Book Review
Dengue Prevention and Control Weekly Epidemiological Record 2002, 76(29): 217-218
Dengue is the most common and widespread arthropod-borne viral infection in the world. There are 4 distinct virus serotypes, each capable of producing a wide spectrum of signs and symptoms that characterize dengue fever, ranging from sub clinical infection, to a debilitating but selflimiting illness with symptoms resembling influenza, to severe disease known as dengue haemorrhagic fever. Without proper
hospital care, the latter can lead to clinical shock and death in less than 24 hours The geographical spread, incidence and severity of dengue fever and dengue haemorrhagic fever are increasing in the Americas, the Eastern Mediterranean, SouthEast Asia and the Western Pacific Regions (Figure).
Figure: Dengue, 2001
Countries/areas reporting dengue cases
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Before 1970, only 9 countries had experienced dengue haemorrhagic fever. Since then, the number has increased more than fourfold and continues to rise. Some 2.5-3 billion people live in areas where dengue viruses can be transmitted. A pandemic in 1998, in which 1.2 million cases of dengue fever and dengue haemorrhagic fever were reported from 56 countries, was unprecedented. Preliminary data for 2001 indicate a situation of comparable magnitude. However, only a small proportion of cases are reported to WHO; it is estimated that each year 50 million infections occur, with 500,000 cases of dengue haemorrhagic fever and at least 12,000 deaths, mainly among children, although fatalities could be twice as high. Without proper clinical management, case-fatality rates for dengue haemorrhagic fever can exceed 20%. However, with intensive supportive therapy, rates can be reduced to less than 1%. The resurgence of epidemic dengue fever and the emergence of dengue haemorrhagic fever as major public health problems are rooted in the demographic trends and socioeconomic policies of the 20th century. During the past five decades, the population of the world has more than doubled, with the most rapid acceleration taking place in developing countries in the tropics and subtropics where dengue viruses are spread by mosquitoes. Several factors have combined to produce epidemiological conditions that highly favour viral transmission by the main mosquito vector, Aedes aegypti: population growth, ruralurban migration, the inadequacy of basic urban infrastructure (e.g. unreliable water supply, which may lead householders to
collect and store water close to homes) and the huge increase in volume of solid waste resulting from the new habits of consumers, for example, discarded plastic containers and other abandoned items which provide larval habitats in urban areas. The species thrives in intimate association with humans and is also the vector of the virus of urban yellow fever, a vaccine-preventable disease. A secondary vector of dengue virus, Ae. albopictus, which until the late 1970s was geographically limited to parts of Asia, has now become established in Africa, the Americas and Europe. Geographical expansion of this mosquito has been aided particularly by international commercial trade in used tyres which, with accumulated rainwater, are attractive habitats for egglaying females of the species. Its role in the transmission of dengue and potentially also of yellow fever and other arthropod-borne viruses in these new epidemiological settings remains to be determined. The magnitude of the public health problem will continue to grow unless more effective measures are taken to reduce viral transmission. In many countries, health-sector reform poses new challenges for programme delivery, including decentralization and issues of selection, purchase, procurement, use and monitoring of insecticide application. Moreover, few new costeffective chemical pesticides suitable for public health use have been developed in recent years. This problem is particularly acute with regard to larvicides suitable for use in stored water for domestic consumption. Although research on dengue vaccines for public health use is in process, currently the only method for the prevention and control of the disease is vector control. Dengue Bulletin – Vol 26, 2002
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The global strategy enunciated in 19951 recommended the application of integrated vector control measures, with community and intersectoral participation. An informal WHO consultation on strengthening implementation of the global strategy for prevention and control of dengue fever/dengue haemorrhagic fever (Geneva, 18-20 October 1999), the subsequent inclusion of dengue in the disease portfolio of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases in June 2000, and advances in regional strategy formulation in the Americas, South-East Asia and the Western Pacific during the 1990s, have facilitated identification of the following four main priorities: (1) Strengthening epidemiological surveillance for planning and response, including entomological surveillance and the monitoring of key human behaviours (such as inappropriate disposal of discarded household items) that contribute to the availability of mosquito larval habitats. Epidemiological surveillance includes the introduction of DengueNet, a global surveillance system for dengue fever on the Internet. This network includes a database which will be continually updated and which will allow remote data entry in order to 1 Report of the consultation on key issues in dengue vector control toward the operationalization of a global strategy, WHO, Geneva, 6-10 June 1995, document CTD/FIL(DEN)/IC/96.1). Can be obtained on request from the CDS Information Resource Centre, World Health Organization, 1211 Geneva 27, Switzerland; fax: +41 22 791 42 85; email: cdsdoc@who.int)
provide a more comprehensive and current global picture. (2) Reducing the disease burden through: accelerated training and the adoption of WHO standard clinical management guidelines for dengue haemorrhagic fever; improving emergency preparedness and response, and strengthening of national vectorcontrol programmes. (3) Promoting behavioural change through the development and implementation of a package of tools, approaches and guidelines for sustainable prevention and control of vectors at individual, household, community, institutional and political levels. The approaches will also foster intraand intersectoral partnerships for programme implementation. (4) Accelerating the research programme, with emphasis on mechanisms of pathogenesis, transmission dynamics, vaccine development, validation and improvement of existing or new vector-control methods and their application, partnership building, and formulation of guidelines for research in these strategic areas. Given the worsening epidemiological trends, there is evident need to renew or intensify efforts to reduce the public health and economic burdens associated with this epidemic disease. In order to achieve this, the following will be required: the development, application and evaluation of 205
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new and improved tools and strategies for the prevention and control of dengue fever and dengue haemorrhagic fever; increased commitment and additional human and other resources for improved and sustainable prevention and control efforts; building and strengthening the capacity of health systems
for dengue surveillance, laboratory diagnosis and disease management, and active intersectoral partnerships involving international, regional, national and local agencies and nongovernmental organizations.
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