**3. The vector**

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

**1. Historical background**

4 Dengue Fever - a Resilient Threat in the Face of Innovation

**2. Geographic distribution**

The word "dengue" is known to be derived from Swahili language "ki denga pepo", which illustrates the meaning as "sudden cramp like seizure". The signs and indications that are suggestive of this viral disease can be tracked back to Chinese Chin Dynasty (265–420 AD) where this infection was believed to be a type of water poison and reported to be linked with insects and water [1]. Some of the historical accounts for dengue fever states that about 500–600 years ago, it appeared from Africa while the first and foremost outbreak of this deadly disease reached other parts of world in 1780s [2]. The detection and isolation of dengue virus date backed to the World War II and it was documented in Japan for the first time in 1942 [3]. Dengue-like symptoms have been reported in early Chinese manuscripts which can be traced back to 992 and to 1600s in the West Indies [4]. In another report, Benjamin Rush observed the first detailed symptoms of dengue shock syndrome (now severe dengue) in 1780 during an outbreak in Philadelphia near Delaware River [5]. Similar disease symptoms were observed in North America along Atlantic coast during eighteenth–nineteenth centuries, on the Caribbean Islands and the Mississippi basin [6]. Bancroft reported for the first time that *Aedes aegypti* mosquito is vector of dengue virus [7]. However, modern research about dengue virus was not started until 1943–1944. For the first time culturing and isolation of this virus was performed from suckling mice brain [8].

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 Dengue virus spreads due to infected females of genus *Aedes*, significantly form *Aedes aegypti* and *Aedes albopictus*. There has been a serious concern amid public health departments. In newly invaded countries, *Aedes albopictus* would cause severe epidemics of arbovirus diseases (it is considered as a competent vector transmitting about 22 arboviruses), especially all four serotypes of dengue; however generally it is transmitted by *Aedes aegypti*. *Aedes albopictus* persists to spread, taking the place of *Aedes aegypti* in some areas. [18] *Aedes albopictus* might serve as a maintenance vector of dengue in non-urban areas of Pacific islands and Southeast Asia. *Aedes albopictus* is not considered an imperative urban dengue vector, but in a few countries where *Aedes aegypti* is not present, that is, the Seychelles, parts of China, Japan and Hawaii [18]. The biting females of *Aedes albopictus* were discovered firstly in 1999, in Southern Cameroon; it provoked survey in 2000 and then adults as well as breeding populations were identified in five major cities of the country mainly breeding in old tires imported from Nigeria and USA which were infested with the mosquitoes [19].

*Aedes* is best known vectors of dengue fever and yellow fever. Some species of *Aedes* are also vectors of viral disease and filariasis [20]. Several serotypes of the dengue virus are carried to human beings via the bites of *Aedes* mosquitoes infected with dengue virus. *Aedes aegypti* is considered one of the most crucial vector whereas *Aedes niveus*, *Aedes albopictus* and *Aedes polynesiensis* have been reported as secondary vectors in most of the regions of the world [9]. *Aedes aegypti* and *Aedes albopictus* are known as the two primary vectors for transmitting the dengue in most parts of South Asia, including India. As the distribution of this affliction is concerned in respect to geographically, it is characteristically parallel to that of the principal vector species, *Aedes aegypti* [21]. Dengue mosquito is a subtropical and tropical species having distribution throughout the world [22]. Dengue virus spreads due to infected females of genus Aedes, specifically through *Aedes aegypti* in urban settings and *Aedes albopictus* in sylvatic areas [18]. *Aedes albopictus* (Diptera: *Culicidae*), is basically endemic to Pacific and Indian Oceanic islands, and from South-east Asia, it spread to America, Europe and Africa in recent decades dormant eggs in the tires. Venereal and possibly vertical transmission of dengue virus takes place by infected female of *Aedes aegypti* to its progeny (transovarian) and also from infected male to the female during the process of copulation, respectively [23].

