Trials with Aerosol Spray to Control Aedes aegypti-Biting during DF/DHF Epidemic By
M.A. Ansari Malaria Research Centre, Indian Council of Medical Research, 20 Madhuban, Delhi-110092 (INDIA)
Abstract Hexit Mos kit aerosol application @ 16 ml per 10 seconds sprayed in rooms against Aedes aegypti at 0700 hrs prevented 95.8±4.2% vector to land on human volunteers for 9.65±1.3 hours. Spraying also prevented 87.9±4.1% Aedes aegypti to enter sprayed rooms for 8.25±0.7 hours. Hexit Mos kit aerosol can be used by communities for protection of infants and other vulnerable groups staying at home against Aedes bites.
Introduction During the 1996 outbreak of DF/DHF in Delhi(1), among the control strategies suggested, stress was laid on the need to promote equity among communities through sharing of responsibilities and selfreliance. To this end, control strategies which are simple, non-toxic and can be handled by people themselves assume greater significance and people need to be empowered with knowledge and skill. To achieve these objectives, commonlyavailable commercial aerosol as a tool for personal protection against mosquitoes was evaluated with encouraging results. For protection against bites of Aedes aegypti, Hexit Mos kit aerosol was evaluated and the results are incorporated in this paper.
Material and methods A commercial product Hexit Mos kit aerosol was used in this study. Aerosol comprises 0.02% ww deltamethrin, 0.133% ww allethrin as active ingredient, and 99.85% ww other ingredients. Aerosol was released @ 16 ml in 10 seconds in rooms of about 3.5x3.5x3.5 m. at 0700 hrs before the forenoon biting peak. Cylindrical cages (12 cm long and 80 cm diameter) made of 20 mesh galvanized wire screen were used in the study to expose mosquitoes. Batches of laboratory- reared ten Aedes aegypti females were exposed at an interval of one hour after aerosol application. A control was held without exposure to the aerosol. Mortality was recorded by holding
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exposed adults in the same cage for 24 hours in the laboratory at 28oC±2oC and 80% RH. Field experiments were conducted in Sadiq Nagar - a residential colony in south Delhi where Aedes indices were predetermined and estimated as 16.75 MHD and 8.81 Container Index. Field observations on landing of mosquitoes after aerosol release were made from 7 a.m. to 6 p.m. in October 1996. During this period the mean temperature varied from 22.2- 26.1oC and relative humidity ranged from 57 to 66%.
the other at late afternoon. Aerosols can be used as a supplementary method to ward off Aedes mosquitoes and thus ensure protection of vulnerable groups, i.e. infants and women staying at home, from acquiring dengue infection. Table 1: Field evaluation of Hexit Mos Kit aerosol against Aedes aegypti (7a.m. - 6 p.m.) Repli -cate E 1 4 3 2 2 3 1 2 2 2 2 3 4 2 3 2 4 3 2 4 4 Entered in Rooms C 25 25 25 25 19 19 19 19 18 18 18 18 26 26 26 26 24 24 24 24 %P 84.0 88.0 92.0 92.0 84.2 94.7 89.4 89.4 88.8 88.8 83.3 77.7 92.3 88.4 92.3 84.6 87.5 91.6 88.3 83.3 PT 8 7 9 8 8 8 7 8 8 8 7 7 8 7 10 7 8 9 7 8 E 0 0 0 0 2 1 1 1 0 1 0 0 1 0 1 0 0 2 1 0 Landed on human volunteers C 9 9 9 9 18 18 18 16 16 16 13 13 13 13 15 15 15 15 9 9 %P 100.0 100.0 100.0 100.0 88.8 94.4 94.4 93.7 100.0 93.7 100.0 100.0 92.3 100.0 93.3 100.0 100.0 86.6 88.8 100.0 PT 11 11 11 11 9 9 10 8 11 10 11 11 8 11 9 11 11 7 8 11
Results and discussion Fig. 1 gives the results of Hexit Mos kit spray on the mortality of Aedes aegypti caged in cylindrical wire meshes. The results revealed 100% knock down of mosquitoes for three hours, i.e. three successive batches of Aedes aegypti exposed for one hour died. Thereafter, there was a decline in the mortality up to 6 hours. Corrected mortality after 24 hours is given in Fig.1. Table 1 and Fig 2 give the results of field evaluations. It was revealed that one release of aerosol spraying @ 16 ml in 10 seconds prevented the entry of Aedes aegypti into the rooms, i.e. 87.9±4.1 mosquitoes were prevented from entry for a period of 12 hours. As a direct consequence of this, the landing rate of Aedes aegypti was reduced by 95.8±4.2. Aedes aegypti is a domestic mosquito and predominantly bites during daytime with two peaks, one before forenoon and
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 E C P PT
Experimental Control Protection Protection time
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Figure 1. Percentage knockdown and corrected mortality after holding females in cyclindrical cage kept in Hexit Mos Kit sprayed rooms
Figure 2. Landings/Entries of Aedes aegypti on human volunteers/room in Hexit Mos Kit sprayed and unsprayed rooms
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Acknowledgment Thanks are due to Agrevo Hoechst India Ltd. for ex-gratia samples of Hexit Mos kit. The author is also thankful to Mr N.L. Kalra, Consultant, MRC, for critically going through the manuscript.
References 1. Sharma VP. Dengue Epidemic. Current Science, 1996, 72(4):230 2. Ansari MA and Razdan RK. Evaluation of aerosols against mosquitoes. Proc. Interl. Symp. on Vector-Borne Diseases, 1994, 141-145.
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