In the last 20 years, the incidence of dengue and its more severe, often lethal, formùdengue hemorrhagic fever (DHF) – has increased dramatically, especially in the tropical regions of the world. During the 1960s, dengue typically averaged about 30,000 cases per year [1]. Some 30 years later, though, in 1995, 592,000 cases of dengue were reported, and the true number of people afflicted is believed to be several fold higher [2]. The World Health Organization (WHO) estimates that 20 million cases occur each year, requiring 500,000 hospitalizations [3], and researchers estimate that 2.5 billion people live in urban tropical centers, placing them at risk of contracting the disease [4].
Also known as “break-bone” fever, dengue is the Swahili term for “a sudden overtaking by a spirit.” Caused by four distinct virus serotypes, the disease’s symptoms include fever, severe headaches, and disabling muscle and joint pain. Although classical dengue is relatively benign, the more serious hemorrhagic form causes breathing difficulties and bleeding from the nose, mouth, and gums [5]. Multiple infections are possible because immunity to one virus serotype does not provide immunity to the others. In fact, previous infection from one dengue serotype or a sequence of infections can contribute to the risk of contracting the more severe DHF [6]. Approximately 5 percent of all DHF cases are fatal, mostly among children [7]. Although dengue is still rarely lethal, its contribution to disease and ill health, especially among young children, should make dengue control a primary public health concern.
The reemergence of dengue as a public health threat illustrates how human-directed changes in the environment can influence the patterns of infectious disease. Although the various factors responsible for this worldwide increase in dengue are not fully understood, it is believed that rapid urbanization, the wide use of nonbiodegradable plastic packaging and cellophane, increased travel and trade, and the lack of effective mosquito control efforts contribute in important ways to the spread of the disease [8].
Demographic changes – in particular, rapid, unplanned urbanization – have resulted in conditions that encourage the spread of dengue. The two primary mosquito vectors of dengue, Aedes aegypti and Aedes albopictus, have adapted from their natural forest environs (where they breed in tree holes containing rainwater) to the urban environment (where they breed in pots, pitchers, water cans, drains, bottles, and discarded tires). This fact makes dengue particularly troublesome in cities of the developing world, where between one third and two thirds of solid waste is not collected, but left on streets, in drains, or dumped in open landfills [9]. In addition to waste usage problems, crowding, inadequate water and sanitation systems, and poor housing conditions can further facilitate the spread of the disease [10].
| Populations at potential risk of Dengue Fever |
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References and notes
1. Thomas P. Monath, “Dengue: The Risk to Developed and Developing Countries,” Proceedings of the National Academy of Sciences, Vol. 91 (March 1994), p. 2397.
2. World Health Organization (WHO), The World Health Report 1996: Fighting Disease, Fostering Development (WHO, Geneva, 1996), p. 24.
3. Ibid., p. 48.
4. Duane J. Gubler and Gary G. Clark, “Community Involvement in the Control of Aedes aegypti ” Acta Tropica, Vol. 61 (1996), p. 170.
5. Op cit. 2, p. 48.
6. Duane J. Gubler, “Vigilancia Activa Del Dengue y de la Fiebre hemorrágica del Dengue,” Boletín de la Oficina Sanitaria Panamericana, Vol. 107 (1989), pp. 22-30, cited in Baltasar Briseño-García et al., “Potential Risk for Dengue Hemorrhagic Fever: The Isolation of Serotype Dengue-3 in Mexico,” Emerging Infectious Diseases, Vol. 2, No. 2 (April-June 1996).
7. Duane J. Gubler and Gary G. Clark, “Dengue/Dengue Hemorrhagic Fever: The Emergence of a Global Health Problem,” Emerging Infectious Diseases, Vol. 1, No. 2 (1995), pp. 55-57.
8. Op. cit. 4.
9. World Resources Institute in collaboration with the United Nations Environment Programme, the United Nations Development Programme, and The World Bank, World Resources 1996-97: The Urban Environment (Oxford University Press, New York, 1996), pp. 23 and 70.
10. Duane J. Gubler and Gary G. Clark, “Community-Based Integrated Control of Aedes aegypti: A Brief Overview of Current Programs,” American Journal of Tropical Medicine and Hygiene, Vol. 50, No. 6 (1994), p. 50.
