When most people see a forecast for warm weather, they plan for outdoor activities. Los Alamos National Laboratory scientist Andrew Bartlow says warm temperatures remind him that climate change could boost the danger of disease.
“Climate change is a big thing,” says Bartlow, who studies West Nile virus, Zika, dengue fever, chikungunya, brucellosis, Q fever, Rift Valley fever, and potential pandemic pathogens, such as coronavirus and influenza. “Places get hotter, drier, or wetter—that’s going to shift where diseases are going to pop up.”
Understanding how environmental conditions impact emerging disease and learning how to mitigate disease spread is a key part of Bartlow’s work in biosecurity and biosurveillance. “We’re making sure we can identify pathogens and threats early and quickly so we can have the best possible response,” he says.
In 2021, the World Health Organization issued a report calling climate change “the single biggest health threat facing humanity.” Los Alamos researcher Morgan Gorris, who is studying how weather and climate affect people, agrees with that assessment.
“The effects of climate change on human health are incredibly important because not only do they affect us directly, like exposing us to more extreme heat events or more flooding events, they also have these indirect effects like allowing more disease vectors to flourish or allowing new diseases to inhabit new locations, so people that weren’t exposed to a disease before might become newly exposed to something,” Gorris says. “Climate change is expected to increase the number of disease outbreaks and emerging or new diseases.”
Even a slight increase in temperature can have a dramatic impact on the environment. Researchers have found that climate change is increasing the danger from diseases carried by insects, such as mosquitoes and ticks. Human population growth is also causing people to encroach into animal habitats leading to disease transmission.
“We really need to be aware of things like Chagas disease,” Bartlow says. Chagas is an inflammatory infectious illness once found only in South America, Central America, and Mexico that has now made its way, due to warmer temperatures, to the United States. “The parasite that carries Chagas has already been found in kissing bugs in Texas,” Bartlow says. “That’s scary to me.” Chagas can stay undiagnosed in a patient’s bloodstream for more than a decade before causing heart failure and sudden cardiac arrest.
Modeling a moving menace
Bartlow, Gorris, and their colleagues from the Lab’s infectious disease and Earth systems teams focus on vector-borne diseases, such as West Nile and Zika, which are transmitted by blood-sucking arthropods. The scientists’ goal is to develop projections for how and when insects will move into new geographical areas. “It’s very significant,” says Jeanne Fair, of the Lab’s Biosecurity and Public Health group. “It’s a huge problem for all of us in the temperate regions of the future.”
Infected arthropods transmit pathogens when they bite and feed on people. Fair’s research shows that mosquitoes and ticks are expanding their ranges and carrying numerous diseases into new environments. In recent years, Lyme disease and other pathogens once limited to certain geographical areas have spread across the country. In 2020, the World Health Organization reported that vector-borne diseases accounted for more than 17 percent of all infectious diseases, causing more than 700,000 deaths annually. A 2018 study by the Centers for Disease Control and Prevention showed vector-borne disease in the United States had increased by 300 percent from 2004 to 2016.
Fair’s colleague, Carrie Manore, is an epidemiological mathematician who specializes in modeling mosquito-borne diseases. Manore’s work involves compiling information on how temperature, precipitation, humidity, vegetation, human infrastructure, and other factors affect the way illnesses such as Zika and malaria spread. “Climate change is expected to shift the geographic boundaries of where diseases currently are,” she says. “As temperatures warm, there may be more disease vectors that can start living farther north in warmer habitats; diseases that were once limited to tropical and subtropical areas could now become temperate diseases.”
Manore stresses the importance of collecting data to build accurate mathematical forecasts of how and when these mosquitoes will reach new geographic areas. Preventing disease will only be possible with accurate data, Manore says. “In some cases, we can do a really good job with our forecasting and predicting. And that’s particularly true for diseases where we have good data, like dengue, influenza, and illnesses like COVID-19. There are others where we are limited by data availability. If we have a pathogen that’s kind of rare that we don’t have a lot of data on, the uncertainty around it increases. One of the things we’re working on is encouraging open sourcing of data and working with partners to help us get the data we need to have more certainty.”
