Journal of the American Mosquito Control Association, 18(3):202-206' 2002Copyright A 2OOZ by the American Mosquito Control Association, Inc.

LOW INSECTICIDE DEPOSIT RATES DETECTED DURING ROUTINEINDOOR RESIDUAL SPRAYING FOR MALARIA VECTOR CONTROL

IN TWO DISTRICTS OF GOKWE, ZIMBABWE

HIERONYMO T, MASENDU,I NOZIPHO NZIRAMASANGA, ITIO CHARLES MUCHECHEMERA,

ABSTRACT. Questions have been raised about the quality of indoor residual spraying for malaria vector

control after the decentralization of the national malaria control program in Zimbabwe. Given the critical

role this control method plays, we conducted an exercise to determine the amount of insecticide (mg activeingredient/m, of lambda-cyhalothrin) applied during routine house spraying. Severe insecticide underdosingwas detected. Spraying efficiency ranged between 63.4 and 76.17o on walls, and 52.7 and 63.2Vo on roofs.Differences between 2 districts suggested the problem originates from deficient training and lack of pumpcalibration. Underdosing can undermine effective residual insecticide activity and the expected reductionin d isease t ransmission.

KEY WORDS Indoor residual spraying, malaria vector control, insecticide deposit

INTRODUCTION

Indoor residual spraying of insecticides plays acentral role in malaria control programs in Zimbab-we and several other countries in southern Africa.A reduction in malaria transmission is expected af-ter effective residual spraying operations (Schliess-mann 1983). Several insecticides are available forindoor spraying, but some of these have becomeineffective because of the emergence of resistance,whereas others, although effective, are not accept-able because of their high mammalian toxicity orhazardous persistence in the environment. Insecti-cide effect is dependent on proper application,which in turn is affected by various fbctors such asthe equipment used and the individual skills of thespray persons. For each insecticide, standard de-posits are recommended for sprayed surfaces ortreated fabrics following extensive collaborativeevaluations involving research institutions, indus-try, and the World Health Organization (WHO1971, Wright l97l). The target deposit rate is nor-mally expressed in grams or milligrams of activeingredient (AI) per surface area. Of concern is theobservation during postspray evaluation with con-tact bioassay tests that the residual effect of insec-ticides is not always certain on surfaces, especiallyon mud-plastered walls (Masendu et al. 1998). A1-though variation in deposit rate is inevitable, themagnitude of this variation during routine indoorhouse spraying under operational conditions has notbeen fully quantified. We conducted a study to col-lect empirical data on the insecticide deposit rateswith the goal of recommending measures to im-prove chemical application during routine indoorresidual house spraying in Zimbabwe.

I Blair Research Institute, Ministry of Health and ChildWelfare, PO Box CY 573, Causeway, Harare, Zimbabwe.

'�Special Analysis Laboratory, Department of Researchand Specialist Services, Chemistry and Soil Research In-

stitute, Ministry of Agriculture, PO Box CY 550, Cause-way, Zimbabwe.

MATERIALS AND METHODS

A qualitative analysis of residual house sprayingfor malaria vector control was conducted in GokweNorth and South districts in December 1999. The ob-jective was to determine the insecticide deposits onhut surfaces during routine indoor spraying. Filter pa-pers were pinned on wall and inner roof surfaces be-fore spraying as previously described by Gratz andDawson (1963). Major sprayable surfaces in a typicalhut consist of mud-plastered walls and a grass-thatched roof (Fig. l). The sprayers were asked tospray as normally regardless of the presence of filterpapers. Filter papers were removed 30 min afterspraying after allowing them to dry. The filter paperswere packed and labeled according to the hut andsprayed surface. Each sprayer was provided with aform to record details about the pump, chemical, andspraying process. Filter papers were forwarded toBlair Research Laboratory for documentation of theaccompanying data, and finally to the Special Anal-ysis Laboratory of the Chemistry and Soil ResearchInstitute of the Ministry of Agriculture for insecticideresidue analysis.

Assessment of spray teams, equipment, andchemicals: Information on the organization of thespray teams, pumps, chemicals used, and sprayingoperations was collected during the time of spray-ing.

Method of sampling,: The team leader randomlyidentified huts for inclusion in the trials. Filter pa-pers were randomly pinned onto walls and roofs ofeach hut before spraying. In each hut, 4 filter paperswere placed on the walls and 4 were placed on theinside of the roof. We used Whatman No. I filterpaper (Whatman International, Maidstone, Eng-land) of 12.5 cm diameter.

