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Dengue Fever: How Will It Respond to Global Warming?
Reiter, P., Lathrop, S., Bunning, M., Biggerstaff, B., Singer, D., Tiwari, T., Baber, L., Amador, M., Thirion, J., Hayes, J., Seca, C., Mendez, J., Ramirez, B., Robinson, J., Rawlings, J., Vorndam, V., Waterman, S., Gubier, D., Clark, G. and Hayes, E.  2003.  Texas lifestyle limits transmission of Dengue virus.  Emerging Infectious Diseases 9: 86-89.

The twenty authors of this enlightening paper note that "it has frequently been stated that dengue, malaria, and other mosquito-borne diseases will become common in the United States as a result of global warming (Watson et al., 1996; Jetten and Focks, 1997; Patz et al., 1998; Watson et al., 1998)."  Such predictions generally are based on the concept of vectorial capacity, which has proven useful in some contexts but does not incorporate human socioeconomic factors, which appear to override almost all other considerations in the cases of these particular maladies.

What was done
In the summer of 1999, toward the end of a significant dengue outbreak in "los dos Laredos" - Laredo, Texas, USA (population 200,000), and Nuevo Laredo, Tamaulipas, Mexico (population 290,000) - the team of scientists headed by Reiter conducted a seroepidemiologic survey to examine factors affecting dengue transmission in both of these cities, which lie adjacent to each other on opposite sides of the Rio Grande, but which experience, according to the authors, "massive cross-border traffic across three multi-lane bridges."

What was learned
It was determined that "the incidence of recent cases, indicated by immunoglobulin M antibody serosurvey, was higher in Nuevo Laredo [16.0% vs. 1.3%], although the vector, Aedes aegypti, was more abundant in Laredo [91% vs. 37%]."  Reiter et al. additionally determined that "environmental factors that affect contact with mosquitoes, such as air-conditioning and human behavior, appear to account for this paradox."  They found, for example, that "the proportion of dengue infections attributable to lack of air-conditioning in Nuevo Laredo [where only 2% of the homes had central air-conditioning compared to 36% of the homes in Laredo] was 55%," which means that 55% of the cases of dengue in Nuevo Laredo would not have occurred if all households there had had air-conditioning.

What it means
Climate-alarmist scare stories about mosquito-borne diseases running rampant in a CO2-enriched warmer world are just that: stories concocted to scare people into doing what they clearly would not do (drastically reduce their use of fossil fuels) if told the truth of the matter.  Reiter et al. correctly conclude, for example, that "if the current warming trend in world climates continues, air-conditioning may become even more prevalent in the United States, in which case, the probability of dengue transmission [there] is likely to decrease [our italics]."  And if the economy of Mexico continues to grow (which it will, if its citizens are allowed to freely utilize fossil fuels), the use of air-conditioners will likely gain momentum south of the border, which would lead to even greater decreases in the occurrence of dengue there.

Clearly, the development of wealth, which currently is dependent on the availability of fossil-fuel-derived energy, will lead to greater decreases in mosquito-borne diseases than any change or stasis of climate ever would.

Jetten, T.H. and Focks, D.A.  1997.  Potential changes in the distribution of dengue transmission under climate warming.  American Journal of Tropical Medicine and Hygiene 57: 285-297.

Patz, J.A., Martens, W.J.M., Focks, D.A. and Jetten, T.H.  1998.  Dengue fever epidemic potential as projected by general circulation models of global climate change.  Environmental Health Perspectives 106: 147-153.

Watson, R.T., Zinyowera, M.C. and Moss, R.H.  (Eds.)  1996.  Impacts, Adaptations and Mitigation of Climate Change: Scientific-Technical Analyses.  Contribution of Working Group II to the Second Assessment of the Intergovernmental Panel on Climate Change (IPCC).  Cambridge University Press, Cambridge, UK.

Watson, R.T., Zinyowera, M.C. and Moss, R.H.  (Eds.)  1998.  The Regional Impacts of Climate Change: An Assessment of Vulnerability.  Special Report of the Intergovernmental Panel on Climate Change (IPCC) Working Group II.  Cambridge University Press, Cambridge, UK.

Reviewed 24 March 2004