Spatio-Temporal Patterns of Dengue Fever in Cali, Colombia

Introduction

Dengue fever is an arboviral disease of considerable importance due to its endemic nature. In recent decades it has grown dramatically, reaching a global presence in more than one hundred countries (Kittayapong et al., 2008), while it remains a threat to more than 2.5 billion people, particularly in tropical and subtropical areas, in rural as well as urban settings. Between fifty to one hundred million people are infected every year, creating a burden to communities and health entities that need to control and prevent the virus from becoming an epidemic (Méndez et al., 2006; WHO, 2009).

The disease is transmitted to humans by mosquitoes of the genus Aedes (Monath, 1988). The mosquito, Aedes aegypti, inhabits and reproduces in warm temperature areas generally between 18° and 25° C (Wu et al., 2009). There is a temperature threshold below which the mosquito cannot survive and as temperature increases it is required to feed, which may eventually lead to an increasing rate of biting events. Higher temperatures, therefore, shorten the probability of mosquito survival (Kolivras, 2006). The Aedes aegypti mosquito tends to be more active during daytime, especially in the close proximity of houses (Halstead, 1997). The mosquito’s habitat is, most often, artificial water holding containers where they develop and lays eggs. This fact ties them to households, given that it is here where these containers are kept to store water for drinking and other household shores (a practice often observed in the developing world countries both in rural and urban areas). This means that transmission is generally focal, clustering in households and nearby neighbors over short periods of time (Kuno, 1995; Getis et al., 2003; Morrison et al., 1998). Only adult females transmit the virus to humans. The incubation period of the virus is around ten days, after which the virus replicates in the salivary glands of the Aedes aegypti mosquito. Symptoms of the disease include fever, joint and back pain (which has given the disease the name “break bone fever” (Suarez et al., 2005), severe headache, and nausea (Kolivras, 2006).

Dengue fever studies have focused in understanding patterns between mosquito infected areas and infected individuals (Chang et al., 2009); identifying causal relationships, in particular weather and vegetation (Tipayamongkholgul et al., 2009; Kolivras, 2006; Arboleda, Jaramillo-O and Peterson, 2009; Braga et al., 2010; Johansson, Dominici & Glass, 2009; Maciel-de-Freitas et al., 2010; Maria & Valencia, 2011; Wu et al. 2009); and spatio-temporal patterns of infected individuals (Eisen & Lozano-Fuentes, 2009; Getis et al., 2003; Mammen et al., 2008; Morrison et al., 1998; Rosa-Freitas et al., 2003; Tran et al., 2004; Kan et al., 2008). The disease is known to vary through time and space, due to a number of factors including the human host, the virus, the mosquito vector and the environment (Mammen et al., 2008). Determinant factors in the transmission include: mosquito density, circulating virus serotypes, and susceptibility of human populations (Kuno, 1997).