Chapter 11
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Olyset® net: a Long lasting Insecticidal Net for Vector Control Takaaki Itoh1, Yoshinori Shono1, John R. Lucas2 and Takao Ishiwatari3 1 Environmental Health Division, Sumitomo Chemical Co., Ltd., Tokyo, Japan 2 Sumitomo Chemical (U.K.) Plc, London, United Kingdom 3 Agricultural Chemicals Research Laboratory, Sumitomo Chemical Co., Ltd., Hyogo, Japan Olyset® net is a long lasting insecticide treated mosquito net (LLIN) manufactured by Sumitomo Chemical Co., Ltd. The net material is polyethylene monofilament fibre, incorporated with permethrin 2% (w/w). Short exposure to Olyset® netting results in bite inhibition activity and rapid knockdown of mosquitoes. Field evaluations have shown that Olyset® net is an effective tool for controlling not only malaria but also dengue fever and leishmaniasis. Olyset® is a registered trademark of Sumitomo Chemical Company Limited.
Introduction Long –lasting insecticidal mosquito nets (LLINs) which retain activity for at least 3 years are recommended for malaria control by the World Health Organization (1). Olyset® net is an LLIN manufactured by Sumitomo Chemical Co. Ltd. The net material is polyethylene monofilament fibre, incorporated with 2% w/w permethrin as the active ingredient (2). Olyset® net was the first LLIN to be submitted to the WHO Pesticides Evaluation Scheme (WHOPES) for evaluation, and the only LLIN currently fully recommended by WHO (3). In this paper we describe the biological efficacy and field evaluation of Olyset® net.
© 2009 American Chemical Society Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
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Contact Effect of Olyset® Net on Mosquitoes We investigated the effects of short exposure to the net on the blood feeding behavior of mosquitoes. The method for testing is shown in Figuer 1. A piece of Olyset® net affixed to a plywood panel was placed in a mosquito cage, and a plastic dish with a 1 cm diameter hole in it was placed upside down on the Olyset® net. Five adult female yellow fever mosquitoes (Aedes aegypti (L.)) were confined inside the dish for three minutes during which time they came in contact with the net. Afterwards, the dish was removed, and the mosquitoes were allowed to fly freely inside the cage. After one minute, a hand was inserted into the cage, and the number of mosquitoes landing on the hand to feed was counted for one minute (when mosquitoes landed on the hand, the hand was shaken to prevent actual biting).
Figure 1. Short exposure test method to determine the effect of Olyset® net on the biting behavior of female Aedes aegypti. The number of knocked down mosquitoes in the cage was also observed for 60 minutes. The number of landings on the hand and the knockdown results are shown in Figures 2 and 3 respectively. When the net was untreated, 40 insect landings per minute were observed, but with the Olyset® net, this fell to only five landings per minute. Knockdown results are recorded in Figure 2, which show significant levels of knockdown 10 minutes after contact, with some insects affected after 1 – 2 minutes. Observations indicated that mosquitoes that were in contact with Olyset® net for a short period of time were not able to recognize or respond to the host and did not show the probing activity normally associated with blood feeding insects .
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
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Figure 2. Knock down rate of Ae. aegypti after 3 minutes exposure to Olyset® net.
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Figure 3. Landing frequency of Ae. aegypti after 3 minutes exposure to Olyset® net.
A Field Trial to Control Malaria in Cambodia A field trial to control malaria was carried out by the National Malaria Center in a forested area 650 km northwest from Phnom Penh from June through December 1994 (4). The malaria vectors in this area are Anopheles dirus (Peyton and Harrison) and Anopheles minimus (Theobald). Malaria infections are approximately 60% falciparum malaria, 30% vivax malaria with about 10% mixed infections . There were 860 residents of the village where the Olyset® net was distributed and there were 1,000 residents in the village where untreated conventional mosquito nets were distributed. In an entomological survey conducted for two consecutive nights each month, mosquitoes were collected and their parous rate was determined. For an epidemiological survey,
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
the changes in the positive rate for malaria were examined by blood tests in 50 pre-selected children under 5 years old and 50 children 5 years old or older once per month. Out of the large amount of data, the transitions in the parous rate for Anopheles dirus are shown in Figure 4. The parous rate means the ratio of mosquitoes in the mosquito population that have experienced oviposition. In other words, a high parous rate means a high proportion of older mosquitoes in the population. After the malaria parasites have been taken into the body of the mosquito through feeding on an infected person, they develop to the sporozoite stage during two weeks inside the body of the mosquito and reach the salivary glands of the mosquito; then the parasite can be transmitted to a healthy person by injecting the sporozoites at the time of blood feeding. Therefore, having a large number of older mosquitoes means that the risk of a malarial infection is high. From Figure 4, it can be confirmed that the parous rate for the villages where Olyset® nets were distributed quickly dropped in comparison with the changes in the parous rate in the villages where untreated mosquito nets were distributed. It was suggested that mosquitoes were killed in contact with Olyset® nets, and an increase in the proportion of younger mosquitoes present was exhibited. Expanding on this further, it shows that as the number of mosquitoes that had reached the sporozoite stage became lower, and the risk of infection was decreased. Figure 5 shows the results of blood inspection in children. In the villages where Olyset® net was distributed, the positive rate for malaria became zero after three months. The positive rate for the villages where the untreated mosquito nets were distributed did not go to zero. From these field trials, it is clear that it is possible to effectively reduce or prevent malaria transmission through the use of Olyset® nets. O lyset net C onventional net
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Figure 4. Changes in parous rate of Anopheles dirus collcted inside house after Olyset® net treatment. (Drawn by the data from reference 4).
