Effectiveness and acceptance of total release insecticidal aerosol cans as a control measure in reducing dengue vectors.

Author:Pai, Hsiu-Hua
Position:INTERNATIONAL PERSPECTIVES - Report
 
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Introduction

Dengue has emerged as an international public health problem (Jacobs, 2000). This mosquito-borne viral infection is endemic in more than 100 countries of Africa, Central and South America, Asia, and the Western Pacific (Castleberry & Mahon, 2003). Although the etiologic agents (DEN-1, DEN2, DEN-3, and DEN-4) and principal vectors (Aedes aegypti and Ae. albopictus) are well studied, no specific management of the clinical cases exists. In addition, vaccines against dengue remain commercially unavailable. Vector control is considered the only strategy to control the transmission of the disease (Guzman & Kouri, 2002). Elimination of adult mosquitoes in the endemic area is one of the general approaches to dengue control. The World Health Organization (WHO) has documented that space-spray is effective against adult mosquitoes in dengue control activities (WHO, 1996).

As a principal vector, Ae. aegypti is able to transmit dengue at temperatures over 20[degrees]C. It loses this capability, however, below 16[degrees]C (Blanc & Caminopetros, 1930). This species has a flight range of 25 m to over 100 km in open areas and may fly 2.5 km/day (Wolfinsohn & Galun, 1953). Ae. albopictus may also transmit dengue (Sabin, 1952). In Taiwan, Ae. albopictus distributes throughout the island whereas Ae. aegypti is commonly found in the regions south of the Tropic of Cancer. Ae. aegypti breeds in artificial water containers such as vessels and discarded tires whereas Ae. albopictus breeds in natural ones such as tree holes (Teng, 1996). The abundance of these two species has seasonal variations. Ae. albopictus was found to have a significantly higher proportion than Ae. aegypti throughout the year (Pai & Lu, 2009).

The first records of dengue in Taiwan can be traced back to 1870. Since then, a number of epidemics have occurred (Ko, 1989). In 1981, an outbreak occurred on Liouchyou district, an offshore island in southwest Taiwan. The causative agent was identified to be DEN-2 and it was probably imported from the Philippines (Hsieh et al., 1982; Wu, 1986). Between 1987 and 1988, another outbreak due to DEN-1 appeared in South Taiwan and more than 10,000 cases were reported (Ko, 1989). After subsiding for two years, dengue reemerged in 1991, although the severity was milder (Harn, Chiang, Tian, Chang, & Ko, 1993). In addition to the southern part of the island, an outbreak also affected Taipei County of North Taiwan in 1995 (Teng et al., 1998). In June 2002, more than 5,000 cases of dengue fever and 241 cases of dengue hemorrhagic fever were reported in South Taiwan. Due to an extensive history of dengue burden, control measures such as early case detection in sentinel health facilities, early warning systems, and prompt extensive vector control have been applied in this region.

As a general control measure, insecticidal fogging is regularly administered to endemic and/or nonendemic areas in South Taiwan. The effectiveness of this control strategy is questionable, however, since delays occur between peak time of outbreak and insecticide administrations. Many residents refuse to allow government workers to conduct indoor insecticidal fogging because of concern over insecticide contamination of household items. WHO has recommended the use of personal protective measures such as aerosol insecticide spraying at home and in the peridomestic environment (WHO, 1997). In order to evaluate the effectiveness and acceptance of the personal use of insecticidal aerosols as a measure to reduce dengue fever vectors, we provided residents in experimental household groups with different formulations of total release insecticidal aerosol cans. The effectiveness of these formulations and insecticidal fogging in reducing dengue vector populations were compared by ovitrap index. The acceptance of these measures was also evaluated by a questionnaire.

Methods

Study Areas and Insecticidal Aerosol Can Formulations

Our study, conducted in May 2006, was approved by the Department of Environmental Sanitation and Toxic Substance Management, Environmental Protection Administration, Executive Yuan, Republic of China. Three boroughs were selected randomly from each of two randomly selected districts of Kaohsiung City in South Taiwan and divided into three experimental groups. In the first treatment group, insecticidal fogging was administered indoor and outdoor by the government.

In addition to the dengue surveillance measures (Center for Disease Control, Republic of China, 2003) and insecticidal fogging administered outdoor by the government, households in the other two experimental groups were provided with one of two formulations of total release insecticidal aerosol cans (permethrin 3.75% weight/weight [w/w] and cypermethrin 1.716% w/w) for indoor personal administration. The aims, application procedures, and cautions of our study were clearly explained to the participants by well-trained inspectors. These cans were then returned to our laboratory to determine the status of usage.

Application of Insecticidal Aerosol Cans

Before release of the insecticidal aerosol, the residents were requested to keep their windows and doors closed and to cover all food materials and drinking water. The content of each aerosol can was applied to an area of 11 [m.sup.2]. Each can was placed in the center of the room before pressing the button on the can to release the insecticidal aerosol in about 60 seconds. The windows and doors were then opened 30 minutes later. These cans were then returned to our laboratory to determine the status of usage.

Evaluation...

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