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Interrupting the transmission of Chagas’ disease using insecticide-treated materials could be a cost-effective option, particularly for sylvatic vectors, which enter houses at night. A randomized trial was undertaken that included all houses in two communities in regions endemic for this disease, one in Venezuela (50 houses) and one in Colombia (47 houses). After a baseline study (including a short questionnaire survey, entomologic assessment, and Chagas’ disease serology), each household was randomly allocated to either the intervention group, which used pyre-throid-impregnated bed nets, or the control group, which used unimpregnated bed nets. Serologic analysis of children in the baseline study showed active transmission of Chagas’ disease in the Venezuelan community (10.7% of 103 children were positive), but none in the Colombian community (0% of 100 children were positive). Vectors were sylvatic and bugs entered the houses at night in both communities. The efficacy of pyrethroids against triatomine vectors was tested in Venezuela by exposing Rhodnius prolixus to lambdacyhalothrin-impregnated fabrics and in Colombia by residual house spraying with deltamethrin. This randomized trial showed that in both countries users of impregnated bed nets were well protected from vector bites (immediate benefit). The long-term effect on the community was high vector mortality. In Venezuela, all 62 vectors detected (mainly R. robustus) died within 72 hours of contact with impregnated bed nets. In houses that used unimpregnated nets, only 24.5% (13 of 53) of the vectors died (P < 0.001). The vectors most likely came from infested palm trees and they maintained transmission of the disease in this community (28.1% of 629 R. robustus were positive for Trypanosoma cruzi). Bioassays showed that the mortality rate of R. prolixus was 100% on lambdacyhalothrin-impregnated materials. In addition, in Colombia (the main vector was R. prolixus), the effect of repellent on vectors (driving them away from impregnated nets) was significant. Thus, users of impregnated bed nets are well protected from transmission of Chagas’ disease, and vector reduction or elimination can potentially be achieved in areas infested with R. prolixus and R. robustus.
Received August 29, 2002. Accepted for publication December 5, 2002.
Acknowledgments: We are indebted to the field staff in Venezuela (Ana Longa, Julio Mogollon, and Rafael Barazarte) and other members of the Centro de Investigación en Trujillo, particularly I. Galindez, for identifying the vectors, and the field staff in Colombia (Edison Devia Rojas, Jesús D Sarmiento, Isabel Machuca, and Panfilo Lobo) for their hard work during this study. We thank Elina Rojas in Venezuela and Marcos Restrepo (Medellin), and Florentino Celis (Cúcuta) in Colombia for exceptional support, and Syngenta and Agrego for donating the ICON® and K-Othrine, respectively. We also thank David Molyneux and Philip McCall (Liverpool), as well as Pierre Guillet (World Health Organization) for providing useful comments on drafts of the paper. Finally, we thank inhabitants of our study communities for bearing the inconveniences caused by our research; without their support, this study would not have been possible.
Financial support: This study was supported by the European Commission (contract ERBIC 18-CT98-0339) and the Alfa Program of the European Union (contract 94.04-6.0011.9).
Authors’ addresses: Axel Kroeger, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, United Kingdom, Telephone: 44-151-708-9393, Fax: 44-151-705-3364, E-mail: A.Kroeger{at}liverpool.ac.uk. Elci Villegas and José Vicente Scorza, Universidad de los Andes, Nucleo Trujillo, Venezuela, E-mail: elirojas{at}telcet.net.ve. José Ordoñez-Gonzalez, Colombian Institute of Tropical Medicine, Cra 43a, No. 52, Sur 99, Sabaneta, Antioquia, Colombia, E-mail: Jgog55{at}yahoo.com.mx. Eulides Pabon, Unidad de Control de Vectores, Cúcuta, Norte de Santander, Colombia, Telephone/Fax: 57-7-574-1753.
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