New research shows that epidemics of dengue—caused by a mosquito-borne virus—across southeast Asia appear to be linked to the abnormally high temperatures brought by the El Niño weather phenomenon.
Now, as the most intense El Niño in nearly two decades is emerging in the Pacific, the finding, reported the Proceedings of the National Academy of Sciences, may be a harbinger of a spike in cases of the dangerous hemorrhagic fever throughout southeast Asian countries early next year.
“Large dengue epidemics occur unexpectedly, which can overburden the health care systems,” says lead author Willem G. van Panhuis, assistant professor of epidemiology at the University of Pittsburgh Public Health.
“Our analysis shows that elevated temperatures can create the ideal circumstance for large-scale dengue epidemics to spread across a wide region. The ability to predict and prepare for these epidemics should lead to more effective disease surveillance and control efforts.”
390 million infections each year
Dengue causes an estimated 390 million infections each year. Though there is no specific pharmaceutical treatment, supportive therapy can greatly improve outcomes.
“Dengue infects large numbers of people across the tropics each year, but incidence can vary dramatically from year to year in any setting,” says lead author Derek Cumming, a biology professor at the University of Florida and member of the Emerging Pathogens Institute.
“During years of large incidence, the number of people requiring hospitalization and care can overwhelm health systems. If we can understand the factors that contribute to these increases, we can prepare for them and act to mitigate the impact of the disease.”
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The research team collected and analyzed 18 years of monthly dengue surveillance reports on a total of 3.5 million reported cases in 273 provinces in eight countries in southeast Asia. By bringing the data together from several countries, the scientists were able to see patterns—or synchronicity—in dengue transmission across the entire region.
“This is another example of extracting valuable information from routinely collected public health data that was just sitting around in basements and computer archives across these countries,” says van Panhuis.
El Niño and hotter weather
In 1997 and 1998, dengue transmission was very high, matching up perfectly with high temperatures that allowed mosquitoes to reproduce faster and spread dengue virus more efficiently. These high temperatures were caused by an exceptionally strong El Niño season, which occurs when rising sea water temperatures in the eastern Pacific move westward. This phenomenon occurs about every five years, with one of the largest episodes expected in the coming months.
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This study also found that urban areas act as dengue epidemic “pacemakers” because of their constant supply of new people who are susceptible to dengue. In addition, traveling waves of large epidemics were found to emerge from west Thailand, central Laos, and the southern Philippines.
“Given the increased cross-border mobility of people, strong evidence of global warming, and the potential for rapid global proliferation of infectious diseases, a better understanding of how contagious diseases spread over long distances is essential for global health security,” says van Panhuis.
The Bill and Melinda Gates Foundation and the National Institutes of Health National Institute of General Medical Sciences supported the work.
