SPECIAL EDITORIAL EDITORIAL ESPECIAL
Dengue fever and the urban environment
Roberto de Andrade Medronho
Núcleo de Estudos de Saúde Coletiva/UFRJ
The introduction of dengue virus serotype 3 in december, 2001 led to the largest and most severe epidemic of the disease in Brazil, with more than 1.2 million cases reported in 2001 and 2002, in addition to the concurrent circulation of serotypes 1 and 2. After this period, the endemic-epidemic process remained mainly in large metropolitan regions of the country, also contributing to the spread of the disease to other cities. Several features contributed to the spread of the Aedes aegypti to these regions. The disorderly urbanization process, generating high demographic density regions with severe deficiencies in water supply and urban sanitation, the intense interchange of people between urban areas, and fundamentally, the inefficiency in fighting the vector made controlling dengue an arduous task.
The great complexity of this anthropic environment makes it essential to rethink the disease control strategy. The mechanism of production of the disease requires the adoption of integrated policies in several sectors, and not only health. One should bear in mind that although dengue fever is clearly related to the health sector, it is not a specific problem of this sector. Moreover, the policies to fight the disease must extrapolate the municipal scope in these large metropolises. In fact, the integration of actions to control the vector should begin within health departments themselves, given that in many of them disease surveillance is not integrated to entomology surveillance. An appropriate initiative could be the integration of the Yellow Fever and Dengue Information System (Sistema de Informações de Febre Amarela and Dengue SISFAD) with the National System for Reportable Conditions (Sistema de Informações de Agravos de Notificação SINAN). This could help the adoption of measures of containment by reporting suspect cases opportunely.
Today, there are technologies for stratifying municipalities according to risk areas, with the definition of specific indicators (entomological, epidemiological and socio-environmental) to improve actions. In this fashion, the utilization of geographical information systems may become a powerful tool to support dengue prevention and control actions.
So far, the only controllable element of dengue's epidemiological chain is its vector. In this sense, it is necessary to invest in research to study in further detail the behavior of the Aedes aegypti. The knowledge of the productivity of the various types of breeding sites in the urban environment, of environmental conditioning factors, and of the presence and dynamics of the dengue virus in mosquitoes is very relevant to understand the disease transmission dynamics.
The strategies to control the vector try to prioritize locations with a large number of breeding sites with immature forms of the mosquito. An issue that is currently being discussed is the productivity of foci. Small foci do not seem to be very important in the production of the adult form and, consequently, in disease transmission. Therefore, there may be other sites with a large number of small foci that tend to have low productivity of adult forms of the vector. On the other hand, a single large focus may have high productivity and thus also contribute to the generation of small foci of the mosquito. Educational actions could be directed preferably toward large foci. In this sense, it is critical to analyze the productivity of Aedes aegypti breeding sites, by calculating the emergence of adult females, taking into consideration the number of pupas collected in recipients. The estimate of productivity could define risk areas more accurately and contribute to optimize vector control actions.
The Ministry of Health has taken an appropriate initiative to provide access to information on the vector through the quick identification of the building infestation index, which should be maintained and expanded to other municipalities. These data should be made available by the Ministry of Health with the necessary break-down in order to acknowledge rates by site, and not only municipal averages that eventually tone down differences between municipalities.
Up to now, unfortunately, the modulation of the epidemic process has been a function of group immunity and not of efficient vector control. Therefore, with the circulation of serotype 4 in nearby or even border countries such as Venezuela, there is a risk of re-introduction of this serotype, which allied to a susceptible population and high vector density would be the ideal ingredients for a new explosive epidemic process. In this scenario, the key for not having an explosive epidemic is efficient vector control. There is still time, although political will seems to lack in many instances.
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