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More heat, flooding and other climate extremes increase global threats from mosquito-borne diseases
Katie Anders is an epidemiologist and director of impact assessment at the World Mosquito Programme. Alex Jackson is WMP news editor.
As devastating floods affect more than 33 million people in Pakistan, another major threat is imminent. Public health experts warn of an increased risk of mosquito-borne diseases, for example, spreading across the country.
Pakistan is already grappling with rising cases of dengue, and this year’s unusually early and heavy monsoon rains have created favorable conditions for mosquito breeding.
In most parts of the world, the severity and regularity of extreme weather events, including droughts, heat waves, floods and heavy rains, are increasing. And an alarming new study has concluded that among the many infectious diseases that could be worsened by climate change, diseases such as mosquitoes will be most affected.
Dengue, also known as “broken bone fever” because of the intense pain it can cause, is the fastest-growing tropical disease in the world. The viral infection is transmitted to humans by the bite of female Aedes mosquitoes that thrive in tropical and subtropical urban areas.
Currently, more than half of the world’s population is at risk of contracting dengue, with 390 million people infected each year. A record 5.2 million cases of dengue were reported worldwide in 2019, and economists estimate the global cost of dengue to be close to $9 billion annually.
In Asia, countries including Malaysia, Vietnam, Singapore and the Philippines are in the midst of major dengue outbreaks. Experts in Brazil worry that the recent increase in dengue transmission is affecting many parts of the country where dengue did not occur before, and 8.7 million Brazilians are at risk of new cases of dengue compared to five years ago.
Transmission of mosquito-borne diseases such as dengue is an inherently climate-sensitive process. A temperature increase of just a few degrees can accelerate mosquito development, prolong survival, and even increase the frequency of bites.
Viruses multiply faster at higher temperatures, which means that a mosquito infected with dengue can spread the infection to the next person more quickly. An increase in water reservoirs, either filled by rain or used to store water during droughts, increases mosquito populations by providing nesting sites.
A recent report by the UN’s Intergovernmental Panel on Climate Change concludes that warming temperatures are expanding geographies favorable for dengue transmission and have contributed to global chikungunya and Zika epidemics over the past decade.
An additional one billion people are projected to be at risk of dengue fever by 2080. In areas already affected by dengue, rising global temperatures could extend the annual transmission season by four months over the next 50 years, increasing the number of cases.
These impacts will be disproportionately felt by countries and communities that are already more vulnerable, have less access to quality health care, and are least responsible for the upstream causes of climate change.
Solutions to mitigate these climate-induced impacts are much needed and within reach. Investments in urban planning, infrastructure, and housing design can reduce mosquito breeding sites and opportunities for human-mosquito interactions.
The current and future threat of mosquito-borne viruses must be placed on the priority list of national and global health agencies. Emphasis should be placed on equipping health systems to diagnose and manage these diseases, strengthening surveillance to detect introduction of mosquitoes and viruses into new areas, and implementing evidence-based and sustainable approaches to mosquito control and disease prevention.
In addition to redoubling efforts to reduce mosquito populations through traditional approaches to chemical control and environmental management, new tools are needed to prevent the spread of dengue. Indonesia recently reached a major milestone by becoming the first country to license a new dengue vaccine for use in both children and adults.
Another new tool is Wolbachia. A symbiotic bacterium found naturally in half of all insect species, Wolbachia inhibits virus transmission when it enters Aedes aegypti mosquitoes. Short-term release of Wolbachia mosquitoes into dengue-affected communities allows Wolbachia to spread to the local mosquito population, effectively “immunizing” it against dengue and other viruses.
This self-sustaining, safe, and cost-effective method has been implemented in 11 countries over the past decade, reaching more than 10 million people, and its efficacy in dengue control has been demonstrated in numerous field trials.
In March 2022, the World Health Organization launched the Global Arbovirus Initiative, which reflects the urgent need for coordinated and sustainable strategies to control dengue and other mosquito-borne viruses. With clear evidence that climate change is accelerating the emergence and spread of these viruses, now is the time to act to support communities and governments in both addressing the root causes of climate change and implementing evidence-based tools to control dengue and other mosquitoes. – communicable diseases.
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