Recent Changes in Epidemiology

00000000Two countries that exemplify the changes in epidemiology that have led to the current problem in the Americas illustrate what has happened in the region as a whole.Mexico eradicated Aedes aegypti in the 1960s and as a consequence had no dengue transmission during the 1960s and early 1970s and the first cases of dengue were subsequently reported from the southern state of Chiapas, in 1978. By the nest year, however, dengue transmission was reported in eight states, and over the nest sever years, outbreaks were reported in 24 states (Table 4). Moreover, Mexico evolved from a country of low endemicity with only a single dengue virus serotype (DEN-1) in 1978 to a hyperendemic area with three serotypes (DEN-1, -2 and -4) transmitted from 1983 to the present. The first cases of haemorrhagic disease associated with dengue in Mexico occurred in 1983 and were associated with a DEN-1 epidemic. In 1984, an outbreak of DEN-4 occurred in Merida, Yucatan, during which nine cases of haemorrhagic disease (four fatal) were

Table 3. Occurrence of dengue haemorrhagic fever
in the Americas, by year

*Predominant virus serotype listed first.