Imma Perfetto
Cosmos science journalist
Researchers have identified a global climate indicator which they say might help improve predictions of dengue outbreaks months in advance.
A study, published in the journal Science, found the Indian Ocean basin-wide (IOBW) index, which measures temperature fluctuations at the surface of the Indian Ocean, closely correlated to annual dengue incidence in the northern and southern hemispheres.
Having reliable long-term predictions could help tackle the disease by planning control measures against the mosquitoes that transmit the disease and enabling countries to mobilise hospital staff and equipment.
“The dynamics of dengue are complex because the virus exists in four different forms, or serotypes, which can change from one year to the next and one country to the next,” says Simon Cauchemez, joint last author of the study and Head of the Mathematical Modelling of Infectious Diseases Unit at the Pasteur Institute, France.
“The magnitude of dengue outbreaks can vary considerably from one season to the next.”
Most cases are asymptomatic but those with mild dengue disease may experience symptoms such as high fever, headache, body aches, nausea, and rash.
But while infection with 1 dengue serotype provides lifelong protection against that serotype, it does not provide protection for other serotypes. Instead, severe dengue disease most commonly occurs after a subsequent dengue infection with a different serotype of the virus and may result in death.
According to the World Health Organization, incidence of dengue has grown dramatically around the world in recent decades.
“The highest number of dengue cases was recorded in 2023, affecting over 80 countries in all regions. Since the beginning of 2023 ongoing transmission, combined with an unexpected spike in dengue cases, resulted in a historic high of over 6.5 million cases and more than 7,300 dengue-related deaths.”
Reproduction and infectivity of Aedes genus mosquitoes that transmit dengue viruses are closely correlated with local temperature and rainfall. However, weather parameters can only be predicted between 2 weeks and 3 months in advance. Global climate indicators, on the other hand, can generally be predicted beyond 6 months.
The international team compiled a large dataset of worldwide dengue incidence from 1990 to 2019 to see which of 30 global climate indicators predict the magnitude and timing of local and remote outbreaks.
“Our results revealed that incorporating the IOBW index into our mathematical model resulted in predictions that closely matched real-world data, compared to the model excluding the IOBW index,” says Huaiyu Tian, co-last author of the study and Director of the Center for Global Change and Public Health at Beijing Normal University, China.
“The extended lead time and improved predictive ability underscore the significance of the IOBW index in dengue forecasting and early warning systems.”
Cauchemez says their aim is to develop predictive models for dengue outbreaks in Guadeloupe, French Guiana and Martinique, and explore whether the IOBW index can effectively improve these predictions.
“Climate is not the only factor that influences dengue outbreaks,” says Cauchemez.
“For these predictive models we will also need to take into account other factors like immunity levels in the population, strains previously in circulation, etc.”
