00000000Mexico and Puerto Rico are but two examples of the changing epidemiologic patterns of dengue observed in the Americas in recent years. Limited surveillance data from other countries in Central America and South America, Hispaniola and some of the Lesser Antilles islands suggest similar changes. Moreover, the distribution of epidemic dengue is expanding rapidly. Just since 1986, major epidemics have occurred in several countries of areas that had been free of dengue for over 50 years. These include the Rio de Janiero area of Brazil (1986), Bolivia (1987 - 1988), Paraguay (1988) and Ecuador (1988). Additionally, in 1987 Venezuela experienced its first dengue outbreak in ten years, and after an absence of 35 years, the United States (Texas) documented indigenous transmission twice in the 1980s (in 1980 and 1986).

00000000In summary, several factors are responsible for the increased dengue incidence and the emergence of DHF/DSS in the American region. First, there has been a near complete breakdown in mosquito control in most countries. As noted above, A. aegypti has reinvaded nearly every country where it previously occurred and densities are higher. Second, increased and more rapid air travel has led to increased movement of dengue viruses within the region as well as frequent introduction of viruses from Asia and Africa. Finally, ecologic conditions have been created in tropical American cities that allow coexistence of multiple dengue virus serotypes. Prospects for changing these conditions in the near future are not good. Thus, DHF/DSS has become widespread and endemic in the Americas (Figure 2), and unless effective mosquito control programmes are implemented immediately, more frequent and larger epidemics of dengue and DHF/DSS can be expected in the future.