How a Changing Climate Is Reshaping the Spread of Infectious Diseases

As global temperatures rise, the spread of infectious diseases is rapidly evolving in unexpected ways.  That’s something that Dr. Angelle Desiree LaBeaud thinks about a lot. A physician-scientist, epidemiologist and professor in the Division of Pediatric Infectious Diseases at Stanford University’s School of Medicine, LaBeaud studies the epidemiology and ecology of domestic and international arboviruses and emerging infections, including the environmental factors that affect transmission and severity of disease. She is also a senior fellow at the Stanford Woods Institute for the Environment. She spoke with Inside Climate News about the overlooked links between climate, vector-borne illness and health equity—and why localized, community-driven solutions are essential in a more unpredictable world. This interview has been edited for length and clarity.

BHABNA BANERJEE: Climate change is often discussed in terms of rising temperatures and extreme weather, but its impact on human health—especially infectious diseases—is less widely understood. Can you give us a brief overview on how a changing climate is reshaping the spread and intensity of infectious diseases worldwide? ANGELLE DESIREE LABEAUD: When I think about the major categories of infectious diseases that are impacted by climate change, I group them into three big buckets: respiratory, waterborne and vector-borne diseases. For respiratory diseases, there’s always been this idea of “seasonality”—like how there’s a flu season, or a season for other respiratory viruses. What’s interesting is that for many of these viruses, we don’t fully understand why they’re seasonal or exactly how temperature and seasonal changes affect their transmission. But we know they do.  When flooding happens, those pathogens that were sitting in soil or contaminated areas can get swept into the water supply. They move around and people end up exposed, especially during crises when sanitation and access to clean water break down. For the specific diseases I study—vector-borne viral diseases, or arboviruses—climate plays a really significant role. I focus on diseases transmitted by Aedes aegypti, the day-biting mosquito that spreads dengue, chikungunya, Zika and yellow fever. This mosquito loves the heat. So as global temperatures rise, she thrives.  Extreme weather events are also a big factor here. Aedes mosquitoes need water to complete their life cycle—from egg to larva to pupa, it all happens in water. When floods occur, all the discarded plastic and trash lying around fill with water and becomes the ideal breeding ground for mosquitoes. What’s interesting is that these diseases aren’t just associated with floods—they’re also linked to droughts. That might seem counterintuitive at first, but in many parts of the world, people don’t have safe, reliable access to clean water, especially during drought conditions. So they store water in containers that aren’t properly sealed or protected, which too can become the perfect breeding sites for mosquitoes.  BANERJEE: Many vector-borne diseases, such as malaria and dengue, have optimal temperature curves for transmission. How do rising global temperatures create both risks and unexpected declines in disease spread? LABEAUD: It really depends on which disease we’re looking at, and which vector spreads it, to understand how a warming planet will alter transmission and the potential for transmission of these infections.  Mosquitoes, for example, rely heavily on ambient temperature. They’re ectotherms, meaning they depend on room temperature to function. Every vector species has multiple traits that are influenced by temperature. If you map all those temperature-dependent traits, you can build a curve that shows the optimal temperature range for that vector. Depending on where you fall on that curve, if you’re already past the peak and temperatures keep rising, there’s actually the potential for a decrease in transmission risk.

But these systems are highly nuanced. It’s not just about temperature—it’s also about human behavior and how we alter natural habitats. And vectors can evolve, too. So it’s almost like we’re in a race with other organisms to adapt more quickly. BANERJEE: Beyond the ecological and biological factors, how do social determinants—such as migration, urbanization and human-wildlife interactions—shape disease vulnerability? LABEAUD: Infections—particularly vector-borne diseases—are increasingly reemerging and emerging in new areas around the world for a lot of different reasons. Climate change is definitely part of that, with rising temperatures and more extreme weather events like floods and droughts. But the way we live our lives and interact with the environment also plays a huge role. I mean, first and foremost, most of us now live in urban areas rather than rural ones.  And in urban settings, things can get really crowded, sometimes with poor sanitation, which can create habitats for vectors. Unfortunately, we alter the land in so many ways—we deforest, we reforest, we reclaim land, we build irrigation systems and dams. All of these changes, for example, can shift mosquito habitats. We also live in a world marked by ongoing military activity and war, which disrupts disease control and surveillance efforts that might have been in place before conflict began. And then, of course, we move around. A lot of these viruses travel with us.  Say you’re bitten by a mosquito while traveling in a region where the virus is present. Now the virus is in your bloodstream. You might not even have symptoms, but if you go somewhere else and there’s a vector there that can transmit that virus, you can infect local mosquitoes and potentially trigger new outbreaks. That’s how a lot of these infections spread globally; you can now be almost anywhere in the world within 24 hours. BANERJEE: What role does climate change play in the rise of antimicrobial resistance, and how might shifting disease patterns complicate global efforts to manage drug-resistant infections? LABEAUD: The infections I mainly study are mosquito-borne viral infections, and there aren’t any specific drugs available to treat them. The connection I see between antimicrobial resistance and my work actually has to do with plastic pollution.  It turns out that when we were investigating why children were getting sick with fevers, we were also trying to identify where the vectors were breeding. And what we found was that mosquitoes were breeding mostly in man-made plastic containers, in all the plastic trash scattered around the breeding sites. 

