Optimizing insecticide allocation strategies based on houses and livestock shelters for visceral leishmaniasis control in Bihar, India.

Visceral leishmaniasis (VL) is the most deadly form of the leishmaniasis family of diseases, which affects numerous developing countries. The Indian state of Bihar has the highest prevalence and mortality rate of VL in the world. Insecticide spraying is believed to be an effective vector control program for controlling the spread of VL in Bihar; however, it is expensive and less effective if not implemented systematically. This study develops and analyzes a novel optimization model for VL control in Bihar that identifies an optimal (best possible) allocation of chosen insecticide (dichlorodiphenyltrichloroethane [DDT] or deltamethrin) based on the sizes of human and cattle populations in the region. The model maximizes the insecticide-induced sandfly death rate in human and cattle dwellings while staying within the current state budget for VL vector control efforts. The model results suggest that deltamethrin might not be a good replacement for DDT because the insecticide-induced sandfly deaths are 3.72 times more in case of DDT even after 90 days post spray. Different insecticide allocation strategies between the two types of sites (houses and cattle sheds) are suggested based on the state VL-control budget and have a direct implication on VL elimination efforts in a resource-limited region.

Application of the malaria management model to the analysis of costs and benefits of DDT versus non-DDT malaria control.

INTRODUCTION: DDT is considered to be the most cost-effective insecticide for combating malaria. However, it is also the most environmentally persistent and can pose risks to human health when sprayed indoors. Therefore, the use of DDT for vector control remains controversial. METHODS: In this paper we develop a computer-based simulation model to assess some of the costs and benefits of the continued use of DDT for Indoor Residual Spraying (IRS) versus its rapid phase out. We apply the prototype model to the aggregated sub Saharan African region. For putting the question about the continued use of DDT for IRS versus its rapid phase out into perspective we calculate the same costs and benefits for alternative combinations of integrated vector management interventions. RESULTS: Our simulation results confirm that the current mix of integrated vector management interventions with DDT as the main insecticide is cheaper than the same mix with alternative insecticides when only direct costs are considered. However, combinations with a stronger focus on insecticide-treated bed nets and environmental management show higher levels of cost-effectiveness than interventions with a focus on IRS. Thus, this focus would also allow phasing out DDT in a cost-effective manner. Although a rapid phase out of DDT for IRS is the most expensive of the tested intervention combinations it can have important economic benefits in addition to health and environmental impacts that are difficult to assess in monetary terms. Those economic benefits captured by the model include the avoided risk of losses in agricultural exports. CONCLUSIONS: The prototype simulation model illustrates how a computer-based scenario analysis tool can inform debates on malaria control policies in general and on the continued use of DDT for IRS versus its rapid phase out in specific. Simulation models create systematic mechanisms for analyzing alternative interventions and making informed trade offs.

Global status of DDT and its alternatives for use in vector control to prevent disease.

OBJECTIVE: I review the status of dichlorodiphenyltrichloroethane (DDT), used for disease vector control, along with current evidence on its benefits and risks in relation to the available alternatives. DATA SOURCES AND EXTRACTION: Contemporary data on DDT use were largely obtained from questionnaires and reports. I also conducted a Scopus search to retrieve published articles. DATA SYNTHESIS: DDT has been recommended as part of the arsenal of insecticides available for indoor residual spraying until suitable alternatives are available. Approximately 14 countries use DDT for disease control, and several countries are preparing to reintroduce DDT. The effectiveness of DDT depends on local settings and merits close consideration in relation to the alternatives. Concerns about the continued use of DDT are fueled by recent reports of high levels of human exposure associated with indoor spraying amid accumulating evidence on chronic health effects. There are signs that more malaria vectors are becoming resistant to the toxic action of DDT, and that resistance is spreading to new countries. A comprehensive cost assessment of DDT versus its alternatives that takes side effects into account is missing. Effective chemical methods are available as immediate alternatives to DDT, but the choice of insecticide class is limited, and in certain areas the development of resistance is undermining the efficacy of insecticidal tools. New insecticides are not expected in the short term. Nonchemical methods are potentially important, but their effectiveness at program level needs urgent study. CONCLUSIONS: To reduce reliance on DDT, support is needed for integrated and multipartner strategies of vector control and for the continued development of new technologies. Integrated vector management provides a framework for developing and implementing effective technologies and strategies as sustainable alternatives to reliance on DDT.

