Rise in dengue if El Nino unfolds

by Mark Leberfinger

Higher temperatures in Asia, including those during a strong El Niño cycle, can drive up the incidence of dengue fever, a group of international researchers has found.

For the first time, researchers have been able to review the big picture of dengue epidemics on a continental scale, said Dr. Wilbert van Panhuis, Assistant Professor of Epidemiology at the University Of Pittsburgh Graduate School Of Public Health.

Researchers studied 3.5 million reported dengue cases over an 18-year period from eight Southeast Asian countries. The research was published in the 5 October 2015 in an early edition of the Proceedings of the National Academy of Sciences. Dengue is transmitted through the bite of an infected Aedes mosquito. A person can contract dengue fever or a more severe form, dengue hemorrhagic fever, according to the US Centers for Disease Control and Prevention. More than 100 million dengue cases are estimated each year in the world.

“The knowledge on the strong epidemiological connections between dengue epidemics in different countries and the strong dependency on high temperatures can help to improve epidemic prediction models,” van Panhuis said. “Currently, models to predict large dengue epidemics have failed and major outbreaks continue to hit countries unexpectedly.”

The study found a strong correlation of region-wide dengue outbreaks and abnormally high temperatures, van Panhuis said.

“El Niño is one cause of these high temperatures, but not the only one. For example, high temperatures occurred in 2010, followed by a large dengue outbreak, but this was not an El Niño season,” he said.

El Niño patterns tend to favour above-normal temperatures across Southeast Asia, according to AccuWeather Chief International Meteorologist, Jason Nicholls. Much of Asia can expect seasonable to above-average temperatures this winter as the strongest El Niño in 50 years unfolds, Nicholls said.

This may correlate with an increase in dengue fever cases.

“However, cooler-than-normal waters in the western Pacific during a typical east-based El Niño can tend to hold temperatures close to normal in Papua New Guinea and eastern Indonesia,” Nicholls said. One previous study showed a relation between dengue and El Niño, but for only one province in Vietnam, van Panhuis said.

“This study was done in exactly the same time period as ours and this province was one of the 273 that we studied,” he said. “Similar to ours, this previous study found a transient correlation with El Niño –the correlation occurred only during the peak of the epidemic and not afterward.”

“This could point to a threshold effect where high temperatures [and thus El Niño] are only causing major dengue outbreaks if they exceed a certain threshold level. This warrants further study,” he added.

Van Panhuis said there is now an opportunity to substantially improve prediction models, but only if country data are polled into one dengue monitoring framework.

“If prediction models indicate a high risk of a large dengue outbreak, governments can start early with awareness campaigns to motivate the population to clean up around their houses and prevent the vector from spreading the virus,” he said.

- Accuweather