What role for insecticides in vector control programs?
ABSTRACT Vector-borne diseases including dengue, yellow fever, Japanese encephalitis, malaria, leishmaniasis, and filariasis remain severe public health problems in most of the countries in which they are endemic. In some cases, their incidence is increasing and they are spreading to new geographic areas. For a number of the infections, the most effective manner of controlling their transmission is through control of their vectors. However, in some instances, such as dengue and Chagas' disease, there is no alternative. Most countries that are endemic for vector-borne diseases maintain vector control services, and most large tropical and semitropical cities also have pest control programs, mainly against pest mosquitoes. Virtually all of the vector and pest control programs depend on the use of insecticides formulated as larvicides, adulticides, baits, or insecticide impregnated bed nets. For many years, the development of new insecticides for use in public health programs was encouraged and supported by multilateral and bilateral health agencies, including the implementation of field trials in endemic areas. Due to the development of insecticide resistance, toxicologic and environmental considerations, and the cost of development and of registration, the number of compounds available for use has declined while the number of new insecticides submitted for laboratory and field trials to the World Health Organization has dwindled even more. The recrudescence of vector-borne diseases, the rapid pace of urbanization, lagging development of environmental services in many tropical cities, and difficulties encountered in ensuring the community's cooperation in its own protection through environmental measures make imperative the continued availability of pesticides for public health use. Since only the pesticide manufacturing industry has the combination of technical and financial resources to promulgate the research and development of new pesticides and pesticide groups, it is suggested that governments, bilateral, and multilateral organizations explore the manner in which they can assist industry in the development of new compounds and guarantee the continued availability of effective and safe pesticides for vector-control programs.
- SourceAvailable from: Hamadttu Elshafie[Show abstract] [Hide abstract]
ABSTRACT: Mosquitoes, as blood sucking insects and vectors for several serious human diseases, continue to be one of the major threats to public health, comfort and economic growth in the Sudan and many other countries. Dengue, yellow fever, and filariasis in addition to malaria are all transmitted by mosquitoes; this pest is controlled using chemical pesticides. The increasing concern about the environment and the hazards resulting from the sole reliance on pesticides and the acquired resistance to one or multiple insecticides forced scientist to seek for safer efficient alternatives or supplements for the chemical pesticides. Bacillus thuringiensis is considered to be one of the important microbial control agents capable of producing insecticidal proteins with specific pathogenicity. In this study, different samples were obtained from soils collected from different locations in Sudan and from stored products dust and dead insects, in addition to mosquito rearing bonds, with the objective of isolating entomopathogenic Bacillus thuringiensis strains. Thirty nine strains were isolated and identified morphologically and biochemically and their toxicity to the house mosquito Culex quinquefasciatus second and third instar larvae was evaluated. The larvae of the house mosquito were introduced to sterile distilled water treated with 500 ppm concentration from each isolate. Significant differences existed between the isolates in their toxicity 42 hours post treatment, where mortality percentages ranged from 25% to 95% compared to 12.5% in the untreated control larvae. About 69% of the 39 Bt isolates were found pathogenic (mortality ≥50%) to the house mosquito larvae. Regression analysis revealed differences in the lethal times between the different isolates. The LT 50 values varied from 29.38 hours for isolate Om-5 to 131.9956 hours for isolate GF-18. The practical significance of these findings for management of mosquitoes is discussed. It is therefore concluded that Sudan environment is rich in Bacillus thuringiensis pathogenic to the house mosquito and 5 isolates resulted in cumulative mortality percentages above 80%.
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ABSTRACT: To study the microbial communities in three sites contaminated with chlorinated pesticides and evaluation of dehydrodechlorinase (linA) gene variants involved in gamma-hexachlorocyclohexane (γ-HCH, lindane) degradation. Using a culture-independent method, 16S rRNA genes were amplified from microbial communities occurring in contaminated soils. From 375 clone libraries analysed, 55 different restriction fragment length polymorphism phylotypes were obtained. Dehydrodechlorinase (linA) gene, which initiates the γ-HCH degradation, was directly amplified by PCR from the DNA extracted from soils. Deduced amino acid sequences of eight variant genotypes of linA showed few amino acid changes. All the variants of linA had mutations of F151L and S154T, and one of the genotype carried 12 amino acid changes when compared to a linA of Sphingomonas sp. reported from the same soil. The microbial communities displayed complex and diverse groups similar to bacteria involved in biodegradation. The presence of biodegradative genes like linA indicates the presence of communities with capacity to biodegrade the persistent pesticide HCH. This study provides insights to evaluate the presence of catabolic genes and assessing the bioremediation potential of the industrial soils contaminated by chlorinated pesticides.Journal of Applied Microbiology 10/2010; 109(4):1458-68. DOI:10.1111/j.1365-2672.2010.04781.x · 2.39 Impact Factor
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ABSTRACT: Screening of natural products for mosquito larvicidal activity against three major mosquito vectors Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi resulted in the identification of three potential plant extracts viz., Saraca indica/asoca, Nyctanthes arbor-tristis, and Clitoria ternatea for mosquito larval control. In the case of S. indica/asoca, the petroleum ether extract of the leaves and the chloroform extract of the bark were effective against the larvae of C. quinquefasciatus with respective LC(50) values 228.9 and 291.5 ppm. The LC(50) values of chloroform extract of N. arbor-tristis leaves were 303.2, 518.2, and 420.2 ppm against A. aegypti, A. stephensi, and C. quinquefasciatus, respectively. The methanol and chloroform extracts of flowers of N. arbor-tristis showed larvicidal activity against larvae of A. stephensi with the respective LC(50) values of 244.4 and 747.7 ppm. Among the methanol extracts of C. ternatea leaves, roots, flowers, and seeds, the seed extract was effective against the larvae of all the three species with LC(50) values 65.2, 154.5, and 54.4 ppm, respectively, for A. stephensi, A. aegypti, and C. quinquefasciatus. Among the three plant species studied for mosquito larvicidal activity, C. ternatea was showing the most promising mosquito larvicidal activity. The phytochemical analysis of the promising methanolic extract of the seed extract was positive for carbohydrates, saponins, terpenoids, tannins, and proteins. In conclusion, bioassay-guided fractionation of effective extracts may result in identification of a useful molecule for the control of mosquito vectors.Parasitology Research 12/2008; 104(5):1017-25. DOI:10.1007/s00436-008-1284-x · 2.33 Impact Factor