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84 THIRD WHO REPORT ON NEGLECTED TROPICAL DISEASES
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Burden and distribution
Dengue is widespread throughout the tropics, with local spatial variations in risk influenced
strongly by rainfall, temperature and the degree of urbanization. The actual numbers of cases
are underreported and many cases are misclassified. One recent estimate indicates 390 million
dengue infections per year (95% credible interval 284–528 million), of which 96 million (67–136
million) manifest clinically (with any severity of disease) (1). Another study, of the prevalence
of dengue, estimates that 3900 million people, in 128 countries, are at risk of infection with
dengue viruses (2). Member States in three WHO regions regularly report the annual number
of cases to the Secretariat; in 2013, nearly 3 million cases were so reported. Although the full
global burden of the disease is uncertain, its epidemiological patterns are alarming for both
human health and the global economy (Fig. 4.3.1) (3).
Fig. 4.3.1 Distribution of countries or areas at risk of dengue transmission, worldwide, 2014
January isotherm
10 °C
July isotherm
10 °C
Countries or areas at risk of dengue transmission
Not applicable
The contour lines of the January and July isotherms
indicate areas at risk, defined by the geographical limits
of the northern and southern hemispheres for year-round
survival of Aedes aegypti, the principal mosquito vector of dengue viruses
The principal vectors of dengue have continued to silently expand their distribution globally
and are now present in more than 150 countries. Movement of goods (used tyres and plants
with axils) containing dried mosquito eggs have facilitated the vectors’ spread. Both the main
vectors transmit not only dengue virus but also other closely related arboviruses such as
chikungunya and Zika viruses.