The global prevalence of dengue has grown dramatically in recent
decades. The disease is now endemic in more than 100 countries in Africa, the
Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific
(see Table 1). South-East Asia and the Western Pacific are most seriously
affected. Before 1970 only nine countries had experienced DHF epidemics, a
number which had increased more than four-fold by 1995. Some 2500 million people
- two fifths of the world's population - are now at risk from dengue. WHO
currently estimates there may be 50 million cases of dengue infection worldwide
every year. In 1998 alone, there were more than 616,000 cases of dengue in the
Americas, of which 11,000 cases were DHF. This is greater than double the number
of dengue cases which were recorded in the same region in 1995. Not only is the
number of cases increasing as the disease is spreading to new areas, but
explosive outbreaks are occurring. In Brazil nearly 475,000 cases were reported
between January and October 1998 more than were reported from the entire
continent in previous years.
Some other statistics:
· During epidemics
of dengue, attack rates among susceptibles are often 40 50%, but may
reach 80 90%.
· An estimated 500 000 cases of
DHF require hospitalisation each year, of whom a very large proportion are
children and roughly 5% die.
· Without proper treatment, DHF
case fatality rates can exceed 20%. With modern intensive supportive therapy,
can be reduced to less than 1%.
The spread of dengue is attributed to expanding geographic
distribution of the four dengue viruses and of their mosquito vectors, the most
important of which is the predominantly urban species Aedes aegypti. A
rapid rise in urban populations is bringing ever greater numbers of people into
contact with this vector, especially in areas which are favourable for mosquito
breeding e.g., where household water storage is common and where solid waste
disposal services are