Residue analysis: Lambda-cyhalothrin depositswere analyzed by using the gas liquid chromatog-raphy (GLC) technique described in the manual ofthe Natural Resources Institute (1995). The amountof insecticide on each filter paper was determinedfrom the whole filter paper, with a surface area of

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JouRNAL or rss AvInntc.qN MosQuno CoNrnol AssocrerroN Vor . 18 . No.3

0$122769 m2. The lst step involved extraction ofthe pesticide by using the surface rinse procedure.Each filter paper was soaked in 100 ml of hexaneovernight. The extract was decanted, evaporateddown, and then made up to 25 ml with hexane be-fore GLC analysis. The efficiency of recovery of

this method exceeds 957o.In the 2nd step, the di-luted sample was analyzed on a Varian 3400 GLCinstrument fitted with an electron capture detector(ECD). The ECD is extremely sensitive to com-pounds containing chlorine and will detect nano-gram quantities. The column (200 cm X 2-mm in-temal diameter; Varian Inc., Walnut Creek, CA)was packed with l.5Vo OV-17 (Varian) + l.95%oOV-210 (Varian) on CWHP 80/100 (Varian). Theoperating temperatures were 235oC for the column,245"C for the injector, and 300'C for the detector.Nitrogen was the carrier gas with a flow rate of 30ml/min. The detection limit of the GLC was 0.01ng. The GLC peaks of the test material were com-pared to those of reference lambda-cyhalothrin(>98.77o purity). A stock solution of l0O ng/pl wasprepared by dissolving 0.0101 g in 100 ml of hex-ane, and a working solution of 0.1 ng/pl was used.A solvent blank (hexane) was run for each lot ofsamples and in between injections on the GLC.

Statistical analysis: An average of 4 wall and 4roof filter papers per hut collected from 22 hutswere analyzed. The /-test was applied to determinethe similarities between observed and expected de-posits on the wall and roof surfaces.

RESULTS

Spraying teams and equipment

Two types of spray pumps, the Hudson (H. D.Hudson Manufacturing, Chicago, IL) and the Glo-ria l72R (Hochleistungs-Spruhgerat, Gloria-Werke,Wadersloh, Germany), were in use in the 2 districts.An inventory of pumps available conducted in theGokwe North camp showed that the Gloria to Hud-son ratio was 6: l. In response to a questionnaireadministered among the sprayers, 11 Gloria and 4Hudson pumps were in use, indicating the predom-inance of the Gloria pump. Seven sprayers did notindicate the type of pump they were using. Gen-erally, the pumps seemed to be in good condition;the Hudson pumps in Gokwe North had code marksindicating year of manufacture ranging from 1992to 1995. The year of manufacture could not be de-termined for the Gloria pumps. Pumps did not havelance extensions or constant pressure-regulating fa-cilities. Nozzle material was indicated as eithersteel (n : 8) or brass (n : 9), whereas the remain-der was not specified (n : 5). Various flat fan noz-zles (Spraying Systems Company, Wheaton, IL)were in use, including from Teejet 8002-E (n: 5),8004 (n -- 3), 9OO2 (n : 3), and 9003 (n : r).

Nozzle type could not be determined on somepumps. Some of the common problems associated

with the pumps included damaged rubber hose andplungers, blockages, and even loss of nozzles andfaulty pressure gauges.

Sprayers were provided with basic protective

clothing, namely overalls and masks, except theywere not provided with goggles. Sprayers did not

have stretcher beds or mattresses to sleep on incamp while on tour of duty. Soap was provided forlaundry and bathing. Experienced staff trained theteams with support from the private sector a weekbefore deployment. The Gokwe North group con-sisted of 38 sprayers, including 2 camp guards, Isupervisor, I driver, and 5 team leaders, making up2 teams each with a team leader and a deputy. Ide-ally, the team should have a warner (who alertscommunities about the spraying exercise in ad-vance) and a pump minder in addition to 15 spray-ers. Ten insecticide charges were issued per personper day and each sprayer was expected to spray 3-5 huts per charge depending on structure size.Teams were deployed early in the morning to takeadvantage of the cooler temperatures given theharsh weather conditions in the area. Remunerationwas US$18 (ZD$950) per person for 23-25 work-ing days per month. While in camp, visitors werediscouraged to reduce intemrption of day-to-dayactivities, and for general security reasons.

