Tanzania Health Research Bulletin Health User's Trust Fund (HRUTF) ISSN: 0856-6496 Vol. 8, Num. 3, 2006, pp. 145-148

Tanzania Health Research Bulletin, Vol. 8, No. 3, 2006 pp. 145-148

Evaluation of the bio-efficacy of three brands of repellents against wild populations of anthropophilic mosquitoes

S.M. MAGESA^1* and M.L. KAMUGISHA²

¹Amani Medical Research Centre, P.O. Box 81, Muheza, Tanzania
²Tanga Medical Research Centre, P.O. Box 5004, Tanga, Tanzania

Correspondence: Dr. Stephen Magesa; E-mail: smagesa@nimr.or.tz

Code Number: rb06027

Abstract: Three commercial repellents marketed in Tanzania: Zero Bite^® (a blend of microcrystalline waxes, mineral oils, natural flavours, Olibanum oil, Eucalyptus oil, Geranium oil, Citronella oil and Isopropyl myristrate); X-pel^® (a petroleum jelly formulation containing diethyl toluamide (DEET) and dimethyl phthalate); No Bite^® (a spray formulation with diethyl toluamide, 2 methyl 2,4 pentondiol and pthalic ester acids) were tested and compared for their repellency effect against wild anthropophilic mosquito populations. Human forearms, feet and legs were treated with the repellent products. All repellents provided protection against wild populations of biting mosquitoes (mainly Culex quinquefasciatus and Aedes scatophagoides) with varying levels of efficacy. No Bite^® provided the best overall protection (98%) followed by X-pel^® (87%). Zero Bite^® gave the least protection (48%) against the two mosquito species. All products except No Bite^® displayed reduced efficacy after four hours of application. The results indicate that the two best products give satisfactory levels of personal protection against biting mosquitoes at least for the first five hours, following application, thus could provide complementary protection against mosquito bites particularly during the period when most people have not retired to bed where they may be protected by treated bednets.

Key words: mosquito bites, repellent, bio-efficacy, Tanzania

Introduction

The World Health Organization is currently advocating for integrated vector management (IVM) as a strategy for controlling malaria in endemic areas. The fundamental characteristics of IVM includes the use of methods based on knowledge of factors influencing local vector biology, disease transmission and morbidity, as well as use of a range of interventions, often in combination and synergistically (WHO 2004). Insecticide-treated nets (ITNs) are being promoted as a useful tool against malaria in Tanzania (Magesa et al., 2005). However, individuals would still be exposed to mosquito bites before retiring to bed where ITNs provide protection. The bites experienced before going to bed could be enough to inoculate malaria parasites, raising the need for complementary means for protecting people against early-biting malaria vectors as well as nuisance biting mosquitoes. Repellents would therefore be useful in closing this gap. The use of repellents formulated for the purpose of controlling disease vectors and nuisance biting mosquitoes is getting increasing preference, particularly at the household level (Lines, 1996).

Currently, there are an increasing number of antimosquito measures backed with aggressive commercial marketing claiming that, certain brands of repellents may provide reliable protection against a wide range of biting mosquitoes. Although the efficacy of diethyl toluamide (DEET) has been tested in Kenya (Walker et al., 1996) and Tanzania (Curtis et al., 1987); and p-methane 3,8-diol, an eucalyptus based repellent tested in Tanzania (Trigg, 1996) very few other repellent types have been scientifically tested in Tanzania.

Insecticide screening tests such as the one reported here serve to safeguard the interests of the consumers. Standard methods are employed in carrying out the screening by assessing their biological efficacy against pests and vectors. Equally important, information from such tests provides feedback to manufacturers, thus enabling them to improve on their products (WHOPES, 1998).

We report on field studies conducted in Tanga, Tanzania to evaluate the impact of three types of insect repellents on wild populations of Culex quinquefasciatus, Aedes scatophagoides, Mansonia spp and Anopheles gambiae s.l.

Materials and Methods

The experiments were conducted between May and June 2002 in Tanga City in northeast Tanzania. Zero Bite^® is a blend of microcrystalline waxes, mineral oils, natural flavours, Olibanum oil, Eucalyptus oil, Geranium oil, Citronella oil and Isopropyl myristrate (Shelys Pharmaceuticals, Dar es Salaam Tanzania). X-pel^® is a petroleum jelly formulation containing diethyl toluamide and dimethyl phthalate (Mansoor Daya Chemicals, Dar es Salaam, Tanzania). No Bite^® is spray formulation containing DEET, 2 methyl 2,4 pentondiol and pthalic ester acid Mansoor Daya Chemicals, Dar es Salaam, Tanzania).