The adult of yellow fever mosquito have approximately 4–7 mm size and it range from small to medium-sized mosquito. To the human eye, these mosquitoes are similar to the Asian tiger mosquito with a minor dissimilarity in thorax patterns and size. Adults of *Aedes aegypti* have white scales that form the shape of a violin or lyre, on the dorsal side of the thorax while the adults of *Aedes albopictus* is characterized by a white stripe to the middle at the top of the thorax region. Every tarsal portion of the hind legs exhibit white bands, this is what appear to be stripes. Abdomen is usually dark brown to black in color, but also exhibit white scales. Males are smaller than females, and can be discriminated by small palps tipped with white or silver scales. Males are characterized by plumose type of antennae; however, females possess sparse short hairs. Under a microscope, male mouthparts are viewed as modified structure for nectar feeding, and mouthparts of female are modified for feeding f blood. The proboscis from both sexes is darkly colored, and the segment above the proboscis which is known as clypeus has two clusters of white scales. A characteristic feature of all *Aedes* species is the pointed tip of

Dengue Fever: A General Perspective http://dx.doi.org/10.5772/intechopen.81277 7

*Aedes aegypti* is geographically distributed in tropical areas and it breeds in artificially filled water containers such as drums, tyres, flower vases such as plastic food containers, tin cans and old motor parts [4]. *Aedes aegypti* is a holometabolous type of insect, going through complete metamorphosis meaning four developmental stages from egg to adult stage. Life span of adult can range from 2 weeks to about 4 weeks but it depends on conditions of environment. A female mosquito lay eggs for about 4–5 times during her entire life span and average number of eggs in single spawn ranges from 10 to 100 eggs. *Aedes aegypti* are found in three different polytypic forms: sylvan, domestic, and peridomestic. The domestic type usually breeds in urban habitats, mostly inside or around houses. The sylvan type is rural form which breeds in tree holes, normally in forests, and the peridomestic form generally lives in environmentally-

As the spread of mosquitoes is concerned, it occurs by active flight (adult) and passive transportation (immature stages) through international trades. Successive waves of invasion of *Aedes aegypti* and *Culex pipiens* have been aided by commercial passages also from fifteenth century to onward. *Aedes aegypti* substituted *Aedes albopictus* in Asian countries during the

Dengue infection is transmitted by dengue virus (DV) which is a member of genus *Flavivirus*. This Arbovirus group of viruses is specifically transmitted via insect vectors. Mature viral particles have diameter of 40–50 nm, spherical shape and 11 kb, having positive single stranded RNA which has a 5′-methyl cap with a single open reading frame. Genus *Flavivirus* has 4 antigenically associated but four distinct serotypes known as DENV-1, DENV-2, DENV-3 and DENV-4 [27, 28]. The serotypes are evolved from a common ancestor and all are considered

the abdomen (**Figures 2** and **3**) [24].

**4. Life cycle of** *Aedes aegypti*

twentieth century [25, 26].

**5. The virus**

modified regions as coconut farms and groves (**Figure 4**) [24].

**Figure 2.** Difference between *Aedes aegypti* and *Aedes albopictus* (Source: http://www.mdsaude.com/wp-content/uploads/ 2012/04/aedes-aegypti-e-aedes-albopictus.jpg).

**Figure 3.** *Aedes aegypti* with its taxonomic characteristics. (a) *Aedes aegypti*; (b) Lyrix at thorax; (c) Clypeus; (d) Proboscis; (e) silvery scales on wing; (f) white stripes on leg.

The adult of yellow fever mosquito have approximately 4–7 mm size and it range from small to medium-sized mosquito. To the human eye, these mosquitoes are similar to the Asian tiger mosquito with a minor dissimilarity in thorax patterns and size. Adults of *Aedes aegypti* have white scales that form the shape of a violin or lyre, on the dorsal side of the thorax while the adults of *Aedes albopictus* is characterized by a white stripe to the middle at the top of the thorax region. Every tarsal portion of the hind legs exhibit white bands, this is what appear to be stripes. Abdomen is usually dark brown to black in color, but also exhibit white scales. Males are smaller than females, and can be discriminated by small palps tipped with white or silver scales. Males are characterized by plumose type of antennae; however, females possess sparse short hairs. Under a microscope, male mouthparts are viewed as modified structure for nectar feeding, and mouthparts of female are modified for feeding f blood. The proboscis from both sexes is darkly colored, and the segment above the proboscis which is known as clypeus has two clusters of white scales. A characteristic feature of all *Aedes* species is the pointed tip of the abdomen (**Figures 2** and **3**) [24].
