The unfolding climate change crisis and mosquito-borne diseases

Following the IPCC's landmark report earlier this month warning of an impending climate catastrophe, on World Mosquito Day, Dr Sarthak Das warns of the potential for climate change to reverse much of the progress made in eliminating mosquito-borne diseases

Dr Sarthak Das
August 20, 2021
The unfolding climate change crisis and mosquito-borne diseases
This photo taken on August 21, 2019 shows a laboratory assistant examining mosquito samples at the Pasteur Institute in the southern Vietnamese city of Nha Trang. Photo: Nhac Nguyen/AFP

On top of its more direct perils, climate change threatens to reverse the remarkable progress the Asia-Pacific has made in recent decades towards eliminating mosquito-borne diseases – malaria in particular. The World Health Organisation has certified China and Sri Lanka as malaria-free and much of Greater Mekong subregion (GMS) – including Cambodia, Laos, Myanmar, Thailand and Vietnam – are tracking well to achieve the same. 

Climate change, however, stands to weaken the region’s ability to fight malaria, and expand the habitat in which malaria mosquitoes thrive. Unless coordinated action is taken, climate change may give malaria the means to stage a comeback and even expand its reach.

This month’s alarming report by the United Nation’s Intergovernmental Panel on Climate Change (IPCC) offers renewed cause for concern. Globally, the report warns, the Earth’s average surface temperature will likely increase by at least 1.5 degrees Celsius in the next 20 years. While temperatures may not rise as dramatically in tropical Asia, the region still faces increased rainfall as the monsoon intensifies, leading to greater flooding, severe heat waves, and humidity. Higher temperatures and heavier rainfall benefit mosquitoes, which breed in stagnant water, particularly the malaria-carrying Anopheles mosquito. 

As insects develop faster in higher temperatures and, as temperatures creep upward across Asia, the Anopheles will inevitably creep along with them into new areas and altitudes. While it’s difficult to pinpoint just where this might occur, the IPCC’s projections suggest that the areas around the Mekong and Indus rivers hold the most promise. The implications for those residing there aren’t encouraging: long before IPCC’s latest report, the World Health Organisation projected that climate change stood to cause an additional 60,000 malaria deaths per year between 2030 and 2050, a potential 15% increase. 

One reason it’s so difficult to know precisely how and where in Asia climate change will have the greatest impact on malaria is because the data linking the two is not only limited but also because the region has made such impressive progress in eliminating the disease in the past two decades. Since 2000, the five Mekong countries have cut malaria cases and deaths by more than 90%, with most cases in Cambodia, Myanmar and Thailand now limited to remote, forest-dwelling communities. 

The strongest connection comes from data collected between 2009 and 2015 in Vietnam. Researchers there found that an increase of 1°C in the maximum temperature appeared to lead to a slight increment of 1.6% in the prevalence of Plasmodium vivax, the most common parasite that causes malaria in the Asia-Pacific. 

That may seem negligible but bear in mind that malaria tends to be concentrated in vulnerable communities living in isolated rural and remote areas with weak health systems. That gives any increase in malaria a potentially outsized impact there. And because disease surveillance in these communities is also weak, new outbreaks can spread unnoticed.

This trend is already evident in the mountainous north-eastern Indian state of Mizoram. While India has seen a steep decline in malaria cases over the past decade, annual cases in Mizoram rose by 40% between 2007 and 2019. Part of this appears to be because nearly half of the state’s residents live in the remote hills, where controlling malaria is more difficult. But part of it could also be due to the approximately 0.8º C increase in average minimum temperatures during the monsoon that Mizoram has experienced over the past three decades, which has made it more suitable for mosquitoes. 

It’s too late to reverse some of the effects of climate change. But it isn’t too late to keep climate change from reversing the progress made towards rolling back malaria

Malaria’s ability to stave off defeat in such battlegrounds is perhaps less troubling than signs the disease is opening new fronts. In the Himalayan foothills of Nepal, for example, malaria-carrying mosquitoes have in recent years been found as high as 2,300 metres above sea level, well above the 1,200 metres they were long known to stay below. Anopheles mosquitoes are also beginning to make an appearance in the highlands of Papua New Guinea. 

Maintaining the region’s progress against malaria – and avoiding a resurgence or outbreak in cases in the face of climate change – will require a whole-of-government response that combines experts not only in health, but also in agriculture, disaster management, infrastructure, meteorology, and water and sanitation. As rising temperatures and rainfall boost the mosquito’s habitat, for example, weather forecasts will play an increasingly important role in predicting where to deploy disease-detection and control efforts and avoid new outbreaks.

The Solomon Islands is among those leading the way. Its Vector Borne Disease Control Programme has developed a malaria-monitoring, early warning system called MalaClim that uses rainfall data from the country’s meteorological service to create a climate-based, malaria risk index that can predict malaria outbreaks. Similarly, the India Meteorological Department and the Indian Council of Medical Research are working together to study the connection between climate and malaria in the eastern state of Odisha, which has one of the country’s highest malaria rates. The meteorological department also issues a bulletin, “Climate Information for Health”, which includes temperature thresholds and disease transmission windows to help authorities forecast and steer off outbreaks. 

Efforts to halt the mosquitos’ march also need to take into consideration local demographics and socio-economic factors. This is especially true when weighing the impact of development projects such as logging, clearing of land for agriculture, mining, and other industrial investments in remote areas where communities have limited access to health services and surveillance systems are weak. Such projects should take into account not only how to minimise their ecological footprint, but also how to ensure they don’t abet the spread of malaria and other mosquito-borne diseases. 

Authorities in the Asia-Pacific region need to respond to climate change by building a resilient healthcare ecosystem, one that coordinates different agencies to devise evidence-based policies for implementing tailored interventions. Experts need to collaborate on ways to harness technological advances to predict new hotspots for mosquito-borne diseases. 

As the IPCC’s report notes, it’s too late to reverse some of the effects of climate change. But it isn’t too late to keep climate change from reversing the progress made towards rolling back malaria’s devastating impact on the lives of countless people in Asia-Pacific. The choice we make now will determine the kind of world this generation – and those yet to come – will inhabit.

Dr. Sarthak Das is Chief Executive Officer of the Communicable Disease Threats Initiative and the Asia Pacific Leaders Malaria Alliance. He is also Adjunct Lecturer at the Harvard Chan School of Public Health. He has spent the last three decades living and working on infectious diseases, health systems in Africa and Asia Pacific.

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