What Role Does Climate Change Have on Vector-Borne Diseases?

Although questions remain about the precise role that climate has—and, in particular, climate change—in the emergence of vector-borne diseases such as Dengue fever, Chikungunya, and Zika virus, new research has identified a significant link between El Niño-Southern Oscillation conditions in the Pacific Ocean and Dengue epidemics in Sri Lanka.

Unsurprisingly, the authors of a study published on November 4th in the International Journal of Environmental Research and Public Health, noted that El Niño activity—as measured by changes in sea surface temperature in the Pacific—has pronounced effects on rainfall and temperatures in Southeast Asian nations such as Sri Lanka, doubling, tripling, and even quadrupling precipitation totals in some areas. What is at least somewhat surprising, however, is that the researchers were also able to confirm corresponding increases in the relative risk for Dengue in the affected areas following periods in which El Niño activity occurs.

“Dengue is the major public health burden in Sri Lanka and the Kalutara district is one of the most affected areas,” study co-author Joacim Rocklöv, PhD, Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, Sweden said in a press statement released in conjunction with the article’s publication. “So understanding how reoccurring weather patterns drive Dengue is vital in controlling and preventing the disease spread.”

For their research, Dr. Rocklöv and colleagues used the Oceanic Niño Index, local weather data, and epidemiological information to assess data associations between climate and Dengue incidence and prevalence in 10 healthcare divisions of Kalutara in southwestern Sri Lanka. They analyzed weekly weather variables and data on Dengue notifications between 2009 and 2013, and developed estimates for relative risk for Dengue during periods with different climate conditions. The researchers found that relative risk for Dengue increased overall following periods of increasing weekly rainfall above the 50 mm level. At a lag of 6 to 10 weeks following rainfalls of more than 300 mm per week, relative risk for Dengue in the affected regions was observed to be as high as 1.4. Relative risk also increased as weekly rainfall totals passed the 400 mm and 500 mm levels.

Similarly, starting from a lag of 4 weeks, the overall relative risk of Dengue increased steadily as temperatures rose to 30 degrees Celsius or higher.

“Our findings showed that both rainfall and temperature were significantly associated with relative risk of Dengue in the [Kalutara] district,” they wrote. “Increasing weekly cumulative rainfall was associated with increased dengue risk starting after 6 weeks of lag. The most significant positive association was seen at lag weeks 8—10 for cumulative rainfall above 300 mm per week. Compared with a reference value of 29.8 °C, increasing weekly mean temperature over its full range was associated with an elevated risk of dengue starting after 4 weeks of lag. The study also illustrates the presence of considerable heterogeneity in temperature and rainfall effect on dengue among 10 MOH divisions.”

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.