00000000The expanding distribution of A. aegypti in the 1970s coincided with increased movement of dengue viruses both within and into the region, primarily by airplane travellerrs. The result was a constant increase in the amount of dengue transmission in the American region caused by multiple virus serotypes. In the past, most epidemics were caused by one, or occasionally two, dengue serotypes, but multiple serotypes are now endemic in most countries of the region. This has resulted in increased frequency of epidemic activity (Table 1) and the emergence of dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS0 as a major public health problem in the Americas.

00000000The evolving disease pattern in the Americas since the late 1970s is nearly identical to that which occurred in South-East Asia 30 years ago (Table 2)(10). Expanded distribution and increased densities of A. aegypti occurred during and after World War II in Asia, and after failure of the A. aegypti eradication programme in the Americas. In both regions this was followed by increased transmission of multiple dengue virus serotypes resulting in hyperendemicity in many countries. In every country in South-East Asia where epidemic DHF/DSS became a major public health problem, the disease first appeared sporadically for several years, ultimately culminating in a major epidemic. Most of those countries subsequently developed a continuing cycle of epidemic DHF/DSS at three-to-four-year intervals with epidemics becoming progressively larger.

Table 2. Similarities in the sequence of events leading to epidemic dengue haemorrhagic fever in South-East Asia and the Americas

00000000In the Americas, the first major epidemic of DHF/DSS occurred in 1981 in Cuba(11). Moreover, sporadic cases of laboratory confirmed severe and fatal haemorrhagic disease associated with dengue infection have been reported in Mexico, El Salvador, Nicaragua, Jamaica, the Dominican Republic, Puerto Rico, St. Lucia, Aruba, Brazil, Surinam, Colombia and the United States (imported), while other countries such as Curacao and Haiti have reported cases that were clinically compatible with DHF, but were not laboratory confirmed (Table 3). It will be noted that most of the haemorrhagic disease has occurred in recent years. Thus, with increased incidence, there has been increased DHF/DSS in most countries where dengue has become hyperendemic. Available data suggests that the dengue disease pattern evolved in the Americas in the 1980s as it did in Asia 30 years ago. It is not yet known whether DHF/DSS will become a major public health problem in the Americas as it is in Asia.