Dengue Fever in the Modern World
Wilder-Smith, A. and Gubler, D.J. 2008. Geographic expansion of Dengue: The impact of international travel. Medical Clinics of North America 92: 1377-1390.
In an effort to find a better explanation for dengue's recent global expansion, i.e., one based on real-world data, Wilder-Smith and Gubler review what is known about the problem and piece together what appears to be a logical conclusion.
With respect to the occurrence of dengue infections, the two researchers report that "climate has rarely been the principal determinant of [their] prevalence or range," and that "human activities and their impact on local ecology have generally been much more significant." In this regard, they cite as contributing factors "urbanization, deforestation, new dams and irrigation systems, poor housing, sewage and waste management systems, and lack of reliable water systems that make it necessary to collect and store water," further noting that "disruption of vector control programs, be it for reasons of political and social unrest or scientific reservations about the safety of DDT, has contributed to the resurgence of dengue around the world." In addition, they write that "large populations in which viruses circulate may also allow more co-infection of mosquitoes and humans with more than one serotype of virus," which would appear to be born out by the fact that "the number of dengue lineages has been increasing roughly in parallel with the size of the human population over the last two centuries." Most important of all, perhaps, is "the impact of international travel," of which Wilder-Smith and Gubler write that "humans, whether troops, migrant workers, tourists, business travelers, refugees, or others, carry the virus into new geographic areas," which movements, in their words, "can lead to epidemic waves."
Given these findings, Wilder-Smith and Gubler conclude that "population dynamics and viral evolution offer the most parsimonious explanation for the observed epidemic cycles of the disease, far more than climatic factors."