharovibreeding. The average income offarmers in the area has increasedthree to five times but at the

expense of a resurgence ofPlasmodium vivax. Although thepoor social acceptance of indoorresidual spraying and thewidespread insecticide resistance ofA. sacharovi has helped tocompound this problem, there isno doubt that the provision ofdrainage channels would haveprevented most transmission.

Future ProspectsThe case histories demonstrate thatlack of foresight with respect tohealth issues consideration at theplanning stage can lead to economicunderachievement and considerablehuman distress. The diverseecological ramifications of theKainji and Nile dams suggest thatmultidisciplinary advice is needed.The failure to design adequatedrainage facilities in the CukorovaPlains scheme is surprising in viewof the care taken with the irrigationcanals. The massive outbreak ofmalaria was totally predictable inview of the reduction in nationalsurveillance.

Despite considerable outlays forhealth and related services (albeitas an afterthought), Kainji has notbeen as successful as it could havebeen. Health workers andconsultants were never given theopportunity to engage inpreventative medicine (the mostcost-effective type) but were forcedinto the continuing curative mode.Although the situation at Kamburuwas similar, this case studydemonstrates an approach whichprovides effective guidelines at lowcost. The importance of theincorporation of such studies at theplanning stage cannot beoveremphasized.

These case studies show thepositive value of sound planningand management in relation tocomplex environmental changes iswell-documented and the need touse them in a positive way isessential.

ACKNOWLEDGEMENTSI wish to thank my PEEM colleagues, andA,M,A. Imevbore and I.M,V. Oomen forhelpful discussions and permission tosynthesize their data on Kainji andKamburu. I am particularly indebted toN.G. Gratz, I. Najera and D. Muir, WHOGeneva, for freely making available datafrom unpublished reports and to R. Slooffand R. Bos for commenting on thismanuscript.

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