Fig. 1. Aedes aegypti distribution in the Americas: 1930s, 1970 and 2001. disease of humans, occurring in tropical countries of the world where> 2.5 billion people are at risk of infection [1, 3, 7](Fig. 2). More than 100 tropical countries have endemic dengue virus infections, and DHF has been documented in> 60 of these countries [8]. Surveillance for DF/DHF is poor in most countries, and in the past has focused primarily on DHF [3]; the number of DF cases that occur each year can therefore only be estimated. In 1998, however, major epidemics occurred throughout Asia and the Americas, with> 1.2 million cases of DF/DHF reported to the WHO. Global reports of DHF have increased on average by fivefold in the past 20 years (Fig. 3). At the beginning of the 21st century it is estimated that between 50 and 100 million cases of DF and several hundred thousand cases of DHF occur each year, depending on the epidemic activity. The case fatality rate (CFR) varies among countries, but can be as high as 10–15% in some and< 1% in others.

The majority of DHF cases are reported from Asia where the disease has affected most countries, and is a leading cause of hospitalization and death among children. In the American tropics, DHF was a rare disease before 1981. Since that time, epidemic DF/DHF has become one of the most important public health problems of the region. The only tropical region of the world where it is not considered a major problem is Africa, where other disease problems are overwhelming by comparison. The real public health impact of DF/DHF occurs during epidemics of this disease. Because surveillance is poor, the early stages of epidemic transmission are usually not detected, with cases grossly under-reported until the epidemic is recognized as dengue, which is usually near peak transmission; it then becomes grossly over reported [9]. Emergency mosquito control is usually initiated at that time, but these efforts are usually misdirected, and are too little and too late to have any impact on the epidemic [9]. Thus, the public health impact of epidemic DF/DHF is amplified because there is poor surveillance, no public health planning and no properly implemented emergency response plans.