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Evaluation of a Eucalyptus-Based Repellent Against Anopheles Spp. in Tanzania

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Evaluation of a Eucalyptus-Based Repellent Against Anopheles Spp. in Tanzania Joumal of the Ameican Mosquito Control Association, 12(2):243-246' 1996 Copyright O 1996 by the American Mosquito Control Association' Inc. EVALUATION OF A EUCALYPTUS-BASED REPELLENT AGAINST ANOPHELES SPP.IN TANZANIA J. K. TRIGG Department of Medicat Parasitology, London School of Hygiene and Tropical Medicine, Keppel Street, London WCIE 7HT United Kingdom ABSTRACT. A eucalyptus-based insect repellent (PMD) with the principal active ingredient p-men- thane-3,8-diol was evaluated in the field in comparison with deet. In human landing catches in Tanzania, 3 formulations of PMD were tested against Anopheles gambiae and An. funestus. Repellents, applied to the legs and feet at doses chosen as used in practice, gave complete protection from biting for between 6 and 7.75 h, depending upon the formulation type, with no significant difference between PMD and deet in terms of efficacy and duration of protection. INTRODUCTION be somewhat less effective than deet (Schreck and Leonhardt 1991, Collins et al. 1993). Qu- protection Repellents have long been used in wenling is made from the waste distillate after with the main motivation against biting insects, extraction of oil from the lemon eucalyptus plant being avoidance of nuisance. However, through (Eucalyptus maculata citriodon) and the princi- their reduction in man-vector contact, repellents pal active component is p-menthane-3,8-diol in the can also be regarded as important tools (Schreck and Leonhardt 1991). prevention of vector-borne disease. A preliminary laboratory evaluation of a new For travellers to tropical countries, malaria repellent, PMD, similar to quwenling (Trigg and continues to pose a serious health risk; in the Hill 1996), reported this compound to be almost were 1,887 im- United Kingdom in 1994 there as effective as deet against Anopheles gambiae ported malaria, I which resulted in cases of I of Giles and also to be effective against midges, (Anonymous 19941). The rapid spread of death ticks, and the stable fly. The repellent (trade has increased resistance to antimalarial drugs the name Mosi-guard Natural, MASTA, London, importance supplementary preventative mea- of United Kingdom) is produced utilizing lemon sures. The World Health Organization (1995) "all eucalyptus oil itself, via an extraction process travellers should be told currently advises developed at University College, London. The protection from mosquitoes is their that biting active component (SOVo) is principally p-men- first line malaria". The ar- of defence against thane-3,8-diol with additional isopulegol and ci- mory of personal protection includes the use of tronellol and the repellent is formulated as a pat- bed nets, clothing, and repellents. Since suitable ented mixture of isomers of each. 1957, the most commonly used insect repellent In this paper a field comparison of PMD with formulations have methyl contained diethyl ben- deet against 2 Afican malaria vectors, Anoph- zamide (deet), which is effective against a broad eles funestus Giles and An. gambiae is reported. spectrum of insects. There are disadvantages as- sociated with the use of deet, which stem prin- cipally from its activity as a solvent of paints, MATERIALS AND METHODS varnishes, and some plastics and synthetic fab- Study area: A field trial was undertaken in rics. There have also been concerns over the tox- 1995 in village Mkuzi, Tanga Re- icity of deet (Miller 1982, Roland et al. 1985), June the of gion, Tanzania. village has mostly wattle although serious adverse effects are rare (Veltri The larval habitats for et al. 1994, Osimitz and Grothaus 1995). and daub houses and suitable gambiae In the search for effective alternatives to deet An. and An. funestus. Repellents and application: Three formula- there has been much interest in natural plant ex- tions of PMD (5OVo AI), a pump spray, a stick, tracts (Opoku et al. 1986, Curtis et al. 1990). and a gel, were evaluated for efficacy and lon- The eucalyptus-derived repellent quwenling was gevity in comparison with a spray formulation reported to have largely displaced the commer- of deet (5O7o AI, MASTA) against natural pop- cial market for di-methyl phthalate in China ulations of mosquitoes. For each trial, 6 expe- (Curtis et al. 1990), although it was reported to rienced insect collectors participated in human night-biting catches having been offered malaria rAnonymous. 