Dengue is widespread throughout the tropics, with risk factors influenced by local spatial variations of rainfall, temperature, relative humidity, degree of urbanization and quality of vector control services in urban areas. Before 1970, only nine countries had experienced severe dengue epidemics. Today, the disease is endemic in more than 100 countries in WHO’s African, Americas, Eastern Mediterranean, South-East Asia and Western Pacific regions; the Americas, South-East Asia and Western Pacific regions are the most seriously affected.
Member States in three WHO regions regularly report the annual number of cases to the Secretariat. Figure 1 shows the number of dengue cases (suspected or confirmed) notified to WHO since 1990.
The actual numbers of dengue cases are underreported and many cases are misclassified. One recent (2013) estimate indicates that 390 million dengue infections occur every year (95% credible interval 284–528 million), of which 96 million (67–136 million) manifest clinically (with any severity of disease).1 Another (2012) study, of the prevalence of dengue, estimates that 3.9 billion people in 128 countries are at risk of infection with dengue viruses.2
While these figures are estimates – and should therefore be interpreted with the known limitations that accompany modelling studies – they highlight the staggering epidemiological and economic burden that endemic countries are facing. There is a large discrepancy between the dengue burden estimated by academic groups and the dengue burden notified to WHO. The reasons for this include lack of resources and capacity to survey dengue effectively, and the fact that many countries report only laboratory-confirmed cases, which represent only a small majority of the total number of dengue cases recorded and reported. Importantly, as shown in Figure 2, WHO does not receive dengue case notifications from all affected countries. No cases are currently reported from Sub-saharan Africa (AFRO) or the Eastern Mediterranean Region (EMRO), which are estimated to contribute significantly to the global burden of dengue.
To enrich the use of data collected and notified by governments, WHO will publish dengue data on the WHO website and prepare the first Global Dengue Report at the end of 2017.
1 Bhatt S, Gething PW, Brady OJ, Messina JP, Farlow AW, Moyes CL et.al. The global distribution and burden of dengue. Nature. 2013;496:504–7. doi:10.1038/nature12060.
2 Brady OJ, Gething PW, Bhatt S, Messina JP, Brownstein JS, Hoen AG et al. Refining the global spatial limits of dengue virus transmission by evidence-based consensus. PLoS Negl Trop Dis. 2012;6:e1760. doi:10.1371/journal.pntd.0001760.