Experimental design and test procedure

A 4 x 4 Latin square design was used with hourly catches made to record any short-term residual effect. The design has proved effective as a standardized and repeatable test for comparing several protective measures with each other and a control. Eight experienced male collectors (26 – 47 years old) volunteered to participate as subjects for mosquito night-biting collections. All volunteers were kept on proguanil for malaria prophylaxis throughout the study period. The three treatments and a control were compared by having four collection teams working simultaneously by applying the respective repellents and collecting mosquitoes landing on their exposed legs.

Twenty minutes before commencing the collection period, the repellent was applied by smearing thinly all over ankles, feet, legs and forearms of each treated subject, as generally used in practice. Each collector sat on a stool (c. 40 cm above ground) and each pair collected mosquitoes off each other as well as on themselves, for 50 minutes of each hour. Ten minutes per hour were allowed for collating hourly collections and resting. After each night’s collection period, all collectors washed thoroughly with soap before going to bed, so that the treatment effects would not carry over to the next day. Teams and treatments were rotated between four positions 15 metres apart so that all 64 possible combinations of position, team and treatment were tested over 16 nights. The rotation compensated for any positional differences in the number of mosquitoes, personal differences in catching ability and attractiveness to mosquitoes.

Mosquito collection was carried out from 18:00 to 22:00hr. Using flashlights, pooters and the general procedures as described by Curtis et al. (1987) the collectors aspirated all landing mosquitoes that attempted to bite them. From each pair of collectors, from each hourly catch all mosquitoes collected were transferred into a pre-labelled cup with gauze top. Cups were labelled according to collecting team, treatment, position, and hour of collection. Mosquitoes of each category were held in their respective cups with access to glucose solution on a cotton wool pad until the following day when they were killed, counted and identified.

Data analysis

Data was entered into Epi-Info and analysis done with STATA statistical package version 8 (Stata Corp., College Station, TX, USA, 2003). The protective efficacy of each treatment was calculated as percent protection estimated as 100 x (Control – Treatment) / Control; i.e. number of mosquitoes landing on treated subjects relative to the number landing on untreated control subjects (Mehr et al., 1985).

The hourly protective efficacy for five hours was worked out to give an indication of persistence of the repellency effect for each product. To compare between treatments, the geometric mean numbers of mosquitoes collected per treatment was analysed by analysis of variance, adjusting for collection team and position. Tukey procedure was used for pairwise comparison of means between treatment brands. The number of mosquitoes collected per treatment brand was log transformed [ln(X+1)]. Regression Model for a Latin square with fixed blocking (time and team arrangement effects) and treatment effects was used.

Results

A total of 2963 mosquitoes were collected while attempting to bite. The collected mosquitoes were found to belong to Anopheles gambiae s.l. (0.5%), Culex quinquefasciatus (85.9%), Aedes scatophagoides (15.2%), other Anopheles spp (1.0%) and other Culex spp (3.1%). Table 1 shows a comparison of the repellency effect of the three brands using Tukeys multiple comparisons of mean differences of the numbers collected with each treatment.

Tukey’s multiple comparison shows that there was no significant difference between the repellency effect of No Bite^® and X-pel^®. However, each of the three treatment brands showed a significant difference with the control. In addition, comparison between treatment No Bite^® and Zero Bite^® as well as X-pel^® and Zero Bite^® exhibited a significant difference in their repellency effect.

Results from the model with fixed blocking effect (Table 2) showed that No Bite® was more effective in repelling mosquitoes, followed by X-pel®. Zero Bite® displayed the least effect. Overall, the repellents exhibited varying levels of repellence ranging from 48.6% for Zero Bite®; 87% for X-pel® to 98.6% protection for No Bite® (Table 3).

For each repellent, the efficacy for the first hour was compared to that of the second to fifth hour. Results of comparisons between first and fifth hour gave the following results, χ² = 15.2, P< 0.05 for Zero Bite^®; χ² = 25.7, P<0.05 for X-pel^®and χ² = 2.6, P>0.05 for No Bite^® X-pel^® and No Bite^® were shown to exhibit satisfactory protection (> 80%) five hours after application of the products. On the other hand, Zero Bite^® displayed the least protection at 64.6% during the first hour, dropping to 5.21% after five hours.

