Understanding how changes in climate and land use affect health

Research by Stanford biologist Erin Mordecai and her lab has made startling predictions of how climate and land use changes will shift the burden of disease around the world. In a recent comment published in Nature Microbiology, Mordecai put a fine point on recent years’ unprecedented outbreaks of vector-borne infectious diseases, often in association with climatic and land-use change events, and the urgent need to tackle carbon emissions and deforestation to halt future outbreaks.

“Diseases of the environment, like mosquito-borne, tick-borne, water-borne, and zoonotic diseases, affect billions of people and cause immense and disproportionate health tolls on the most marginalized,” said Mordecai. “These diseases are exquisitely sensitive to environmental change and difficult to eradicate once established.”

Links between climate, environmental degradation, social inequality and disease transmission are complex and often difficult to predict and isolate, Mordecai writes in Nature Microbiology. Using mathematical modeling and empirical work, Mordecai is trying to make such predictions easier. To create more accurate models, Mordecai starts by trying to understand the drivers of change. For example, when mosquitoes experience high temperatures, how exactly does this impact their ability to transmit a pathogen? These mechanistic questions are often answered in controlled lab environments. 

Some vector-borne diseases are already starting to creep higher in latitude and altitude with climate warming, like Lyme disease in the U.S. and Canada, and malaria and dengue in highland Nepal, Ethiopia, and Colombia. In the U.S., endemic vector-borne diseases, like West Nile virus and Lyme disease, could expand with climate warming, according to Mordecai. As the invasive mosquitoes Aedes aegypti and Aedes albopictus become established in large regions of the U.S., they pose a treat for transmitting dengue and Zika. (Read more about Stanford experts working to understand how climate change is impacting the spread of mosquito-borne diseases – and how to respond.)

Analyzing data on vectors and human infections allows Mordecai to understand the environmental conditions leading up to and during infections. When this is done across a large area – such as a country – and time – decades or more – researchers can start to see a clear picture of the environmental and climate conditions that drive disease outbreaks. But infectious disease systems are complex and difficult to observe at large scales for long periods of time. Better data could help predict outbreaks, but there is no silver bullet.

“Each outbreak and disease responds differently to climate and land-use change, so it’s hard to think of a single action that would reduce all of these,” Mordecai said. “At the same time, strengthening health systems and surveillance, investing in equitable and sustainable infrastructure, and protecting the environment could all be policy levers for controlling many environmental diseases.”

Some diseases will likely become more prevalent in the future as vectors, such as mosquitoes, migrate to areas with newly suitable climates for them. But even mosquitoes have their limits. Some regions may even warm past the ideal climate for heat-loving mosquitoes, with potentially complicated consequences for disease transmission. Changes in the habitat can also shift mosquito species composition, for example by favoring the urban-adapted mosquitoes that transmit dengue over the more rural mosquitoes that transmit malaria in sub-Saharan Africa. Taken together, these changes can be nuanced. Yet their consequences are profound, as ecological and climatic changes alter the landscape of infectious disease.

“Halting carbon emissions and deforestation is critical to keep infectious diseases from emerging and spreading,” said Mordecai. “There are so many other consequences of climate and land use change for biodiversity and ecosystems, but it is important to understand just how deeply reliant people are on healthy ecosystems.”

Mordecai is an associate professor of biology in the Stanford School of Humanities & Sciences. She is also a fellow at the Center for Innovation in Global Health, a fellow at the King Center on Global Development, a member of Bio-X, a faculty affiliate at the Stanford Institute for Human-Centered Artificial Intelligence, and a senior fellow at the Stanford Woods Institute for the Environment.

Other Stanford researchers working on challenges at the nexus of climate change and health:

·      Giulio De Leo analyzes factors and processes affecting the dynamics of infectious diseases of humans as well as the dynamics of marine resources of commercial and conservation interest to inform practical management.

·      Desiree LaBeaud studies the intersection of environmental and social determinants of health (climate and poverty) and how they influence risk for vector-borne disease exposure in order to identify and implement community-led prevention and control.

·      Nathan Lo studies the transmission of infectious diseases with a goal of informing public health policy in the U.S. and globally. His international work studies globally important pathogens, such as the parasitic worm Schistosoma, and how changing landscapes of transmission can be harnessed to improve control and elimination prospects.

·      Joelle Rosser investigates mitigation of climate change related health impacts, including how the U.S. healthcare system can prepare for the health impacts of a changing environment and the health impacts of accelerated climate change and wildfires in Alaskan Arctic communities.