Dengue prevention at the household level: preliminary evaluation of a mesh cover for flowerpot saucers
Prevención domiciliar de la dengue: evaluación preliminar de tela protectora para platos de macetas de planta
Virgínia Torres Schall; Héliton da Silva Barros; João Bosco Jardim; Nágila Francinete Costa Secundino; Paulo Filemon Paolucci Pimenta
Centro de Pesquisas René Rachou. Fundação Oswaldo Cruz. Belo Horizonte, MG, Brasil
The effectiveness of a polyester mesh cover (evidengue®), aimed at preventing the access of female Aedes aegypti mosquitoes to flowerpot saucers, was evaluated in laboratory. Two saucers of flowerpot with water were individually wrapped with the cover was placed with their respective pots in two entomological cages. One identical set of flowerpot and saucer was placed in a third cage. In each cage, 20 gravid females, fed on mouse blood, were released. Results show that the cover was effective to prevent access of females. Further tests are necessary to assess cover effectiveness as a device to prevent saucer oviposition.
Descriptors: Aedes aegypti. Oviposition. Mesh covers. Flowerpot saucers. Evidengue®.
Se evaluó en laboratorio la eficiencia de una cubierta de tela de polyester (evidengue®) con el objetivo de vedar el acceso de hembras del mosquito Aedes aegypti a platos de macetas de planta. Fueron utilizadas tres jaulas entomológicas, dos de ellas con evidengue® y una para control. En cada jaula fueron colocados dos conjuntos de macetas de planta y platos y 20 hembras copuladas, alimentadas con sangre de ratón. Los resultados muestran que la cubierta fue eficaz como barrera al acceso de hembras. Nuevas pruebas son necesarias para evaluar la eficiencia de la cubierta como dispositivo de prevención de la oviposición en los platos.
Descriptores: Dengue, epidemiología. Factores de Riesgo. Factores Socioeconómicos. Vigilancia Epidemiológica. Estudios Ecológicos.
Studies performed in dengue-endemic countries show that mosquito-proof mesh covers can block the access of female Aedes aegypti, the main dengue vector, to the interior of household water containers and, in this way, prevent oviposition and larval development in them.3,4,6,7 The use of unsealed flowerpot saucers makes these containers potential breeding sites for Ae. aegypti. However, no studies have been performed to evaluate the effectiveness of mesh covers in these containers.1,2,5
The present communication describes a preliminary laboratory evaluation of a prototype polyester mesh cover for flowerpot saucers (evidengue®), now being developed at the Laboratório de Educação em Saúde, Centro de Pesquisa René Rachou, Fundação Oswaldo, Fiocruz Minas (Laboratory of Health Education, René Rachou Research Center, Oswaldo Cruz Foundation, Fiocruz Minas).
Evidengue®a is a round mosquito mesh cover, manufactured with a polyester synthetic resin mesh equal to or smaller than 2 mm x 1 mm. The prototype evaluated (Figure) has a frill along its opening rim, where a strap of the same material and a rubber band are embedded. The strap and the band allow the fitting of evidengue® to the flowerpot. When properly adjusted, evidengue® prevents female Ae. aegypti access to the saucer completely.
Two black plastic flowerpot saucers with 11 cm in diameter, each containing 220 ml of unchlorinated water, were individually wrapped with evidengue® (maximum opening of 18 cm in diameter) and placed with their respective flowerpots in two entomological cages (A and B) of 40 cm x 40 cm x 40 cm in size, one in each cage. One identical flowerpot and saucer set, with the same amount of unchlorinated water, was placed without evidengue® in a third cage (C) of the same dimensions. A total of 20 gravid female Ae. aegypti, bred in laboratory, were placed into each cage to evaluate the mesh cover effectiveness as an access blocking and, consequently, saucer oviposition prevention device. Females were put into the cages, four days after receiving a blood meal from an anesthetized mouse. The procedure was initially performed only in cage A and, ten days after data collection, simultaneously in cages B and C. This interval between procedures was adopted due to female feeding to perform the replica. Cage A was opened on the fifth day, following placement of females; cages B and C, on the eighth day. After cages were opened, it was observed whether there were females inside the evidengue®, as well as larvae in the water and eggs on the flowerpot and saucer surfaces adjacent to the water. Eggs were not counted.
Females, eggs or larvae were not found inside the evidengue®. Persistent movements towards the evidengue® were observed during mosquito flight. In cages A and B, females were seen on the lateral surfaces and on the bottom more frequently. No eggs were found on the surfaces of evidengue®. In cage C, there were eggs on the part of the flowerpot surface adjacent to the water line and four first-stage larvae actively swimming in the saucer.
Evidengue® was found to be 100% effective to block access of female Ae. aegypti to the flowerpot saucers. This result, however, is limited to a replica of cage A and one control cage only. Further laboratory evaluations are necessary, with a greater number of saucers in both conditions and egg count in each replica. Nevertheless, the mere test of evidengue® in laboratory is insufficient to assess the cover effectiveness as an oviposition prevention device for flowerpot saucers. Evaluations in open air and inside homes are also necessary to verify how proficiently the user blocks mosquito access to standing water in the saucer. In addition, a durability assessment of evidengue® under different conditions of use is necessary.
One critical aspect to be assessed is the maintenance of the evidengue® adjustable ribbon and rubber band to a height of the flowerpot which is far enough from the saucer to prevent that possible mesh lowering (resulting from manual pressure or rain, for example) enables mosquito oviposition in puddles formed by water coming out through the mesh. The Ministério da Saúde (Brazilian Ministry of Health) recommends the addition of sand to avoid oviposition inside the saucer. However, unless there is frequent renewal, such measure does not prevent water to gather above the sand level. Only by completely blocking mosquito access to the water will oviposition and larval development in containers be prevented.
Results from a nationwide Aedes aegypti infestation index rapid surveyb show that flowerpot saucers have become one of the most frequent Ae. aegypti breeding sites of homes in the Center-West and Southeastern regions of Brazil. Apparently, indoor plant gardening in pots has become a habit resistant to change in many cities of the country. Considering the insufficient chemical vector control inside homes and the low population adherence to official recommendations to control domestic water container use, it is reasonable to assume that evidengue® effectiveness as an Ae. aegypti oviposition prevention device in flowerpot saucers can be an alternative that, rather than changing this habit, will contribute to maintain it safely.
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Virgínia Torres Schall
Centro de Pesquisas René Rachou
Fundação Oswaldo Cruz
Av. Augusto de Lima, 1715 - Barro Preto
30190-002 Belo Horizonte, MG, Brasil
Research funded by the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (Fapemig - State of Minas Gerais Research Support Foundation; Process n.: CBB-568-04).
Schall VT was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - National Council for Scientific and Technological Development - Proc. n.: 302231/2008-0; Research Productivity Scholarship).
b Ministério da Saúde. Portal SUS. Saúde divulga novo mapa da dengue no Brasil. [cited 2009 Aug 19] Available from: http://www.sus20anos.saude.gov.br/sus20anos/portal/index.php?option=com_content&view=article&catid=1%3Anacionais&id=625%3Asaude-divulga-novo-mapa-da-dengue-no-brasil-&Itemid=34
a Schall VT, inventor: Fapemig/Fiocruz/MG Patente MU8303239-8. 28/11/2003.