[Methodologic suggestion for the control of malaria and selection of measures applicable to different epidemiologic situations].
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The tank bromeliad Billbergia pyramidalis was treated with 2 doses (0.5 and 2 g) of ALTOSID Granules or Pellets for the control of Aedes aegypti L. Emergence inhibition (EI) for all mosquito pupae (including natural populations) in the center wells and leaf axils was > 90% for at least 6 and 12 months for both doses of granules and pellets, respectively. No significant difference in %EI was found between center wells and leaf axils.
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Since the Ministerial Conference on Malaria in 1992, which acknowledged the urgent need for worldwide commitment to malaria control, efforts have been directed to implementation of a Global Malaria Control Strategy. Vector control, an essential component of malaria control, has become less effective in recent years, partly as a result of poor use of alternative control tools, inappropriate use of insecticides, lack of an epidemiological basis for interventions, inadequate resources and infrastructure, and weak management. Changing environmental conditions, the behavioural characteristics of certain vectors, and resistance to insecticides have added to the difficulties. This report of a WHO Study Group provides guidelines for the planning, implementation and evaluation of cost-effective and sustainable vector control in the context of the Global Malaria Control Strategy. It reviews the available methods - indoor residual spraying, personal protection, larval control and environmental management - stressing the need for selective and flexible use of interventions according to local conditions. Requirements for data collection and the appropriate use of entomological parameters and techniques are discussed and priorities identified for the development of local capacity for vector control and for operational research. Emphasis is placed both on the monitoring and evaluation of vector control to ensure cost-effectiveness and on the development of strong managerial structures, which can support community participation and intersectoral collaboration and accommodate the control of other vector-borne diseases. The report concludes with recommendations aimed at promoting the targeted and efficient use of vector control in preventing and controlling malaria, thereby reducing the threat to health and socioeconomic development in many tropical countries.
Mosquito-borne diseases are responsible for significant human morbidity and mortality throughout the world. Efforts to control mosquito-borne diseases have been impeded, in part, by the development of drug-resistant parasites, insecticide-resistant mosquitoes, and environmental concerns over the application of insecticides. Therefore, there is a need to develop novel disease control strategies that can complement or replace existing control methods. One such strategy is to generate pathogen-resistant mosquitoes from those that are susceptible. To this end, efforts have focused on isolating and characterizing genes that influence mosquito vector competence. It has been known for over 70 years that there is a genetic basis for the susceptibility of mosquitoes to parasites, but until the advent of powerful molecular biological tools and protocols, it was difficult to assess the interactions of pathogens with their host tissues within the mosquito at a molecular level. Moreover, it has been only recently that the molecular mechanisms responsible for pathogen destruction, such as melanotic encapsulation and immune peptide production, have been investigated. The molecular characterization of genes that influence vector competence is becoming routine, and with the development of the Sindbis virus transducing system, potential antipathogen genes now can be introduced into the mosquito and their effect on parasite development can be assessed in vivo. With the recent successes in the field of mosquito germ line transformation, it seems likely that the generation of a pathogen-resistant mosquito population from a susceptible population soon will become a reality.
There has been a constant increase in the incidence of dengue in the Americas over the past 15 years. This has been caused by increased frequency of epidemic activity in most countries, as a result of increased numbers of virus serotypes circulating in the region. The change in disease ecology has resulted in the emergence of dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) in the region, first with a major epidemic in Cuba, followed by increased occurrence of sporadic cases of DHF/DSS in many countries. The sequence of events in the Americas in the 1980's has been nearly identical to the pattern observed in Southeast Asia in the 1950's. Prospects for prevention of epidemic DHF/DSS in the American region, therefore, are not good. In the absence of Aedes aegypti eradication, the only hope for effective prevention and control is to develop more effective active surveillance for DHF/DSS and combine that with both emergency and community-based vector control programs.
In the summer of 1998, failures of methoprene field applications to control the mosquito Ochlerotatus nigromaculis (Ludlow) were noticed in several pastures in the outskirts of Fresno, California, USA. Effective control with methoprene had been achieved for over 20 years prior to this discovery. Susceptibility tests indicated that the Fresno Oc nigromaculis populations had developed several thousand-fold higher LC50 and LC90 tolerance levels to methoprene compared with methoprene-naïve populations. The synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate and 3-octylthio-1,1,1-trifluoro-2-propanone had little synergistic effect, suggesting that the mechanism of methoprene tolerance was not mediated by P450 monooxygenase or carboxylesterase enzyme degradation. As part of initiating a resistance management strategy, partial reversion back to methoprene susceptibility was achieved in a resistant population after six consecutive applications of Bacillus thuringiensis israelensis Goldberg & Marga coupled with two oil and two pyrethrum + PBO applications.
Malaria transmission rates and risks can be greatly reduced by vector control, mitigating high malaria incidence and prevalence rates. Methods and strategies for malaria vector control (MVC) have been well documented by WHO, although its implementation varies widely. Technical guidelines for MVC strategies and materials are readily available, but the status and role of MVC have not been reviewed and redefined in terms of programme management and resource allocation. There are huge changes since November 1993 when the last WHO Study Group reviewed vector control for malaria and other mosquito-borne diseases, following the 1992 adoption of the Global Malaria Control Strategy. Operationally, with reform of the health sector in many countries, the centrally managed and vertically structured malaria control programme (MCP) has been superseded by a community-based and decentralized one. This poses challenges for effective implementation of MVC strategies. Therefore it became evident that the role of vector control in malaria control needs to be reconsidered to develop a strategic framework for MVC implementation by national malaria control programmes and other partners. This report of a WHO Study Group on Malaria Vector Control and Personal Protection reviewed the current vector control strategies and their effectiveness in various operational and eco-epidemiological settings, and identified challenges for implementation in different health systems. An outline strategic framework for strengthening malaria vector control implementation was developed. The process of deciding about which mosquito control method is appropriate in a given situation should be guided by an analysis of the level of malaria endemicity and vector bionomics, the eco-epidemiological setting, the health management system and an estimate of the programme sustainability. This report also provides a basis for the development of a strategic framework for strengthening malaria vector control implementation.
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The influence of WR-238605 (8-[(4-amino-1-methyl-butyl) amino]-2,6-dimethoxy-4-methyl-5-[3-tri-fluoromethylphenoxyl] quinoline succinate) on the sporogonic development of a Plasmodium berghei ANKA clone was determined. Anopheles stephensi were fed on P. berghei infected mice treated 90 min earlier with 25 or 50 mg WR-238605/kg body weight. Mosquitoes engorging on drug-treated mice produced the same number of ookinetes as did those fed on controls; drug-fed mosquitoes produced fewer oocysts/mosquito than did controls. These oocytes developed more slowly than did those in control-fed mosquitoes. Sporozoites did not invade the salivary glands of drug-fed mosquitoes, nor did these mosquitoes transmit P. berghei to mice. Uptake of WR-238605 6 or 12 days after mosquitoes were infected with P. berghei had no effect on the percentage of mosquitoes with oocysts or the mean number of oocysts produced per mosquito. Oocyst development was significantly retarded in mosquitoes ingesting drug on day 6 postinfection. Subsequent salivary gland sporozoite infections were lighter in mosquitoes drug-fed on day 6 or day 12 than in control mosquitoes or mosquitoes drug-fed on day 18. These data indicate that WR-238605 has significant sporontocidal activity.
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