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Dengue has become a major public health problem in intertropical areas where an estimated 60 million new cases and 30,000 deaths occur annually. The causative agent is transmitted by the bite of Aedes mosquitoes which are the main and perhaps only reservoir of the disease. In addition to increasing incidence clinical manifestations of dengue have changed over the last 40 years. An increasing number of reported cases involve hemorrhage, shock, and other severe complications especially in Southeast Asia, northern regions of South America, and the Caribbean. Some of the same factors responsible for these changes are probably implicated in the development of other emerging viral diseases.

The epidemiology of dengue fever is changing dramatically. The worldwide incidence is rising and clinical symptoms are worsening. Reports describing forms associated with hemorrhage or shock syndrome involving both children and adults are increasingly frequent in regions beyond Southeast Asia where the first cases were observed. Many mechanisms could be implicated in these changes including modifications of the virus, host, vector, or socioeconomic factors. Since no current model allows laboratory analysis of these mechanisms, observation of epidemics is still a major source of data. The findings of well conducted epidemiological studies allow not only assessment of morbidity and mortality in endemic areas and early detection of epidemic outbreaks but also evaluation of socioeconomic impact and effectiveness of control measures. Surveillance techniques must be chosen in function of prevailing local conditions. To ensure reliable results studies should be carried out in collaboration with an international network and a simple and accurate method of disease identification should be used.

The situation of dengue in the world can be summarized as follows: 2,5 billions persons at risk, 60 millions cases per year, and 30 000 deaths per year. The four dengue serotypes, DEN-1, DEN-2, DEN-3 and DEN-4 are nearly human-specific. Clinical symptoms of dengue vary from unapparent infection, mild febrile manifestations to hemorrhagic forms with or without shock syndrome. Dengue viruses are transmitted by Aedes mosquitoes, the most important vectors being Aedes aegypti and Aedes albopictus. The epidemiology of the disease can be divided into endemo-epidemic situations occurring in South-East Asia, and epidemic situations found in Pacific islands, Africa and Tropical America. Maintenance of dengue is supported by an increasing demography, uncontrolled urbanization and climatic conditions favorable to the vectors. Spread of dengue is primarily caused by modern transportation means, especially the aircraft. The geographical distribution of dengue is pantropical, except for Madagascar and some african regions. Because no vaccine and no specific treatment actually exist against dengue viruses, mosquito control is the only way to reduce the incidence of dengue around the world. However, the evolution of the dengue situation is not satisfactory.