"The horizon opened up very greatly": Leland O. Howard and the transition to chemical insecticides in the United States, 1894-1927.

The transition to synthetic chemicals as a popular method of insect control in the United States was one of the most critical developments in the history of American agriculture. Historians of agriculture have effectively identified the rise and charted the dominance of early chemical insecticides as they came to define commercial agriculture between the emergence of Paris green in the 1870s and the popularity of DDT in the 1940s and beyond. Less understood, however, are the underlying mechanics of this transition. this article thus takes up the basic question of how farmers and entomologists who were once dedicated to an impressively wide range of insect control options ultimately settled on the promise of a chemically driven approach to managing destructive insects. Central to this investigation is an emphasis on the bureaucratic maneuverings of Leland O. Howard, who headed the Bureau of Entomology from 1894 to 1927. Like most entomologists of his era, Howard was theoretically interested in pursuing a wide variety of control methods--biological, chemical, and cultural included. In the end, however, he employed several tactics to streamline the government's efforts to almost exclusively support arsenic and lead-based chemical insecticides as the most commercially viable form of insect control. While Howard in no way "caused" the national turn to chemicals, this article charts the pivotal role he played in fostering that outcome.

DDT reintroduction for malaria control: the cost-benefit debate for public health.

DDT is a persistent insecticide that was widely used in the world from the 1940s until the 70s, when it was banned in the United States and other countries. Most of its toxic effects are not observed in the acute forms, but particularly after chronic exposure. These long-term issues include reproductive effects, varying according to the time of life in which the individuals were exposed. The aims of the current study were to review the principal toxicological effects of DDT on reproduction, stratifying by physiological periods of exposure, and based on the magnitude of these effects, to discuss the cost-benefit relationship of reintroducing DDT with the specifically defined vector control criteria.

Dichlorodiphenyltrichloroethane (DDT) for indoor residual spraying in Africa: how can it be used for malaria control?

In 2006, the World Health Organization issued a position statement promoting the use of indoor residual spraying (IRS) with dichlorodiphenyltrichloroethane (DDT) for malaria vector control in epidemic and endemic areas. Other international organizations concurred because of the great burden of malaria and the relative ineffectiveness of current treatment and control strategies. Although the Stockholm Convention of 2001 targeted DDT as 1 of 12 persistent organic pollutants for phase-out and eventual elimination, it allowed a provision for its continued indoor use for disease vector control. Although DDT is a low-cost antimalarial tool, the possible adverse human health and environmental effects of exposure through IRS must be carefully weighed against the benefits to malaria control. This article discusses the controversy surrounding the use of DDT for IRS; its effective implementation in Africa; recommendations for deployment today, and training, monitoring, and research needs for effective and sustainable implementation. We consider the costs and cost effectiveness of IRS with DDT, alternative insecticides to DDT, and the importance of integrated vector control if toxicity, resistance, and other issues restrict its use.

The cost and cost-effectiveness of malaria vector control by residual insecticide house-spraying in southern Mozambique: a rural and urban analysis.

