Dengue is a mosquito-borne disease that has recently spread across tropical and subtropical regions to now affect over half the world’s population. The annual number of reported dengue cases has been increasing over the past 20 years and 2023/2024 has seen the worst outbreak ever with over 6.6 million cases reported in the past 12 months.

There are no specific treatments for dengue, and therefore authorities focus on preventing infections using interventions such as insecticides that kill mosquitoes. These interventions are much more effective if they can be used before an outbreak develops rather than in response to rising cases when it might already be too late.

To anticipate these outbreaks authorities are increasingly turning to computational forecasting models that use the intrinsic delayed links between climate (particularly temperature and rainfall), mosquito growth rates and dengue risk. Such models are increasingly capable of forecasting dengue outbreaks up to 1-2 months ahead, but often longer-term projections are needed to be prepared for larger outbreaks.

This study, published today in Science, identifies a new link between a macroclimatic indicator and long-term dengue trends. Temperatures in the Indian Ocean were found to trigger a cascade of climatological events that make areas worldwide more suitable for dengue. Monitoring temperatures in the Indian Ocean in real time using satellites could have the potential to increase the horizon of dengue forecasts out to 6 months or more, increasing the change than dengue outbreaks can be prevented.

Oli Brady, joint senior author on the study and Associate Professor at LSHTM commented on the opportunities that are now available to dengue forecasters:

“Understanding the link between complex climate phenomena and dengue offers new opportunities to forecast and prevent outbreaks but also tells us how risk might vary with climate change. Discoveries like this have only recently been made possible because of pooling of large publicly available datasets on dengue from around the world.”

This research highlights the potential for using broader climate indexes such as the IOBW to support the WHO's Neglected Tropical Diseases Roadmap in establishing indicators for monitoring and managing diseases like dengue.