The following is an excerpt from a white paper produced by Lars Eisen and Barry Beaty of Colorado State University, Tom Scott of University of California, Davis, and Tom McLean of the Innovative Vector Control Consortium.

 

In this white paper, we highlight:

1. Emerging technologies and novel approaches with potential for making vector control more effective; and
2. New opportunities for vector control targeting the epidemiologically most significant point of contact for dengue virus transmission – – the indoor environment.

We also outline five challenges in vector and dengue control for the research and public health communities in the next 5-yr period.

Emerging technologies

• Mapping technology. The emergence of Geographic Information System (GIS) technology and the rapidly increasing availability of free and at-cost GIS software and cartographic, demographic, socioeconomic, and environmental GIS-based data have revolutionized our capacity to visualize and model spatial vector and disease patterns. In the case of Aedes aegypti and dengue, GIS has provided capacity for: 1) presentation and analysis of spatial and spatiotemporal patterns of risk of exposure to vectors or dengue virus (Morrison et al. 1998); and 2) development of predictive spatial risk models based on associations between GIS-derived data and vector or disease measures (Rotela et al. 2007). Other emerging mapping technologies that can complement GIS software include Google Earth and MS Virtual Earth, which provide free access to satellite imagery (often of stunning quality in urban areas) and a basic set of tools to generate points, lines and polygons.
  
  
• Decision support systems. The purpose of a decision support system (DSS) is to aid and systematize the process of gathering and analyzing information, gaining new insights, generating alternatives and, ultimately, making evidence-based decisions. DSS's have been used extensively in clinical and diagnostic medicine, veterinary medicine and agriculture and forestry pest management, and also have great potential for improving prevention and control of dengue (Eisen and Beaty 2008). Dengue control programs implementing a DSS will benefit from improved logistical capacity for managing and evaluating integrated vector control strategies or, when a vaccine becomes available, integrated vector control – vaccination strategies.
  
  
• Modeling. Quantitative models are needed to account for the complex natural history of dengue and epidemiologically important heterogeneities in its transmission. Simulation models for Ae. aegypti population dynamics and dengue virus transmission (Focks et al. 1993, 1995) can be used as stand–alone products or in a decision support system. They can be used to explore outcomes of specific intervention strategies, or to explore how the level of herd immunity in the human population (natural or enhanced through immunization) will impact operational vector control threshold targets. Recent innovations in software and analytical technology provide an opportunity to refine existing models and to create new models that can inform more effective use of limited resources by identifying strategies and establishing priorities with the greatest probability of success (Morrison et al. 2008).
  
  
• Long-lasting insecticide-treated materials (LL-ITMs). Use of LL-ITMs, which can remain efficacious for >5 years, as bednets for malaria control has been a public health success (N'Guessan et al. 2001) and LL-ITMs in the form of bednets or window curtains now offer great potential for control of other vector-borne diseases commonly transmitted in the home environment such as dengue (Nam et al. 1993, Kroeger et al. 2006, Lenhart et al. 2008). LL-ITMs can potentially protect homes, schools, or other structures where people are exposed to Ae. aegypti for multiple years at low cost. Protection may also extend to other disease vectors or pest insects, including nuisance-biting Culex mosquitoes, thereby making LL-ITMs a broad spectrum public health product. Finally, LL-ITMs can be marketed as consumer products in addition to being distributed to high risk areas, or during dengue outbreaks, by vector control programs.
  
  

Novel approaches

• Development and implementation of adaptive vector and dengue control strategies. Emerging technologies such as GIS, decision support systems and improved models provide new frameworks for development, implementation and evaluation of adaptive vector and dengue control strategies. This provides an opportunity for local and national control programs to jointly develop control strategies that are adapted to local ecologic and epidemiologic conditions while still being accepted and supported by the national program.
  
  
• Use of clinical syndromic surveillance. Use of clinical syndromic surveillance (clinical diagnosis of dengue) rather than laboratory confirmed dengue to trigger vector control response activities can shorten the response time for emergency vector control by several weeks; this approach can be used to rapidly implement vector control and remove local foci of dengue virus transmission within and around the homes of suspected dengue patients.
  
  
• Enhanced control of adults in the indoor environment. The previously described advent of long-lasting insecticide-treated materials (LL-ITMs) offers great potential for vector control targeting the epidemiologically most significant point of contact for dengue virus transmission - - the indoor environment. This approach is predicated upon previous studies demonstrating the potential for using ITMs to reduce vector abundance and dengue virus transmission in southeast Asia (Nam et al. 1993) and the Americas (Kroeger et al. 2006, Lenhart et al. 2008). An effective strategy for enhanced control of adults in the indoor environment could combine use of LL-ITMs with rapid and focused response to clinically diagnosed dengue cases with indoor insecticide application.
  
