Dengue fever has also been associated with population increases, and poor vector control. In the past 50 yr, occurrences have become more prolifi c particularly in tropical cities of developing countries (CDC 2011; WHO 2009b). On average, one or more dengue viruses infect more than 2.5 billion people a year (Halstead 2007). Like malaria, the virus is also sensitive to changes in climate. One study found that a 3-4ºC increase in temperature could more than double the reproduction rate of the fourviruses (Koopman et al. 1991 as quoted in IPCC, 1998; Van Kleef et al. 2011). The disease is principally transmitted by the Aedes aegypti mosquito, which is frequently referred to as a “domesticated mosquito”. Patz et al (2005) explain that this mosquito is strongly infl uenced by both climate and human drivers. Temperature, rainfall and humidity, as well as climate change, impact A. aegypti in a similar vein to the malaria vector, through changes in reproduction rates and feeding behavior (IPCC 1998; Van Kleef et al. 2011). However, unlike Anopheles, A. aegypti predominantly breeds in urban and peri-urban areas, around human dwellings with inadequate water and waste management systems (Shope 1992). Common breeding sites are fl ower pots, water jars, and non-degradable containers that accumulate water. The virus has also been detected in rural areas in Africa, where the mosquito breeds in tree holes and concave leaves as well as around households (WHO 2009a). The breeding habitat of A. aegypti allows the species to fl ourish in high and low rainfall areas. While, peak transmission is generally after the rainy season when water sources abound, the mosquito is also successful in drought-like conditions as households are more likely to store more water. Increasing population movement from rural to urban areas has escalated the number of cases of dengue (WHO 2009a). Unplanned urbanization results in overcrowded areas that lack basic services, such as access to potable water and sanitation. In SubSaharan Africa (SSA), almost 72 percent of the urban population lives in slums (UN-Habitat 2006). Transmission effi ciency will continue to improve as warmer temperatures facilitate mosquito population growth and urbanization compacts people in sub-standard living environments fi lled with potential breeding sites. Higher chances of infection will increase the likelihood of Dengue Haemorrhagic Fever. Individuals already infected with one dengue serotype are more likely to suffer severe consequences when infected with another (Shope 1992). While demographic changes are undoubtedly increasing outbreaks, models show that climate change may be responsible for placing an additional one billion people at risk. Hales et al. (2002) modeled the population at risk and forecasted the impacts of population growth with and without climate change. The results showed that 3.2 billion will be at risk in 2055 due solely to population growth
and 4.1 billion when climate change is considered. Modeling predicted increases as well as geographic expansions and contractions.