As climate change alters temperatures and weather patterns around the world, the risk of vector-borne diseases like dengue fever and Zika virus will increase. Here’s what that means for global health and what can be done to limit the damage.
As the climate crisis worsens, millions of people around the world are experiencing the health consequences of extreme weather and climate events such as droughts, floods and heatwaves.
One of the lesser-known consequences is the increased prevalence and spread of bacterial, viral, parasitic, fungal and vector-borne diseases in humans, animals and plants – as well as the likelihood that pathogens that cause diseases will evolve and become resistant to medicines.
This leads to the rise and spread of drug-resistant infections that are difficult or potentially impossible to treat with antimicrobial medicines, including antibiotics, antivirals, antifungals and antiparasitics, and puts modern medicine at risk. For example, common bacterial infections, infections after childbirth or surgery, fungal infections, HIV and malaria, could become harder to treat and increasingly fatal. Millions more lives could be lost each year.
Defined: what are the different types of resistance?
Antibiotic resistance: when bacteria changes in a way that makes antibiotics ineffective.
Antimicrobial resistance: when microbes, such as bacteria, fungi or viruses, change in a way that makes the drugs used to treat them ineffective.
Drug-resistant infections: the illnesses that are caused by resistant microbes, resulting in an infection that is much harder – or potentially impossible – to treat.
How does climate change affect drug-resistant infections?
The climate crisis worsens the threat of drug-resistant infections in several ways. Temperature is intimately linked with bacterial processes and infections. As temperatures warm with climate change, bacterial infection rates may increase and diseases can spread to higher altitudes and latitudes where they were not previously found. Bacteria can also grow and reproduce faster and swap genes with one another (a process called horizontal gene transfer). The faster this occurs, the more likely bacteria are to become resistant.
Higher temperatures may also cause drought, which results in water shortages and a lack of food. This can cause malnutrition, with children most vulnerable, lowering immunity and the ability to fight off infections. Infections can spread quickly in these conditions and could become drug-resistant, with mortality rates likely to increase.
Flooding and drought can lead to displacement, overcrowding and a lack of clean water. Poor sanitation and reduced access to treatment and medicines in disasters like these can cause rises in infections that can become drug resistant.
These extreme conditions, fuelled by climate change, will also put increasing pressure on farmers and livestock producers. Antibiotics are often used in food production and could further increase to protect diminishing crop and animal yields. The overuse and misuse of antibiotics in farming is increasing the development and spread of drug-resistant infections in humans and animals.
How do infections become drug-resistant?
Infections are caused by microbes, such as viruses, bacteria or fungi, which can adapt and evolve in response to their surroundings.
As infection rates increase, attempts to reduce these health threats often result in an increase in the use of antimicrobial drugs, such as antibiotics.
The overuse and improper use of these drugs to treat these infections unnecessarily expose bacteria to these drugs. It gives the bacteria more opportunities to evolve, become resistant to the treatment, survive and spread.
What does the evidence show?
We’re already seeing evidence of how climate change creates environmental conditions where antimicrobial-resistant pathogens can thrive.
The 2022 Lancet Countdown on climate change and health, supported by Wellcome, reports how our climate has become more suitable for disease transmission.
It finds that increased rainfall, heat and humidity are increasing the spread of malaria – a life-threatening disease caused by parasites transmitted to humans via the bites of infected female Anopheles mosquitoes – in regions where it is already present and in new places.
Between 1951-60 and 2012-21, the number of suitable months for the transmission of the deadliest malaria parasite, P. falciparum, increased by more than 30% in the Americas and more than 10% in Africa. P. falciparum has already developed resistance to all antimalarial drugs available in the past 50 years and may become even harder to contain as the climate crisis worsens.
The report also finds that bacteria linked with mild cases of cholera – a diarrheal infection transmitted through ingesting contaminated food or water – is becoming more prevalent as the climate crisis shrinks and contaminates the Earth’s freshwater supply. Between 1982-89 and 2014-21, changes in salt levels in the sea and temperature made more coastline areas suitable for these pathogens to survive and spread.
Waterborne diseases like cholera and typhoid are still a leading cause of human morbidity and mortality worldwide. As climate change increasingly impacts global temperatures and weather events, the risk of these infectious diseases will only worsen. But there are actions we can take to reduce these risks.
In one study, researchers developed a database exploring patterns of drug-resistant bacteria in different climates across 41 states in the US. They found that a 10°C increase in daily minimum temperature was associated with small increases in antibiotic resistance for three common pathogens – E. coli, K. pneumoniae and S. aureus.
In another study, researchers looked to the future and estimated that thawing permafrost in the rapidly warming Arctic could unleash antibiotic-resistant strains of bacteria.
As greenhouse gas levels continue to rise and extreme weather and climate events become more frequent, more human and animal populations will be at risk of drug-resistant infections. And, like other impacts of climate change, the challenge of antimicrobial resistance will disproportionately affect low-income countries that are the least responsible for the crisis.
How big is the threat?
Antimicrobial resistance is already one of the major global health threats of the 21st century. Researchers estimate that 1.27 million people died in 2019 from antibiotic-resistant bacterial infections. And some researchers project this number could rise to 10 million per year by 2050.
Improving diagnostic tests, collecting better data, improving the way we use existing antimicrobials and developing new classes of antimicrobial drugs can help the world to better prevent, treat and control life-threatening drug-resistant infections. But finding and developing these drugs is challenging:
Discovering new antibiotics is a slow and expensive process. They have a high failure rate, and most do not progress to the human clinical trial stage.
Antimicrobial drugs are prescribed sparingly to prevent antimicrobial resistance. This results in lower demand, fewer sales and a small profit for investors.
Existing funding models for these drugs aren’t working. There are many ideas to reform the market, but collaborative action is needed to implement them.
As the climate crisis threatens to compound the existing threat of drug-resistant infections, the need to progress the discovery of new antimicrobial therapeutics becomes even more urgent.
What can be done to help?
The world needs to take action to better understand and tackle these crises through education, research, surveillance, political advocacy and more financing.
To minimise the impacts of climate change on antimicrobial resistance, we need to work to mitigate it. The world, and in particular high-income countries that are the most responsible for the climate crisis and have the most resources to fight it, must transition from using fossil fuels to clean, renewable energy.
Alongside mitigation, there’s a need to implement solutions that can help people adapt to living in a changing climate where diseases are widespread. For example, strengthening our health systems to reduce the burden of disease, supporting new research into the intersections of climate and disease, and investing in the ONE Health approach to share data globally and implement joint responses to health threats.
Governments, the private sector and philanthropic funders must also work together and invest long-term in discovering new antimalarial therapeutics, improving equitable access to treatments for drug-resistant infections and improving the global healthcare infrastructure.
At Wellcome, we're funding research into climate and health and infectious diseases, as well as the underexplored intersection of these two health challenges. We’re also backing innovative partnerships like the AMR Action Fund and CARB-X, which invest in delivering new therapeutics that will diagnose, prevent and treat drug-resistant infections.
Antimicrobial resistance and climate change are intimately linked, and while some progress is being made to tackle both problems, the scale of these crises requires faster action on a larger scale.