  
• Targeting of productive containers for control of immatures. Determination of container types that play key roles as producers of pupae, and a subsequent focus on these containers for surveillance and/or control, has received recent interest (Focks and Alexander 2006). This approach is applicable to environmental source reduction as well as biological or chemical control of immatures and may become part of future integrated vector control strategies.
  
  

The overarching challenge for the future is to incorporate these new technologies and novel approaches into operational dengue prevention and control activities as components of more effective integrated vector and dengue management strategies.

Five challenges for the next five years (2009–2013)

Challenge 1). Implementing computer-based technology to enhance vector and dengue control. GIS-based mapping technology already has been incorporated into some vector control programs for entomological or epidemiological surveillance (Ai-leen and Song 2000, Teng 2001). There are a plethora of GIS software available with data processing, spatial analysis and display capabilities ranging from low (HealthMapper) to moderate (SIGEpi) and high (ArcGIS). New mapping technology and modeling techniques also have great potential for use within a dengue decision support system framework (Eisen and Beaty 2008). Imagine, for example, a scenario where clinical data entered at the health clinic level into an electronic case report form distributed as part of a dengue decision support system become instantly accessible to the vector control coordinator who then can initiate a rapid and focused response activity based on passive clinical syndromic surveillance (Figure 1). Our challenge is to incorporate technologies such as GIS, decision support systems and modeling into routine operational control activities.

Work needed to overcome this challenge:
Technology transfer, increase in computer access and development of personnel capacity.

Institutional and resource needs to overcome this challenge:
Enhanced personnel capacity and additional investment in computer hardware and software will be needed in many countries. The cost will depend on existing computer and personnel capacity, selection of software options and access to GIS- and Remote Sensing data. However, the cost is unlikely to be prohibitive considering that the most basic hardware and software options are inexpensive (a $1,500 computer and free software and satellite imagery) and that the investment in mapping technology and personnel development will benefit not only public health programs but also city planning including public transportation, water supply and waste removal.


Figure 1. Rapid response scenario in a Dengue Decision Support System (Pictures by William Cotton).


Challenge 2) Taking back the home from Aedes aegypti and preventing indoor dengue virus transmission. Targeting of Ae. aegypti in the home with insecticide-treated materials offers great potential for prevention and control of dengue (Nam et al. 1993, Kroeger et al. 2006, Lenhart et al. 2008). We now need to operationally test strategies combining the use of LL-ITMs and rapid and focused response to clinically diagnosed dengue cases with indoor insecticide application to take back the home from Ae. aegypti and to prevent indoor dengue virus transmission.

Work needed to overcome this challenge:
Operational evaluation of the proposed strategy, including determination of both entomological and epidemiological outcomes, is urgently needed. This should be done in multiple dengue-endemic areas with different types of housing and ideally include both the home environment and schools. The strategy also should be evaluated as an integrated vector management strategy together with source reduction.

Institutional and resource needs to overcome this challenge:
Meeting this challenge requires operational research involving academic and public health partners. Financial resources needed are in the range of $600,000 per year and site.

Challenge 3) Developing and operationally characterizing new insecticides, formulations and delivery systems. Along with reduction in mosquito development sites and improved living conditions, insecticides will remain the front line of control of Ae. aegypti for the foreseeable future. No new public health insecticides for adult mosquitoes have been developed in more than 30 years and the number of insecticides available for mosquito control is severely limited. Numerous studies have documented resistance of Ae. aegypti to commonly used insecticides, potentially removing them from the armamentarium used by vector control programs.

Work needed to overcome this challenge:
This challenge is being addressed through the efforts of the IVCC to partner with industry to develop new insecticides and formulations and improved delivery systems (Hemingway et al. 2006). In the next five years, we need to operationally characterize these formulations and delivery systems in terms of efficacy and impact on insecticide resistance.

Institutional and resource needs to overcome this challenge:
Meeting this challenge requires continued partnerships between industry (development) and academic and public health institutions (operational evaluation including entomological and epidemiological outcomes). Financial resources needed to support these activities are in the range of $30,000,000-50,000,000/yr for development (including malaria and other mosquito-borne diseases) and $600,000 per year and site included in the operational evaluation.

Challenge 4) Developing improved capacity for monitoring and mitigation of insecticide resistance. Routine operational testing for insecticide resistance in Ae. aegypti is still lacking in many dengue-endemic areas and positive examples of evidence-based insecticide resistance management (IRM) schemes are scarce. Development of nationwide insecticide resistance surveillance programs are needed to ensure judicious and efficacious use of insecticides to combat Ae. aegypti. This needs to be combined with IRM schemes that outline strategies for mitigating insecticide resistance through temporal rotational or spatially mosaic insecticide application schemes (Coleman and Hemingway 2007).

Work needed to overcome this challenge:
Research is needed to address the question of how laboratory-based data from genetic assays, biochemical assays, or bioassays should be used to guide operational decisions on insecticide resistance management. Development of clear guidelines for this is crucial because changes in insecticide use can have both logistical and political ramifications. Improved capacity for implementation and, especially, monitoring of insecticide resistance surveillance and management schemes can be achieved through use of decision support systems (Coleman and Hemingway 2007, Eisen and Beaty 2008).