OBJECTIVES: To compare two separately funded, but operationally similar, residual household-spraying (RHS) initiatives; one rural and one peri-urban in southern Mozambique. METHODS: The rural programme is a regional project involving the participation and co-ordination of organizations across three countries in southern Africa and is focussed on control in an area in Mozambique of 7552 km2. The second programme focuses on spraying a peri-urban community within a 10-km radius around MOZAL, an aluminium smelter plant of area 410 km2. An ingredients approach was used to derive unit costs for both the rural and peri-urban spraying programmes using detail retrospective cost data and effectiveness indicators. RESULTS: The economic cost per person covered per year using Carbamates for indoor residual spraying (IRS) in the rural area, excluding the costs of project management and monitoring and surveillance was $3.48 and in the peri-urban area, $2.16. The financial costs per person covered in the rural area and peri-urban area per year were $3.86 and $2.41, respectively. The economic costs per person covered were respectively increased by 39% and 31% when project management and monitoring and surveillance were included. The main driving forces behind the costs of delivering RHS are twofold: the population covered and insecticide used. Computed economic and financial costs are presented for all four insecticide families available for use in RHS. CONCLUSIONS: The results from both these initiatives, especially the rural area, should be interpreted as conservative cost estimates as they exclude the additional health gains that the newly introduced programmes have had on malaria rates in the neighbouring areas of South Africa and Swaziland. Both these initiatives show that introducing an IRS programme can deliver a reduction in malaria-related suffering providing financial support, political will, collaborative management and training and community involvement are in place.

Cost-effectiveness and sustainability of lambdacyhalothrin-treated mosquito nets in comparison to DDT spraying for malaria control in western Thailand.

The cost-effectiveness of lambdacyhalothrin-treated nets in comparison with conventional DDT spraying for malaria control among migrant populations was evaluated in a malaria hyperendemic area along the Thai-Myanmar border. Ten hamlets of 243 houses with 948 inhabitants were given only treated nets. Twelve hamlets of 294 houses and 1,315 population were in the DDT area, and another 6 hamlets with 171 houses and 695 inhabitants were in the non-DDT-treated area. The impregnated net program was most cost-effective (US$1.54 per 1 case of prevented malaria). Spraying with DDT was more cost-effective than malaria surveillance alone ($1.87 versus $2.50 per 1 case of prevented malaria). These data suggest that personal protection measures with insecticide-impregnated mosquito net are justified in their use to control malaria in highly malaria-endemic areas in western Thailand.

Cost-comparison of DDT and alternative insecticides for malaria control.

In anti-malaria operations the use of DDT for indoor residual spraying has declined substantially over the past 30years, but this insecticide is still considered valuable for malaria control, mainly because of its low cost relative to alternative insecticides. Despite the development of resistance to DDT in some populations of malaria vector Anopheles mosquitoes (Diptera: Culicidae), DDT remains generally effective when used for house-spraying against most species of Anopheles, due to excitorepellency as well as insecticidal effects. A 1990 cost comparison by the World Health Organization (WHO) found DDT to be considerably less expensive than other insecticides, which cost 2 to 23 times more on the basis of cost per house per 6 months of control. To determine whether such a cost advantage still prevails for DDT, this paper compares recent price quotes from manufacturers and WHO suppliers for DDT and appropriate formulations of nine other insecticides (two carbamates, two organophosphates and five pyrethroids) commonly used for residual house-spraying in malaria control programmes. Based on these 'global' price quotes, detailed calculations show that DDT is still the least expensive insecticide on a cost per house basis, although the price appears to be rising as DDT production declines. At the same time, the prices of pyrethroids are declining, making some only slightly more expensive than DDT at low application dosages. Other costs, including operations (labour), transportation and human safety may also increase the price advantages of DDT and some pyrethroids vs. organophosphates and carbamates, although possible environmental impacts from DDT remain a concern. However, a global cost comparison may not realistically reflect local costs or effective application dosages at the country level. Recent data on insecticide prices paid by the health ministries of individual countries showed that prices of particular insecticides can vary substantially in the open market. Therefore, the most cost-effective insecticide in any given country or region must be determined on a case-by-case basis. Regional coordination of procurement of public health insecticides could improve access to affordable products.

Cost-effectiveness analysis of lambdacyhalothrin-treated nets for malaria control: the patients' perspective.

