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Context: A new study published in the journal Science has identified a possible connection between sea-surface temperature anomalies in the Indian Ocean and the severity of dengue epidemics worldwide.

Study Objective

• The study aimed to investigate the relationship between anomalies in sea-surface temperatures in the Indian Ocean and the intensity of dengue epidemics worldwide. Specifically, the researchers explored whether variations in the Indian Ocean basin-wide (IOBW) index could predict the magnitude and timing of dengue outbreaks in different regions.

Dengue fever is a mosquito-borne viral infection caused by the dengue virus, transmitted by Aedes mosquitoes. The disease is a significant public health concern globally, with approximately 100-400 million infections occurring each year and a prevalence in almost half of the world's population.

Methodology

• Data Collection: The researchers collected data on annual dengue cases reported from 46 countries in Southeast Asia and America over 30 years (1990-2019). Monthly dengue case reports from 24 countries over six years (2014-2019) were also analysed to assess seasonal variations.
• Climate Patterns Analysis: The team analysed global climate patterns, focusing on the Indian Ocean basin-wide index (IOBW). This index represents average sea-surface temperature variations across the tropical Indian Ocean.
  • Teleconnections, which are large-scale atmospheric patterns transferring heat and moisture across vast distances, were examined for their influence on regional temperatures and dengue transmission.

The Indian Ocean Basin-Wide (IOBW) Index is a measure of the average sea surface temperature (SST) across the tropical Indian Ocean. It's become a significant tool for predicting the likelihood and scale of dengue outbreaks in various countries.

Key Findings

• The study found a close association between the IOBW index and dengue outbreaks in both the Northern and Southern hemispheres. Variations in the IOBW index significantly influenced local temperatures worldwide, affecting dengue transmission dynamics.
• The IOBW index emerged as a key indicator for predicting the magnitude and timing of dengue epidemics in different countries. Dengue incidence exhibited seasonal peaks, with the Northern Hemisphere experiencing outbreaks between July and October, and the Southern Hemisphere between February and April.
• The amplitude of dengue outbreaks was higher when the IOBW index was positive (indicating warmer sea-surface temperatures) and lower when it was negative.

Significance of the Study

• Understanding the relationship between Indian Ocean temperatures and dengue outbreaks could facilitate the development of early warning systems. Predictive models based on the IOBW index may provide sufficient lead time for public health authorities to prepare and implement targeted interventions.
• The study highlighted differences in the IOBW index's impact on dengue incidence between the Northern and Southern hemispheres. Countries in the Southern Hemisphere, such as Brazil, exhibited a stronger association between the IOBW index and dengue transmission.

Limitations of the Study

• The study emphasises the need for more data to establish causality, confirming that variations in the IOBW index directly influence local temperature changes and subsequent dengue incidence.
• Other factors influencing dengue transmission, such as vector control measures, socio-economic factors, and local immunity levels, were not fully evaluated in this study.
• Future research should incorporate these factors into comprehensive early warning systems for dengue outbreaks.

Conclusion

• The study highlights the potential of using the Indian Ocean basin-wide index as a valuable indicator for predicting the magnitude and timing of dengue epidemics globally. This research contributes to enhancing public health preparedness and response strategies, ultimately aiding in the control and mitigation of dengue outbreaks on a global scale.

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Down to Earth

PRACTICE QUESTION Q. What does the Indian Ocean basin-wide (IOBW) Index represent? A) Average wind speed in the Indian Ocean B) Variations in sea-surface temperatures across the tropical Indian Ocean C) Depth of the Indian Ocean D) Salinity levels in the Indian Ocean Answer: B