Already endemic in over 110 countries, and with almost 50 million cases annually, dengue fever continues to spread. Incidences have increased almost 30-fold in the past 50 years. Although rarely fatal, the disease costs Latin America and the Caribbean around $2.1 billion annually. Being a vector-borne disease, it is spread by mosquitos that frequently lay their eggs in standing water that is common near households in many tropical countries. Previous research has shown that dengue fever exhibits seasonal patterns, which means that climate change might affect its spread.
To investigate the linkages between climate change and dengue fever, Colon-Gonzalez et al. used a Generalized Additive Model informed by 23 years of province-level data from Mexico to better understand how the incidence rate of the disease changes with minimum and maximum temperature and rainfall. The authors then used these estimates along with a number of global climate models to predict how the incidence rate will change using 3 different climate scenarios.
The authors found interesting and highly non-linear results. There was almost no risk of dengue when minimum temperatures were below 5°C and a rapidly increasing risk above 18°C. Maximum temperature also showed non-linear trends with a peak incidence at around 32°C and declining risk above and below this temperature. Likewise, the risk of dengue peaked at around 550mm of annual precipitation with declining risk for greater and lesser amounts of rain.
The authors speculate that increased rainfall creates more opportunities for rain-filled outdoor breeding sites. However, when there is too much rain these sites are washed out. Interestingly, increasing access to piped water systems showed a strong positive correlation with dengue incidence. This is presumably because the intermittent nature of such systems forces local residents to store their water uncovered for long periods.
Results of Gonzalez, et al. indicate that temperature and precipitation changes due to climate change will increase dengue incidence across Mexico by 12-18% by 2030, 22-31% by 2050 and 33-42% by 2080. Incidence will increase most dramatically in the hot and humid southern and eastern climates where the disease is already endemic. Overall, dengue incidences are likely to increase by 70,000 to 189,000 extra cases per year. There is also a fear that climate change might increase the incidence of more severe forms of dengue through secondary infections.
Unfortunately, since dengue fever has no cure, the only option for Mexico and other endemic countries is to prevent transmission through better water storage practices and improved water supply systems.
Map Source: Slide #8 of a presentation by Gary G. Clark, PhD, entitled “Dengue: An emerging arboviral disease”. Agricultural Research Service of the US Department of Agriculture.
Colón-González, F. J., Fezzi, C., Lake, I. R., & Hunter, P. R. (2013). The Effects of Weather and Climate Change on Dengue. PLoS neglected tropical diseases, 7(11), e2503.
Special Programme for Research, et al. Dengue: guidelines for diagnosis, treatment, prevention and control. World Health Organization, 2009.
Shepard DS, Coudeville L, Halasa YA, Zambrano B, Dayan GH (2011) Economic Impact of Dengue Illness in the Americas. Am J Trop Med Hyg 84: 200–207.