Both Fair and Manore say collecting the data, building the models, and tracking the patterns represent essential steps toward disease prevention and protection. “With modeling, you can test mitigations,” Fair says. “Once you have the models coupled, you can look at different scenarios. What if we increased spraying [to kill insects] or irrigated [our crops] differently?”
The models could allow individuals and public entities to adjust accordingly. “You can quantify the risk of certain things,” says Manore. “I can say: Don’t go to this region because this is the hot zone right now, or stay in a house with screens, or wear mosquito repellent,” she notes. “It’s also useful for decision makers and public policy people to say, ‘We are expecting a bad year for Zika, or whatever, and these are the things we can do to impact that risk and hopefully reduce it.’”
Dodging deadly dust
While climate change has some scientists looking at winged sources of disease flying above them, other researchers are focused on the ground. Increasing temperatures and shifting precipitation patterns are predicted to cause a rise in cases of coccidioidomycosis, or Valley fever. The infectious fungal disease lives in the soil and flourishes in warm, dry climates that undergo periodic drenching rains.
The fungi grow during the wet periods, then break apart into tiny spores that travel in dust. When dust and dirt blow or are disturbed and people inhale the spores, the fungus invades their immune systems. The symptoms vary widely, often mimicking pneumonia or lung cancer. The fungus can also attack a person’s skin, bones, nervous system, and brain. People who aren’t killed by Valley fever often require antifungal treatments for the rest of their lives.
Once seen primarily in Arizona and central California, now, in response to environmental changes, Valley fever may spread across the western United States. “Our projections show that the disease may extend all the way north to the United States–Canada border by the year 2100,” says Gorris, who notes that although the number of cases is rising dramatically, awareness of the fungal spore illness remains limited, and many cases go undiagnosed.
“One of my main hopes in studying this disease is to increase awareness,” she says. “A lot of folks haven’t heard about Valley fever, but by raising disease awareness among physicians and health care providers, we may be able to reduce the time to a diagnosis, and reduce the time to start treatment, and hopefully improve disease outcomes.”
In the meantime, Gorris hopes that a global effort to slow climate change will also slow the spread of Valley fever. “There is no feasible way to stop the spread of Valley fever by changing our physical environment because the disease is very interconnected with soils and rodents,” she says. “The only plausible way of reducing the spread is to reduce our greenhouse gas emissions and limit climate change.”
As Gorris works with fellow researchers to forecast the spread of Valley fever, she also collaborates with Los Alamos statisticians and epidemiological mathematicians to investigate other fungal diseases that live in the soil. Histoplasmosis and blastomycosis are two more infections that could spread because of climate change.
“Fungal diseases are something that people don’t talk about much that are pretty terrifying,” Manore says. “Climate change causes cascading impacts that we don’t even anticipate. We live in one giant ecosystem, and if it gets out of equilibrium, it’s going to impact everything.”
Drought, flooding, food insecurity, and unprecedented weather phenomena are displacing people across the globe, leading to widespread migration. According to Bartlow, as climate change drives people to relocate, they are increasingly taking over animal habitats. “Land use has changed from forest to agricultural land and more urbanized areas, and people are encroaching into wildlife habitats. People are going to come into contact with animals and be more exposed to potential pathogen threats.”
Bartlow recalls cases of Hendra virus in Australia. The disease spreads when infected fruit bats urinate and defecate on pastureland where horses graze. The horses become infected and spread the virus to people. Studying diseases that spread from animals to humans, called zoonotic diseases, is an important part of mapping the impact of climate change. “We still need to understand more, and that will help with the modeling and then ultimately mitigation,” Bartlow says. “So I think we’re at the point right now where we know a lot about these things, but we need to do more.”
