Dengue fever is one of the most important arboviral infections of man and is responsible for more illness and deaths among humans than any other arboviral disease (WHO, 1997). More than 2.5 billion people live in areas where the disease is endemic, and this includes more than 100 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. Southeast Asia and the Western Pacific are the most seriously affected areas (WHO, 1997).
The vector of the disease is different species of the Aedes mosquito—Aedes aegypti in the Caribbean. This is a tropical and subtropical species of mosquito usually found between latitudes 35°N and 35°S, an area that roughly corresponds to the winter isotherm of 10oC for January (or July in the Southern Hemisphere). Although the vector has been found as far as 45°N and 40°S, such invasions in the warm season have not survived the winters (Tabachnick and Powell, 1979). The influence of temperature on Aedes aegypti and on the transmission of dengue is manifested in several ways. Temperature affects the rate of larval development, adult survival, vector size, and efficiency (Wilson, 2001). In addition, temperature affects the extrinsic incubation period, which is the time needed for viral multiplication and invasion of the salivary glands of the mosquito. This must occur before the next infectious blood meal can take place (Wilson, 2001).
The vector is highly domiciliated and breeds in water storage containers and receptacles found within the home. It thrives in urban environments where environmental sanitation is poor; where water collects in blocked drains, improperly discarded tires, bottles, and coconut shells (WRI, 1998). Its larvae are also encountered in tree holes and herbaceous plants in which rain water collects. So rainfall is necessary for breeding in outdoor habitats. The eggs can resist desiccation for up to one year and hatch when sites are flooded with water. This explains why the mosquitoes can emerge as if from nowhere at the end of long, dry spells.
The disease is caused by any of the four serotypes of the arbovirus known as dengue-1, dengue-2, dengue-3, and dengue-4. These four serotypes are epidemiologically similar but genetically and antigenically distinct. Infection with one serotype leads to protection against homologous reinfection but provides only brief protection against heterologous infection (WHO, 1997). Sequential infection increases the risk of acquiring the more deadly dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) because of the severity of antibody response (Valdes et al., 2000). The propagation of the virus appears to be dependent on human populations with a sufficient number of susceptible members to support infection (Ehrenkranz et al., 1971).
The symptoms of the disease appear within four to six days of being bitten by an infected mosquito, and in the early stage, it may be nonspecific and may be very easily mistaken for illnesses such as influenza. There is a sudden onset of high fever, headaches, severe muscle and joint pains, and pain behind the eyes. These symptoms can last up to 10 days, but complete recovery can take up to one month. These symptoms are mild compared with those of DHF, in which the blood vessels can leak, causing bleeding of the nose and gums and can eventually collapse giving rise to the oft fatal dengue shock syndrome (DSS), which has a fatality rate of 5 percent.