Institutional and resource needs to overcome this challenge:
Meeting this challenge requires both operational research and development of capacity for insecticide resistance monitoring. Financial resources needed to support these activities are in the range of $2,000,000/yr for research and $500,000 per year and country for development of capacity for insecticide resistance monitoring.

Challenge 5) Catalyzing a discussion of resource allocation and the need for paradigm shifts in vector and dengue control. Because new technologies have emerged and novel approaches to vector and dengue control have been developed over the last decade, vector control programs need to critically assess their current allocation of resources between different activities (e.g., proactive vector control through community-based source reduction, vector surveillance using larval indices, disease surveillance, reactive emergency vector control implemented through vehicle-based ULV spraying) and determine if some of these resources should be shifted to use of new technology or novel approaches. Downstream this needs to be accompanied by operational evaluation of both the implementation cost and efficacy of different activity combinations. Unless additional resources are made available, paradigm shifts in vector and dengue control will likely lead to the demise of some currently used methodologies.

Work needed to overcome this challenge:
Vector control programs need to critically assess their resource allocation schemes and determine which current activities should be retained and which should be replaced. To catalyze the type of discussion needed to meet this challenge we propose the following paradigm shift in vector control resource allocation: funds currently used for vehicle-based ULV spraying should be re-allocated to vector control specifically targeting the epidemiologically most significant point of contact for dengue virus transmission - - the indoor environment, especially the home.

Institutional and resource needs to overcome this challenge:
Resource needs to overcome this challenge include funding for a series of international workshops ($100,000 per workshop) including academics and public health stakeholders representing local as well as national control programs.

References

Ai-leen,G. T., and R. J. Song. 2000. The use of GIS in ovitrap monitoring for dengue control in Singapore. Dengue Bulletin 24:110-116.

Coleman, M., and J. Hemingway. 2007. Insecticide resistance monitoring and evaluation in disease transmitting mosquitoes. Journal of Pesticide Science 32:69-76.

Eisen, L., and B. J. Beaty. 2008. Innovative decision support and vector control approaches to control dengue, pp. 150-161. In Institute of Medicine report on �Vector-Borne Diseases - Understanding the Environmental, Human Health, & Ecological Connections". The National Academies Press, Washington, D.C.

Focks, D. A., D. G. Haile, E. Daniels, and G. A. Mount. 1993b. Dynamic life table model for Aedes aegypti (Diptera: Culicidae): Simulation results and validation. Journal of Medical Entomology 30:1018-1028.

Focks, D. A., E. Daniels, D. G. Haile, and J. E. Keesling. 1995. A simulation model of the epidemiology of urban dengue fever: Literature analysis, model development, preliminary validation, and samples of simulation results. American Journal of Tropical Medicine and Hygiene 53:489-506.

Focks, D. A., and N. Alexander N. 2006. A multi-country study on the methodology for surveys of Aedes aegypti pupal productivity: Findings and recommendations. Geneva, Switzerland: World Health Organization.

Hemingway, J., B. J. Beaty, M. Rowland, T. W. Scott, and B. L. Sharp. 2006. The Innovative Vector Control Consortium: Improved control of mosquito-borne diseases. Parasitology Today 22:308-312.

Kroeger, A., A. Lenhart, M. Ochoa, E. Villegas, M. Levy, N. Alexander, and P. J. McCall. 2006. Effective control of dengue vectors with curtains and water container covers treated with insecticide in Mexico and Venezuela: Cluster randomised trials. British Medical Journal 332:1247-1252.

Lenhart, A., N. Orelus, R. Maskill, N. Alexander, T. Streit, and, P. J. McCall. 2008. Insecticide-treated bednets to control dengue vectors: Preliminary evidence from a controlled trial in Haiti. Tropical Medicine and International Health 13:56-67.

Morrison, A. C., A. Getis, M. Santiago, J. G. Rigau-Perez, and P. Reiter. 1998. Exploratory space-time analysis of reported dengue cases during an outbreak in Florida, Puerto Rico, 1991-1992. American Journal of Tropical Medicine and Hygiene 58:287-298.

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N�Guessan, R., F. Darriet, J. M. Doannio, F. Chandre, and P. Carnevale. 2001. Olyset Net� efficacy against pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus after 3 years' field use in C�te d�Ivoire. Medical and Veterinary Entomology 15:97-104.

Rotela, C., F. Fouque, M. Lamfri, P. Sabatier, V. Introini, M. Zaidenberg, and C. Scavuzzo. 2007. Space�time analysis of the dengue spreading dynamics in the 2004 Tartagal outbreak, Northern Argentina. Acta Tropica 103:1-13.

Teng,T. B. 2001. New initiatives in dengue control in Singapore. Dengue Bulletin 25:1-6.