The present study was undertaken to evaluate the cost-effectiveness of lambdacyhalothrin-treated nets in comparison with conventional DDT-spraying as a method of malaria control according to the patients' perspective among migrant populations in a high-risk area along the Thai-Myanmar border in Thailand. Ten hamlets comprising 243 houses with 948 inhabitants were given only treated nets. Twelve hamlets comprising 294 houses and 1,315 inhabitants represented the DDT-treated area and another six hamlets with 171 houses and 695 inhabitants served as controls. Information as to consumer costs was obtained by interviewing 3,214 patients seeking care at all levels of the health care system in the study area. Analysis showed that the impregnated-net program was more cost-effective than the DDT-spraying program or surveillance alone (US$ 0.59 vs US$ 0.74 vs US$ 0.79 per 1 case of prevented malaria). We conclude that in a high-risk area such as along the Thai-Myanmar border in western Thailand, integrating the use of impregnated nets with large-scale primary health care programs is likely to constitute the most cost-effective method for controlling malaria according to the patients' perspective.

'No other logical choice': global malaria eradication and the politics of international health in the post-war era.

In 1955 the Eighth World Health Assembly voted to initiate a program for the global eradication of malaria. The global eradication of malaria represented a remarkable leap of faith. Many health authorities, both within and outside the Assembly, viewed eradication as at best fool hardy, and at worst, potentially disastrous. To understand why the World Health Assembly went ahead with a Global Eradication strategy, despite these concerns, it is necessary to examine the politics of international health and development in the post-war era. This political context shaped decisions about the adoption of DDT as a primary tool in the fight against malaria, as well as the adoption of the Malaria Eradication Program. It is equally important to understand how the advocates of an eradication strategy shaped arguments and developed support for their cause in the years leading up to the Eighth World Health Assembly meeting.

DDT, global strategies, and a malaria control crisis in South America.

Malaria is reemerging in endemic-disease countries of South America. We examined the rate of real growth in annual parasite indexes (API) by adjusting APIs for all years to the annual blood examination rate of 1965 for each country. The standardized APIs calculated for Brazil, Peru, Guyana, and for 18 other malaria-endemic countries of the Americas presented a consistent pattern of low rates up through the late 1970s, followed by geometric growth in malaria incidence in subsequent years. True growth in malaria incidence corresponds temporally with changes in global strategies for malaria control. Underlying the concordance of these events is a causal link between decreased spraying of homes with DDT and increased malaria; two regression models defining this link showed statistically significant negative relationships between APIs and house-spray rates. Separate analyses of data from 1993 to 1995 showed that countries that have recently discontinued their spray programs are reporting large increases in malaria incidence. Ecuador, which has increased use of DDT since 1993, is the only country reporting a large reduction (61%) in malaria rates since 1993. DDT use for malaria control and application of the Global Malaria Control Strategy to the Americas should be subjects of urgent national and international debate. We discuss the recent actions to ban DDT, the health costs of such a ban, perspectives on DDT use in agriculture versus malaria control, and costs versus benefits of DDT and alternative insecticides.

Is DDT use a public health problem in Mexico?

We review the potential impact of DDT on public health in Mexico. DDT production and consumption patterns in Mexico during the last 20 years are described and compared with those in the United States. In spite of the restrictions on DDT use in antimalaria campaigns in Mexico, use of DDT is still higher than in other Latin American countries. We analyzed information from published studies to determine accumulated levels of this insecticide in blood, adipose tissue, and breast milk samples from Mexican women. Current lipid-adjusted DDE levels from women living in Mexico City are 6.66 ppb in mammary adipose tissue and 0.594 ppm in total breast milk. Finally, the methodological limitations of existing epidemiological studies on DDT exposure and breast cancer are discussed. We conclude that DDT use in Mexico is a public health problem, and suggest two solutions: identification of alternatives for the control of malaria and educational intervention to reduce DDT exposure. We also recommend strengthening epidemiological studies to evaluate the association between accumulated DDT levels in adipose tissue and breast cancer incidence among Mexican women.