Spraying procedure

Insecticide charges were prepared by mixing62.5 g of lambda-cyhalothrin (Icon@; Zeneca, Fern-hurst, Surrey, England) 10 WP with lO liters ofwater for Hudson or Gloria pumps. Because Iconis supplied in water-soluble sachets, the mixing isdone directly in the pump rather than in a bucket.The resulting mixture is an aqueous suspensioncontaining O.O6257o of the active ingredient. Thevolurne per surface area that sprayers were trainedto apply could not be determined. The recommend-ed target deposit of lambda-cyhalothrin is 30 mgAVm'� with the acceptable range of 25-3O mg AVm2. Spraying at 4O mVm2 is calculated to result ina deposit of 25 mg/rrP, whereas spraying at 48 mUm2 would result in a deposit of 3O mg/m'� withoutrunoff.

Insecticide deposits

Average lambda-cyhalothrin deposit rates onwalls and roofs surfaces were both less than theacceptable minimum of 25 mg/m2 (Table 1). Con-siderable variation occurred in insecticide deposits,which ranged from 0.35 to 89.37 mglm2. The av-erage insecticide deposit on the roofs was lowerthan on the walls, but this difference was not sig-nificant (1 : 109; dt = 164; P = O.28).

After analysis of variance (F : 58.8, P : 0.0O1,df : 1), the data from the 2 districts were analyzedseparately. Gokwe North had more acceptable in-

secticide deposits, whereas Gokwe South figures in-

SnprrMsnn 2002 INsEcrIcrDE Deposn RATE rN Mer-enre CoNrnol 205

Table l. Insecticide deposit rates (on filter papers) grouped to indicate categories of acceptable, underdosing, andoverdosing with respect to a target of 30 mg active ingredient (AI)/mr.

Percent (Vo) of filter papers in different insecticidedeposit rate categories (sample size in parentheses),

Locality

xDeposit

Hut sur- (mg AI/m,)face (n)'

<18.75mg/m2

t8.75-25mg/m2

25-30mg/m2

30-36.2 >36.25mg/mz mg/m2

Gokwe South

Gokwe North

Overall

9.9 (40)5.3 (39)

27.1 (4s)2s.6 (42)19 (85)15 .8 (81 )

8s (34)e4.8 (37)37.7 (17)47.6 (2O)60 (51)7O.4 (s7)

12.s (s)2.6 (r)

3s.5 (16)14.3 (6)24.7 (21)8.6 (7)

2.s (r)2.s (r)

13.3 (6 )l l . 9 ( s )8.2 (7)7.4 (6)

WallRoofWallRoofWallRoof

0 00 0

2.2 ( r ) l l . l (s)9.s (4) 16.6 (7)1.2 ( l ) 5 .9 (s)4.9 (4) 8.6 (7)

rt = mean; n : smple size (number of filter papers analyzed).2 Insecticide deposit rates of 18.75 and 36.25 mg/m2 represent arbitrary cutoff values equivalent to 25Eo below the acceptable minimum

of 25 mg/m2 md 2OVo above the acceptable maximum of 30 mg/m,.

dicated serious underdosing. When compared withthe target dose of 3O mg/m2, the deposits for GokweNorth were not significantly different for both walls(P < 2.O2, t : O.78, n : 45 at 95Vo confidencelimit) and roofs (P < 2.O2, t : 1.61, n : 42 at95%oconfidence limit). In contrast, the values for GokweSouth were significantly lower than the target forboth walls (P > 2.O4, t : 18.4, n = 4O at 95Voconfidence limit) and roofs (P < 2.02, t = 26.27,n : 39 at 95Vo confidence limit). The greatest pro-portion of the samples had insecticide deposits low-er than 18.7 mg/rn2, reflecting serious underdosing.This was more evident in Gokwe South, where 857oor more of the filter paper deposits were below 18.7mg/m'� (Table l). Small proportions of the sampleamounting to 2.57o in Gokwe South and 13.37o inGokwe North had insecticide deposits falling with-in the acceptable range of 25-3O mg AVm'�. Onlylimited overdosing was recorded and this was confined to samples from Gokwe North. In addition tobeing wasteful, excessive insecticide can have a re-pellent effect on the targeted endophilic Anophelesarabiensis Patton by preventing this vector mos-quito from resting on treated surfaces.

Efficiency of the spraying technique

Taking 25 and 3O mg/m2 as acceptable minimumand maximum target deposit rates, respectively, theefficiency of spraying on the walls and roofs rangedfrom 63.4 to 76.17o and 52.7 to 63.27o, respective-ly. The overall spraying efficiency for the whole hutranged from 58.1 to 69.68Vo.

