**2. Geographic distribution**

It is scientifically accepted that dengue viruses originated in monkeys and jumped to humans in Africa or Southeast Asia between 100 and 800 years ago. Dengue fever remained geographically

**Figure 1.** Distribution of dengue worldwide (taken from www.who.int/denguecontrol/ epidemiology/).

restricted till 1950s. But due to the Second World War, transport of *Aedes* mosquitoes happened around the world which played a crucial role in the dissemination of the viruses. Now, approximately 2.5 billion people live in areas where there is a risk of dengue transmission [9–12].

During 1850s, first case of dengue was documented in the Philippines and Thailand. Later, after 1980s large number of cases began to appear in the Caribbean and Latin America. Today, Dengue is endemic in at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. Dengue fever is reported to prevail in 26 states [13–15]. DENV-2 was the predominant serotype in dengue outbreaks that occurred before 2000 but DENV-3 was the predominant serotype between 2000 and 2009. After 2010, DENV-1 dominated global dengue outbreaks, and DENV-4 was the least frequently identified serotype [16, 17]. The geographical distribution of dengue with respect to countries has been shown in **Figure 1** which explains the current prevalence of this disease around the world [11].
