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From Brazil to Bangladesh, via Burkina Faso and France, countless regions worldwide have experienced unprecedented outbreaks of the mosquito-borne disease dengue this year, afflicting entire communities and placing exceptional strain on health systems and healthcare staff. The number of officially reported dengue cases soared to over 10 million globally in 2024, a staggering rise from around half a million in 2000. The World Health Organization (WHO) ranked dengue fever as a top-10 global health threat in 2019, and just this year raised the response to the dengue threat to a Grade 3, the highest level possible. According to WHO estimates, there are likely to be around 390 million dengue cases worldwide, and close to half the world’s population is at risk of this disease.
Historical and Modern Factors in Dengue Acceleration
The current-day global expansion of dengue infections can be traced back to several leading global phenomena. These include the acceleration in globalisation, migration, and international trade from the 1970s, when dengue outbreaks were recorded in just 9 countries in contrast to the present where it is found in over 120 countries. The roots of this are well illustrated by the historical experience of the Asia region, where until recent years, around 75% of dengue cases had been found. As regional urbanisation and populations migrated towards cities, often in sub-optimal conditions including makeshift water storage which provided mosquitoes with suitable breeding sites, the dengue-transmitting mosquito (genus Aedes) established itself and flourished, introducing the dengue virus to new regions. Subsequent movements in goods and people across the globe have facilitated the spread of the disease-carrying mosquitoes to new lands.
Impact of Climate Change on Dengue
These dynamics have been compounded by climate change. Over the past 50 years, dengue incidence has increased 30-fold, while global temperatures rose almost twice as fast as in the previous half-century. Dengue, like many infectious diseases, is affected by climatic and seasonal variations, such as temperature shifts, flooding, drought, and El Niño cycles. Mosquitoes, being ectothermic or dependent on external sources of body heat, experience intensified biological processes in warmer weather. Droughts lead to water storage, boosting mosquito breeding, and severe weather events cause inadequate housing and sanitation, promoting mosquito populations. Additionally, climate-sensitive coexisting conditions like malnutrition or heat-related health issues worsen dengue outcomes.
Global Efforts and Challenges in Combating Dengue
The recent rise of dengue on the global health agenda has accelerated efforts to understand, prevent, and combat this threat across multiple sectors. Increased awareness and advocacy have educated communities and authorities about mosquito-borne diseases, increasing prevention measures from policy to grassroots levels. This has also improved healthcare professionals’ expertise in managing dengue patients, crucial for detecting and triaging those at risk of severe forms, as no specific dengue treatment exists. Therapeutically, promising dengue vaccines are available or in development, with coordinated efforts to ensure access for those in need despite complex outbreak contexts. On the curative front, stakeholders are close to delivering the world’s first dengue treatment. Innovations in vector control, such as new insecticides and Wolbachia-enhanced mosquitoes, are also helping reduce dengue transmission.
World Mosquito Day on August 20th provides a timely reminder that we stand at an important point for mosquito-borne diseases. Undeniably, dengue and its mosquito vectors have spread alarmingly across the world in the last decades. Climate change and international travel have exacerbated the spread and duration of dengue outbreaks. Simultaneously, the world has never been so close to benefiting from concrete preventive and curative solutions, as well as a renewed sense of urgency on the need for international cooperation on global health threats.
A number of challenges however should dictate where the next wave of efforts could impact the most. Firstly, the evidence of four distinct types of dengue, the geography of which over time and at present remains insufficiently studied, continues to pose significant challenges from surveillance to immunology; this requires better understanding. This is closely linked to shortcomings in the diagnosis and active surveillance of dengue resulting in difficulties in evaluating the true burden of dengue, its evolution over time, and most importantly the potential oversight of concurrent and equally devastating outbreaks of diseases such as chikungunya and Zika.
Urgent Call for Investment and Cooperation in Healthcare Systems
Investment in this sector and support to healthcare systems are crucial, as are improved mechanisms for data reporting and sharing across nations. Global challenges such as displaced populations, conflict, and unplanned massive urbanisation will provide ideal contexts for disease-harbouring mosquitoes to further cause overwhelming outbreaks whilst simultaneously hindering the required healthcare interventions. International and cross-sector cooperation is more urgent than ever, and there is much to learn from regions like Southeast Asia, with long-standing experience of successful partnerships and interventions, as well as challenges.
