Can changes in Indian Ocean temperatures help predict dengue outbreaks? New paper finds links

Researchers have found a potential link between anomalies in sea-surface temperatures in Indian Ocean and the intensity of dengue epidemics globally, offering hope for improved prediction of dengue outbreaks. The predictions could give countries enough time to prepare and respond.

A new paper published in journal Science identified a specific indicator, the Indian Ocean basin-wide (IOBW) index, which represents the average sea-surface temperature variations across the tropical Indian Ocean. This index, according to the study, exhibits a close association with dengue outbreaks in both the Northern and Southern hemispheres. 

Read more: Dengue: Heavy rains during July 2023 led to outbreaks across India

The link between the Indian Ocean’s temperature and dengue incidence is likely due to its influence on regional temperatures through teleconnections, large-scale atmospheric patterns that can transfer heat and moisture across vast distances.

“Our study demonstrates that the IOBW index substantially affects the local temperature worldwide, influencing dengue transmission,” the researchers wrote in their paper.

Dengue is a viral infection transmitted through the bite of infected Aedes species mosquitoes. Before 1970, severe dengue outbreaks were only reported in nine countries but now it affects nearly half of the world’s population, with an estimated 100–400 million infections occurring each year.

Early warning systems could help public health authorities anticipate and prepare for dengue outbreaks.  Temperature and rainfall have previously been linked to epidemics, but they provide a lead time of only around two weeks to three months, the researchers noted.

So the team gathered the total number of annual dengue cases reported from 46 countries in Southeast Asia and America over 30 years from 1990 to 2019.

They also looked at the dengue cases reported every month from 24 countries over six years from 2014 to 2019. Next, they analysed how global climate patterns influenced the seasonal and interannual magnitude of dengue epidemics.

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The IOBW emerged as a key indicator for predicting the magnitude and timing of dengue epidemics in each country. 

The Northern Hemisphere witnesses a peak dengue epidemic period between July and October and the Southern Hemisphere in February and April, both in the summers.

Further, the amplitude of dengue incidence was high when the index was positive and low when it was negative.  

Also, the annual dengue incidence is correlated with the IOBW index in both the Northern and Southern hemispheres.

These initial findings suggested that the index could be a potential indicator to forecast the interannual and seasonal magnitude of global dengue epidemics.

The researchers, however, add that IOBW index’s association with the Southern Hemisphere is stronger than that with the Northern Hemisphere.  The index has a more pronounced impact on temperatures in tropical regions. Brazil, for example, bears a higher burden of dengue in the Southern Hemisphere. 

Read more: Is it climate change that impacts trajectory of dengue in India?

Though promising, the researchers stress that more data is needed to establish causality, meaning that IOBW influences local temperature changes and the resultant increase in dengue incidence in other countries. 

They also acknowledge a few limitations of the study. For example, the team could not fully evaluate the IOBW index as some countries did not have publicly available annual and monthly case reports.

The study does not consider other factors that may influence dengue transmission, such as vector control measures, social and economic factors, and local herd immunity. 

“Future research should focus on incorporating other potential factors and establishing a comprehensive set of indicators for a dengue early warning system,” the researchers wrote in their study.

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