Discussion

Three commercial repellents were tested and compared for their efficacy against wild populations of anthropophilic mosquitoes. The mosquitoes caught attempting to bite belonged to Anopheles gambiae s.l., Culex quinquefasciatus, Aedes scatophagoides, other Anopheles spp and other Culex spp populations. The first two species are known to be vectors of Wuchereria bancrofti worms that cause lymphatic filariasis. In addition, Anopheles gambiae s.l., is a primary vector for malaria. The other species are more important as nuisance biting species. However, they could be important potential vectors in situations of outbreaks of arboviral infections.

The repellents exhibited varying levels of overall repellence. Our data suggest that Zero Bite^® is comparatively the most inferior of the three repellents tested, exhibiting an unacceptable level of protection. Analysis of data for persistence of the repellence effect showed that X-pel^® and No Bite^® provided satisfactory protection (> 80%) five hours after application of the products. On the other hand, Zero Bite^® displayed the least protection at 64% during the first hour, dropping to 51% after five hours. Whereas there was no decline in the efficacy of No Bite^® over five hours, X-pel^® exhibited a 14.9% decline in repellence over the five hour period.

Results from the current study clearly show that X-pel^® and No Bite^® were effective in repelling mosquitoes. The repellents also exhibited a satisfactory level of repellence even five hours after their application. Questions have been raised over how to deal with exposure to mosquito bites before retiring to bed where insecticide treated nets would provide protection. A major concern have been that, bites experienced before going to bed could be enough to inoculate malaria or other parasites (Curtis et al., 1987), raising the need for complementary means of protecting people against early-biting malaria vectors as well as nuisance biting mosquitoes. The findings in the current study suggest that X-pel^® and No Bite^® repellents could possibly be useful in closing this gap. Therefore, X-pel^® and No Bite^® repellents could possibly be used as complementary tools for protection against vector mosquito bites, consequently making a contribution towards control of vector-borne diseases.

Acknowledgements

The authors would like to express their sincere gratitude to all field staff who were involved in conducting the experiments. The National Institute for Medical Research, Amani Centre Scientific Committee is thanked for giving permission to carry out the study. The Registrar of Pesticides, Tanzania, provided financial support. The Director General, National Institute for Medical Research is thanked for granting permission to publish this paper.

References

• Curtis, C.F., Lines, J.D., Ijumba, J., Callaghan, A., Hill, N. & Karimzad, M.A. (1987) The relative efficacy of repellents against mosquito vectors of disease. Medical and Veterinary Entomology 1, 109–119.
• Lines, J.D. (1996) Mosquito nets and insecticides for net treatment: a discussion of existing and potential distribution systems in Africa. Tropical Medicine and International Health 1, 616–632.
• Magesa, S.M., Lengeler, C., de Savigny, D., Miller, J.E., Njau, R.J.A., Kramer, K., Kitua, A.Y. & Mwita, A. (2005) Creating an “Enabling Environment” for taking Insecticide Treated Nets to National Scale: The Tanzanian Experience. Malaria Journal 4, 34.
• Mehr, Z.A., Rutledge, L.C., Morales, E.L., Meixsall, V.E. & Korte, D.W. (1985) Laboratory evaluation of controlled release insect repellent formulations. Journal of the American Mosquito Control Association 1, 143–147.
• Trigg, J.K. (1996) Evaluation of a eucalyptus-based repellent against Anopheles spp in Tanzania. Journal of American Mosquito Control Association 12, 243-246.
• Walker, T.W., Robert, L.L., Copeland, R.A., Githeko, A.I., Wirtz, R.A., Githure, J.I., & Klein, T.A. (1996) Field evaluation of arthropod repellents DEET and piperidine compound, A13-37220, against Anopheles funestus, and Anopheles arabiensis in Western Kenya. Journal of American Mosquito Control Association 12, 172 – 176.
• WHO (2004) Global Strategic Framework for Integrated Vector Management. World Health Organization, Geneva. WHO/CDS/CPE/PVC/ 2004.10.
• WHOPES (1998) Draft Guideline Specifications for Household Insecticide Products. Mosquito coils; Vapourizing Mats; Liquid Vapourizers; Aerosols. Report of the WHO Informal Consultation, 3–6 February 1998.–World Health Organization Geneva. CTD/ WHOPES/IC/98.3.

Copyright 2006 - Health User's Trust Fund (HRUTF)

The following images related to this document are available:

Photo images