Academic journal article Bulletin of the World Health Organization

Eco-Bio-Social Determinants of Dengue Vector Breeding: A Multicountry Study in Urban and Periurban Asia /Determinants Ecologiques, Biologiques et Sociaux Conditionnant la Reproduction Des Vecteurs De la Dengue : Etude Menee En Zone Urbaine et Periurbaine Dans Plusieurs Pays d'Asie/ Determinantes Ecobiosociales De la Reproduccion del Vector del Dengue: Estudio Multipais En Zonas Urbanas Y Semiurbanas De Asia

Academic journal article Bulletin of the World Health Organization

Eco-Bio-Social Determinants of Dengue Vector Breeding: A Multicountry Study in Urban and Periurban Asia /Determinants Ecologiques, Biologiques et Sociaux Conditionnant la Reproduction Des Vecteurs De la Dengue : Etude Menee En Zone Urbaine et Periurbaine Dans Plusieurs Pays d'Asie/ Determinantes Ecobiosociales De la Reproduccion del Vector del Dengue: Estudio Multipais En Zonas Urbanas Y Semiurbanas De Asia

Article excerpt

Introduction

Dengue, which is the fastest re-emerging arboviral disease in the world, imposes a heavy economic and health burden on countries, families and individual patients. (1,2) In the absence of an effective drug or vaccine, the only strategic options presently available are case management to prevent death and vector control to reduce viral transmission. However, large dengue outbreaks continue to occur every year and the disease is extending to new geographical areas. (3) Integrated vector management can reduce vector densities considerably, (4) but the results of vector control programmes are often far from ideal. (5) Routine interventions against the immature stages of the rector have proved ineffective for a long time, (6) while the results of vertical interventions are often transient. (7) Several user-friendly dengue vector control tools and approaches have become available, (8-12) but questions remain as to their effectiveness, alone or in combination, and their cost-effective delivery by public health services and the private health sector.

Most research on dengue vectors focuses on the biological and behavioural characteristics of the insect, (13,14) the efficacy and cost of specific interventions, (15) and different delivery strategies for vector management. (16) Although systematic literature reviews and meta-analyses of the results of these "single focus" studies can provide a comprehensive picture of the mix of interventions needed for successful vector control, (5,17) this approach has several limitations. Comparing results is difficult because studies employ different methods and focus on different factors. Furthermore, efficacy trials and effectiveness studies on dengue vector interventions often have questionable outcome measurements. Larval indices (e.g. the house index, the container index, the Breteau index), (18) which are based on the presence or absence of immature forms of the vector in water containers, were useful in eradicating Aedes aegypti from the American continent in the late 1940s. (19) However, they are inappropriate for estimating vector densities (20) and of limited use for assessing dengue transmission risk. (21) Work by Focks et al. (22) and subsequent multicentre studies (23-25) have reconfirmed the usefulness of pupal surveys to identify the types of containers that are epidemiologically important and to estimate adult vector abundance. A further limitation is that dengue vector studies usually focus either on house holds or on defined public spaces (26,27) and therefore lack the analysis of vector production in defined geographical areas (spatial focus). Finally, even though the factors influencing dengue vector densities and ultimately viral" transmission are ecological, biological and social (eco-bio-social), as illustrated in Fig. 1, multivariate analyses comprising a combination of these factors have, to our knowledge, not been conducted on a large scale.

[FIGURE 1 OMITTED]

For all the reasons cited, we performed a multicountry study focused on geographical areas, including private and commercial premises as well as public spaces and buildings, in six large and middle-sized Asian cities. Its purpose was to answer the following research questions: (i) What is the relative importance of domestic, peridomestic and public spaces for the production of dengue vectors? (ii) What ecological, biological and social factors determine dengue vector densities and contribute to viral transmission? (iii) What are the main implications for vector control services?

Methods

Study period and sites

The study was designed in Bangkok in 2006 during a protocol development workshop that was attended by all principal investigators. It was to be conducted in two phases: Phase 1 was the situational analysis that is described in this paper (field studies were carried out in 2007-2008 and the data were analysed in 2008-2009); phase 2 was designed as an intervention study in six sites, with some intervention and some control neighbourhoods and a cluster randomized study design in three sites and a case study design in the other three sites (phase 2 studies started in 2009). …

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