We also know that, in communities, all kinds of organisms—including pathogenic bacteria—tend to adhere to plastic surfaces. Just recently, a paper was published about what’s being called the “plastisphere”—all the plastic floating in the oceans, accumulating on the ocean floor and collecting on land. Pathogens can stick to that plastic, come into close proximity with other organisms and potentially share resistance genes. So, the plastisphere can actually be a mechanism for the spread of antimicrobial resistance. BANERJEE: What are some of the biggest challenges for public health systems trying to adapt to these shifting patterns? Are there any existing surveillance or early-warning systems that are proving effective? LABEAUD: We’re facing a lot of challenges. For example, in Kenya, where I can speak from direct experience, we’ve shown that there’s a significant amount of transmission of these infections, but much of it goes unnoticed. Outbreaks happen, but we often don’t realize they’re happening. People get sick without knowing what they’re sick with. There are no targeted antivirals available. Dengue, for instance, is a major killer of children worldwide, and it’s important to know when it’s circulating in your community. That knowledge allows you to launch public health campaigns, reduce standing water and improve healthcare provider awareness. Recognizing dengue and managing it properly—particularly fluid management—can be lifesaving for severely ill children. Right now, most vector control in sub-Saharan Africa is directed toward the malaria mosquito, which is a night-biting mosquito. The primary intervention is the distribution of insecticide-treated nets. But those don’t work against dengue vectors, which bite during the day. So it’s crucial to understand what’s really happening on the ground all over the world. There are, as you mentioned, some early warning systems, especially because of the strong connection between climate and vector-borne disease. Several projects are working to link climate variables with disease outbreaks, to provide policymakers with advance notice so they can allocate resources accordingly. But that’s not easy. We helped develop an early warning system for policymakers in Kenya, but even with good forecasting, if you don’t have the resources to respond, it’s incredibly challenging.  I also think there’s a lot of room for improvement in diagnostics and health care provider training. For example, we still don’t have dengue testing available in most public hospitals in dengue-prone countries. Rapid tests are available, but they’re expensive, only found in private hospitals and often not very accurate. 

“It’s crucial to understand what’s really happening on the ground all over the world.”

So we’re not getting a really good baseline understanding of the burden of disease, or where exactly it’s concentrated in communities. I think expanded access to testing, more healthcare provider education and integrated efforts that link climate with actionable policy outcomes could be beneficial. BANERJEE: Many of the regions most affected by climate-driven disease shifts are also those with the least resources for adaptation. What are some of the most promising community-driven or policy-based interventions you’ve seen? LABEAUD: I’m definitely a community-based researcher, and about three and a half years ago, we launched a nonprofit called the Health and Environmental Research Institute in Kenya. It’s an initiative … that brings together community members, policymakers, scientists and other key stakeholders—because it really takes all of us to do this work. We focus on community action, public education, outreach and activation and awareness-building, while also working closely with policymakers to support and enforce sustainable policies. Our vision is to build environmentally conscious, thriving communities that live sustainably. And we try to achieve that by inspiring collective action—making communities healthier and environments more resilient. Some of the things we do, for example, include large-scale trash pickups. The idea is that by decreasing the amount of plastic laying around our communities, we can reduce the amount of mosquito breeding.  We pair these with other sustainability efforts like tree-planting, and we go into schools to work with children, treating them as the agents of change. We empower them to dump outstanding water and engage in what we call “larval source reduction,” which means eliminating buckets, containers and small pools of stagnant water.  These mosquitoes prefer to feed on humans and don’t fly very far, so keeping your own backyard clean can actually make a big difference. If you’re not breeding mosquitoes on your property, you’re reducing your risk significantly. BANERJEE: As someone working at the intersection of infectious disease research and climate change, what do you think are the biggest knowledge gaps that need urgent attention? Where does research need to go next? LABEAUD: I do think there’s still a lot of potential in early warning systems. We need ones that are co-designed with policymakers, so they’re getting the kind of information they actually need, in a format they can act on, even with limited resources. More integration is really key there. I also think, although these infections are often considered short-lived, they can sometimes have long-term health consequences. So, having effective treatments—actual drugs that target these viruses—would be wonderful. And of course, more vaccines. There are people working on dengue vaccines and chikungunya vaccines, and some are starting to come along. They’re not widely available yet, and some have issues, but vaccines are definitely a promising direction. But I also keep coming back to what we’ve been talking about: community-level work. I really believe there’s so much more we can do locally. Cleaning up the environment, educating people so they understand why they’re doing it and creating a sense of collective responsibility—those efforts go a long way. And it’s a win-win for health. When you clean up your environment, you’re not just reducing mosquito breeding sites and vector-borne disease, you’re also likely reducing things like rodent infestations and food and waterborne illnesses in the neighborhood. It’s not just protection against dengue; it’s protection against everything Aedes aegypti can carry, and beyond. There’s a lot of bang for your buck when you invest in environmental health.

Also, on the topic of emerging infections, there’s this huge link between deforestation and disease. As humans move closer to forest edges and fragment natural habitats, we come into contact with mosquito species—and the pathogens they carry—that we’ve never encountered before.  In pristine, balanced ecosystems, nature regulates itself. You have predators that eat mosquitoes. Things are kept in check. But when we disrupt those systems, we lose that balance. I’m a big proponent of avoiding habitat fragmentation, of thinking holistically. I don’t know if rewilding is exactly the right word, but I do believe in taking a “one health” or “planetary health” approach. These infections don’t just impact us, they affect animals and ecosystems too. We need to be thinking about how we can use nature-based solutions to promote health for humans and for all the other living beings that share this planet.