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
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Figure 5. Changes in malaria positive rate in children after Olyset® net treatment (Drawn by the data from reference 4). Several studies have been conducted to evaluate the longevity of Olyset® net in practical use conditions. Tami et al. collected 7 year old used Olyset® nets from two Tanzanian villages and examined insecticide dosage and biological efficacy. . The results show that permethrin content was 33-41% of the original content and these nets still exhibited a high knock down rate (5). Malima et al. examined insecticidal efficacy of seven-year old Olyset® nets in Tanzania and these used nets inhibited blood feeding by more than 95 % in tunnel tests (6). These results demonstrate that Olyset® nets still maintain insecticidal efficacy after 7 years under practical use conditions.
Olyset® Net for Dengue and Leishmaniasis Control The effects of Olyset net on dengue and leishmaniasis have also been reported. Nugyen et al. carried out a field experiment for dengue vector control using Olyset® net screens. The screens were set to windows, door entrance and ventilation openings near the ceiling. After installing Olyset® screens, the density index of Aedes aegypti was reduced from 0.23 to zero in contrast to the control area where the index increased (Figure 6). The larval Breteau Index and larval house index was also reduced to undetectable levels in the experimental area (7). Emani et al. used Olyset® net for leishmaniasis control in Iran. The results showed lower indoor density of P. papatasi Scopoli in the intervention area compared to the control area. From an epidemiological standpoint, there was a 97% reduction in anthroponotic cutaneous leishmaniasis (ACL) incidence compared to the control area (Figure 7) (8). These results strongly indicate that Olyset® net would be an important tool for dengue and leishmaniasis control.
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
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Fig. 6 Change in landing rate of Aedes aegypti in Olyset® net screen treated and untreated areas in Vietnam . (Drawn by the data from reference 7)
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Figure 7. Epidemiological survey for field trial of Olyset® net to control leishmaniasis in Iran. (Drawn by the data from reference 8)
Conclusiton Short exposure to Olyset® net results in significant bite inhibition activity and rapid knock down of mosquitoes. Field evaluations have shown that Olyset® net is an effective tool for controlling not only malaria but also dengue fever and leishmaniasis. As may be anticipated from these favorable results, Olyset® net is already being used in various situations for controlling vector borne diseases.
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
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References 1. 2. 3. 4. 5.
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WHO. Global Malaria Program, WHO Position Statement 2007. Geneva, WHO. http://www.who.int/malaria/docs/itn/ITNspospaperfinal.pdf Taklehaimanot A. ; Sachs J.D. ; Curtis C. ; Lancet, 2007, 369: 884 WHO/CDS/WHOPES/2001.4 16pp L Cheang, Y. ; Sandy L. ; National Malaria Center, Phnom Penh, Cambodia, 1994 Tami A. ; Mubyazi G. ; Talbert A. ; Mshinda H. ; Duchon S. ; Lengeler C. ; Malararia Journal 2004, 3, 19 Malima R.; Magesa S. ; Tunga P. ; Mwingira V. ; Magogo F. ; Sudi W. ; Mosha F. ; Curtis C. ; Maxwell C. ; Rowland M. ; Malaria Journal 2008, 7, 38 Nguyen H. T.; Tien T. V. ; Tien N. C. ; Ninh T. U. ; Hoa N. T.; Dengue Bulletin 1998 20, 87 Emami M. M. ; Yazdi M. ; Bashardoust N.; WHO Eestern Mediterrnean Region, Project No: SGS04-76, 2006
Clark et al.; Advances in Human Vector Control ACS Symposium Series; American Chemical Society: Washington, DC, 2009.