The lower limit of 2O mg AVm2 recommendedfor lambda-cyhalothrin in the range 2O-3O mg AUm2 (Chavasse and Yap 1997) is considered too littlefor the sorptive soils that constitute the relativelycoarse and porous mud plastering used in most ru-ral homes in Zimbabwe. The Vector Control Sub-committee of the National Malaria Control Programrecommends a deposit rate of 30 mg AVm2 whenIcon lO WP is used. The rationale is that high de-posit rates would counteract rapid insecticide loss

due to porous mud surfaces (Bami 1961, Gerolt1 9 6 1 ) .

We did not determine insecticide falling on thefloor, which results from bounce-off. Insecticidefalling on the floor has several implications, rang-ing from wastage, potential beneficial impact onother household pests, and unintentional insecticidepoisoning of house occupants, especially childrenwho play and sleep on the floor. Falling spray de-posits may also increase the exposure to insecticideand poisoning of the sprayers during the spraying,especially of those with inadequate protective wear(Durham 1963). Lambda-cyhalothrin was reportedto cause itching, especially when sprayers cookedon an open fire. Characteristic of all alpha-cyanopyrethroids, lambda-cyhalothrin is known to causeskin and throat irritations, as reported here. Icon l0WP was the only insecticide used in the assessedareas, which reflects the central insecticide procure-ment process at national level. Chemical content in 3randomly sampled sachets that were analyzed rangedfrom 9.4 to lo.l%o lambda-cyhalothrin, thereby rulingout possible faulty chemical supplies.

DISCUSSION

Underdosing of insecticide clearly occurred onboth wall and roof surfaces during routine spraying.Although obtaining a uniform application rate is ac-knowledged to be impossible, deviation from themean should remain within acceptable limits. In-dications are that the low insecticide deposits are aproblem related to the skills of the spray persons.The problem of underdosing apparently was relatedto application technique, possibly due to sprayingat too fast a rhythm. That training was the likelyproblem is supported by the different performancesobserved between the 2 districts. Sprayer fatigueresulting from the workload also could be a con-tributing factor because spraying an estimated 40huts per day may be asking too much from I spray-er. Rushed spraying may ensue to achieve these tar-gets, resulting in the underdosing such as reported

206 JounN,qr- or rse AuBmceN MosQuno CoNrnor- Assocr,qloN Vor-. 18, No. 3

here. That deposits on the roof were found to belower than on the wall probably stems from the lackof face protection; sprayers risk getting insecticidein their eyes if they look toward the roof duringspraying (WHO 1986). Provision of pump lance ex-tensions would improve reach and thus aid insec-ticide application in high conical roofs, which tendto receive less than the desired rates. Frequent ag-itation of the pump is necessary to prevent insec-ticide sedimentation after the initial mixing. Pilfer-ing of chemical by sprayers may result in theover-dilution of remaining charges to compensateand thus ostensibly achieve the expected coverage.Chemical pilfering is probably linked to the smallremuneration package, which often is paid after theperformance of work. The sample size was notlarge enough to assess the effect of pump and noz-zle variation on insecticide application. One directimplication of these disturbing observations on vec-tor control is that effective impact on disease trans-mission cannot be expected under such a situation.Insecticide rates below target may eventually en-hance the development of insecticide resistance, asituation that would have far reaching consequenc-es on disease prevention and control.

Recommendations

Calibration of pumps to suit the particular insec-ticide in use at all times is urgently needed. Sprayertraining should be reviewed and assessed regularlyto ensure adherence to specific technical require-ments. Supervision of sprayers and spray teamsshould be reinforced to ensure the proper prepara-tion of charges and application of insecticide. Re-duction of the number of structures sprayed by anindividual per day may be necessary to increaseefficiency. Adequate protective gear should be pro-vided for the sprayers and its correct use should beencouraged.

ACKNOWLEDGMENTS

We are grateful to the Midlands Provincial Med-ical Director, District Medical Officer, field spray

teams in Gokwe North and Gokwe South, and the

Director and staff of Blair Research Institute for

their support in this study. We are indebted to S.

Siziya for his input on statistical analysis of the

data. Special thanks are due to M. Coetzee for re-

viewing the manuscript. Reference lambda-cyhal-

othrin was kindly provided by Zeneca Zirnbabwe(Pvt.) Ltd. This work was supported in part by a

grant from MIM/IVHO/TDR (ID 990078) and the

Ministry of Health and Child Welfare. We would

like to thank the Secretary for Health and Child

Welfare for permission to publish this manuscript.

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