1994. Annual malaria statistics re- prophylaxis and treatment with sulfadoxine pyr- port, 1994. Malaria Reference Laboratory, London imethamine in the event of contracting malaria (unpublished report). infection. On any one day, 2 subjects applied 243 L 244 JounulL oF THE AMERtcaN Mosqurro CoNrnor_ AssocrerroN VoL. 12,No.2 Thble 1. Total number of Anophelesgambiae andAn. funestus collected by individual subjects with repellent-treatedor untreatedskin and protection time until first bite in minutes (pT) oier a 3-d.V pd.d f"r each PMD formulation tested in comparison with deet spray. PMD spray (0.8 gfleg) vs. PMD stick (1.3 g/leg) vs. deet spray (0.8 gneg) deet spray (0.8 g/leg) Control PMD spray Deet spray Control PMD stick Person No. No PT No. PT No No. PT A 35 (3)' 14(2) 347 19(1) 374 32 (3) rr (2) 33s B 68 (1) r7 (2) 359 13 (3) 362 49 (r) rs (2) 323 C 2s (3) s (l) 360 2(2) 372 33 (3) 4 (1) 47O D 26 (2) 0 (l) >540 l r (3) 3ss 36 (2) e (l) 3s7 E 43 (2) r (3) 447 0 (l) >s40 r7 (2) 3 (3) 375 F 2s(r) 5 (3) 360 3 (2) 490 l0 (1) 6 (3) 327 Mean 37.O 7.O >402.2 8.0 >415.5 29.5 8.0 364.5 (6 h, 42 min) (6 h, 55 min) (6 h, 5 min) rThe day on which each test was done is shown in parentheses. deet,2 applied PMD, and 2 remained as untreat- applied at rates of 0.8 g/leg for PMD spray and ed controls. Repellents were applied as evenly deet spray, 2.O g[eg for PMD gel, and 1.3 g1eg as possible to the legs and feet from the knee for PMD stick. The results of the night-biting downwards. It was decided to assess the repel- catches are shown in Table l. Anopheles funes- lents as used in practice and the choice of dos- t r.r was the most common species biting during age was therefore calculated on the basis of what the study (69.3Vo of all mosquitoes collected), the team members considered adequate to give followed by An. gambiae (29.7Vo), and l7o other even and comfortable coverage oftheir legs. The species. When analyzing these data, two likely doses were determined by weighing the contain- sources of background variation were consid- ers before and after repellent application and ered: l) day to day variation in the number of taking the average of all applications. mosquitoes caught by the controls, and 2) vari- Repellent was applied 5 h prior to commenc- ation between persons in attractiveness to mos- ing the night catch after preliminary trials indi- quitoes (Curtis et al. 1987)-a fact apparently cated that both deet and PMD gave at least 5 h illustrated in this data set by person B who was repellency. In the interim period, subjects were consistently a high scorer regardless of treat- careful to keep their clothing away from the treated skin. ment. This was confirmed by a 2-way analysis variance, Test procedure: In a method adopted from of allowing for treatments, which Curtis et al. (1987), subjects sat separately on showed a highly significant between-person benches chairs variation in the number of mosquitoes caught (F or spaced approximately 1O m : apart for a period of 4 h each night from 2200 rO.32,P < 0.001). h until 0200 h. Using flashlights and test tubes To compensate for these factors, the number they caught those mosquitoes that had landed on of bites each day on individuals treated with re- the skin and were clearly probing to feed before pellent were first subtracted from the mean con- transferring them into labelled paper cups to be trol catch on that day. Data were then analyzed counted and identif,ed later. using the nonparametric Wilcoxon signed rank Subjects remained seated in the same position test, pairing the corrected PMD and deet data on 3 consecutive nights for each phase of the for each person. This test was also applied to the trial; treatments were rotated nightly. This meant time until first bite data (i.e.. the time interval that each subject experienced each treatment: a between repellent application and the first bite formulation of PMD, deet, and control; the ro- recorded), again pairing the deet and PMD data tation compensated for any positional differ- for each subject. ences in the number of mosquitoes, and personal The result was a nonsignificant difference be- differences in persistence of repellent, catching tween PMD and deet both in terms of efficacy ability, and/or attractiveness to mosquitoes. (P > 0.05) and longevity (P > 0.05) of repel- lency against total anopheline biting for each of RESULTS AND DISCUSSION the formulations of PMD tested. The procedure outlined in the Materials and At the chosen dose rates, all repellents tested Methods section resulted in the repellents being provided greater than 6 h protection from biting. 245 JuNr 1996 FrELD EvALUATtoN oF A NEw INsEcr REPELLEI'I-I Table l. Extended. PMD stick (1.3 g/leg) vs. deet spray (0.8 g/leg) PMD gel (2.O glleg) vs. deet spray (0.8 g/leg) Deet spray Control PMD gel Deet spray No. PT No. No.
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