Warmth promotes dengue spread; effects of rainfall on its outbreak can vary: Study

New Delhi: While rising temperatures consistently promote the spread of dengue, rainfall could either increase or decrease the spread, depending on how long a region has experienced a dry season, a study has found.

As warmer, humid conditions, driven by climate change, increase dengue outbreaks, including in countries previously unaffected, the study, published in the journal Science, detailed how temperature and rainfall interact, and affect disease spread.

Researchers, led by those from Korea Advanced Institute of Science and Technology and the Institute for Basic Science, stressed on the role of local climate conditions in spreading dengue, thereby warranting tailored strategies in preventing disease.

Dengue is a viral infection, caused by the bite of an infected mosquito. Climates of tropical and sub-tropical regions are known to favour the disease's spread, mostly in urban and semi-urban areas.

Focussing on 16 regions of the Philippines, known for their diverse climate, the researchers analysed five years' data, recorded between January 2015 and December 2019.

While rising temperatures were consistently related with a higher rate of dengue spread across the regions, rainfall was found to increase disease spread in eastern regions and decrease it in western ones.

The team explained that the contrasting effects of how rainfall affected the spread of dengue depended on a "previously overlooked" critical factor -- 'variation in dry season length', which refers to the differences in how long a dry season (with little to no rainfall) lasts between varied geographic regions.

In regions seeing fewer changes in the duration of dry season, rainfall tended to flush out stagnant water, reducing breeding sites for mosquitoes, thereby suppressing dengue spread, the researchers said.

However, in regions experiencing more changes in dry season length, sporadic rainfall created new breeding sites and weakened the flushing effect, thereby driving an increase in mosquito populations and dengue cases.

"Our findings provide robust evidence for how climatic factors influence dengue transmission in diverse environments. This represents a significant step toward understanding how climate change may impact mosquito-borne diseases globally," first author Olive R. Cawiding, from Korea Advanced Institute of Science and Technology and the Institute for Basic Science, said.

To validate their findings, the researchers extended their analysis to Puerto Rico, another region with diverse climate patterns. Data from municipalities, including San Juan, Adjuntas, and Ponce, covering a 20-year period from 1986 to 2005 was analysed.

The findings revealed similar patterns in how rainfall regulated the spread of dengue and "aligned with the results from the Philippine data".

"We found that temperature consistently increased dengue incidence throughout all the regions, while rainfall effects differed depending on the variation in dry season length, a factor previously overlooked," the authors wrote.

"Our findings emphasise the need for tailored prevention strategies based on local climate conditions, rather than a one-size-fits-all approach," they wrote.