Dengue is arguably the most important arboviral disease (i.e. virus spread by arthropod vectors, see below) in the world, potentially impacting 2.5-3 billion people (see links). Dengue is not well known in temperate climes, such as in the US, for its tropical preferences. Dengue does potentially affect folks in the US, especially in the South, and certainly had its toll on soldiers in Southeast Asia.
Dengue is vector-borne, like its more famous cousin (in tropical-disease terms), malaria. That is, the spread of dengue amongst a population of humans is caused by a vector or agent of its transmission. In this instance, the culprit is the
Aedes aegypti mosquito (where
Anopheles spp. mosquitos are culpable for malaria transmission), who also is the vector of urban yellow fever.
While dengue is not as deadly as malaria, the sheer scale of its impact each year and the economic losses due to caring for people afflicted by it make it as important as other high-profile diseases, such as HIV. Moreover, dengue is complicated because there are 4 distinct viral serotypes, none of which induce cross-immunity (i.e. you could get sick with all 4), and serial infection potentially leads to dengue haemorrhagic fever and dengue shock syndrome, both terrible and primarily pediatric conditions with mortality rates that can approach 15% (usually ~ 5%). The plurality of dengue strains makes complicated the development of an effective vaccine, and to date there is none, though efforts are underway. Hence, the only effective means of controlling dengue currently (and especially in the many poor parts of the world where it is found), is to focus on the factors underlying its spread. Namely, the interactions between humans and mosquitos.
Mosquito control programs at one time were effective in abating dengue risk. Massive efforts to eliminate or reduce 'sources'--i.e. water holding containers suitable for mosquitos to lay eggs in--and pesticide spraying--especially DDT--reduced
Ae. aegypti population densities dramatically throughout tropical latin and South America. Success was fleeting, however, as efforts flagged for numerous reasons.
Ae. aegypti has since made a significant comeback with a current distribution that is perhaps greater than it ever was and may be even more significant in a climate that is rapidly warming (though an effect of climate change on dengue,
per se, has yet to be documented). It isn't, perhaps, incorrect to say that we are in the midst of a global dengue pandemic given its reemergence on the wings of a spreading population of Ae. aegypti and the increasing urbanization of human populations. In the absence of a vaccine, things are likely to get much worse before they get better.
Effectively controlling dengue within communities relies on the capacity to predict outbreaks and stop them before they can get rolling. Keeping tabs of
Ae. aegypti populations is an important means of acheiving such awareness. Basically, simple principles predict that as the number of mosquitos increases, so should the risk of dengue transmission, because the probability of susceptible individuals getting bit by dengue infected mosquitos should increase. Various indices exist that attempt to measure mosquito density (indices proxy for actual population densities, because these are much more difficult to estimate directly and in public health, efficiency is crucial) do not, however, do a good job of anticipating dengue incidence (people getting sick). The question is, why? Understanding this potentially helps us better anticipate dengue outbreaks. And it is the subject of my current research as part of a team led by Dr. Thomas Scott at UC Davis.
Centers for Disease Control fact sheet on denguePediatric Dengue Vaccine Initiative