Gorris echoes these concerns and emphasizes the urgency of this research. “The more humans interact with their natural environment, and the more we expand into undisturbed lands as we’re building out and creating more urban areas, the more we risk these chances of spillover and creating new diseases in the human population.”
But increasingly populated areas aren’t the only places that pose a threat. Thawing arctic permafrost poses yet another reason climate change could lead to disease outbreak. Bartlow says he fears that harmful bacteria and diseases once frozen in the earth are defrosting as temperatures rise. “We’re actually working on some proposals to do biosurveillance in Arctic regions where permafrost is thawing,” he says. “We want to be actively surveilling these areas where things could come out such as anthrax, for example. There have been some outbreaks in Siberia recently that came from bacteria in thawing permafrost that got into reindeer populations and then in humans. It’s a big worry.”
Another worry is diseases that haven’t posed a threat to humans for a century or more. Frozen victims of smallpox and the 1918 flu virus may be buried in the thawing permafrost. “There will definitely be some of these pathogens that are now getting exposed, and potentially some of them may be ones that we haven’t had around in a long time,” Fair says.
Although the threat lurking in thawing permafrost might not be as imminent as that posed by migrating mosquitoes, Bartlow and Fair believe it’s worth investigating. “We don’t really know what’s out there,” Bartlow points out. “Just think of things that could be in there in the permafrost, thawing and then being released. That’s why we want to go up there and actually do active surveillance—so we can be prepared.”
Preparing to prevent pandemics
The desire to prepare for environmental changes and their impacts on disease spread motivates many Los Alamos scientists to continue their research. “The opportunity to work with health officials and epidemiologists to inform folks where these diseases might be a risk makes me feel like I’m contributing to my community and helping,” Gorris says.
Manore agrees, stressing the need for continued research. “Investing in strategic public health research that keeps people healthy by preventing and catching things early is how we reduce mortality and morbidity,” she says. “Our data and models help quantify risk for people and really informs them.”
Part of preparation involves collaborating with scientists around the world. “Diseases do not respect borders,” says Manore, who cooperates with researchers in Ecuador, Brazil, and Mexico.
Bartlow and Fair are working with partners in Georgia, Jordan, Kenya, Tanzania, Rwanda, Uganda, and Ukraine to help researchers in those countries learn how to extract and sequence RNA and DNA to identify pathogens. “Having these systems set up in all parts of the world is super important,” Bartlow says. “We give other researchers the tools, we train them, and we have a shared goal of preventing pandemics. If they identify something, they can do the necessary mitigation strategies in their own countries. But with globalization, things spread much more quickly. We are really trying to understand ecological health security,” he concludes.
Fair says that the COVID-19 pandemic offers a lesson about global interconnection. “A threat anywhere is a threat everywhere,” she notes. “As we have environmental change caused by climate change, then that’s only going to potentially exacerbate the connectedness of threats.”
The scientists also agree that the importance of studying the connection between climate change and disease spread cannot be overstated.
“It may seem funny to think of human health as a national security concern, but it is,” Gorris says. “If we can’t protect the health of our own nation, we create instability and a vulnerable population.”
Fortunately, according to Fair, Los Alamos National Laboratory has access to both the experts and technology to tackle this issue. “When we think of climate change and infectious diseases, a multitude of complex systems come together. Studying really complex systems requires a very collaborative, multidisciplinary effort. It can only be done at a lab like Los Alamos.”
With this collaborative research, the scientists say they have the power to make a difference. Gorris notes that her work offers reassurance that positive change is possible.
“When we looked at the projections of Valley fever in response to climate change, we looked at a high greenhouse gas emission and high climate warming scenario, but we also looked at a moderate greenhouse gas emission and moderate warming scenario. What we found was limiting the amount of greenhouse gas emissions limited the spread of Valley fever. So, ultimately, reducing greenhouse gas emissions could reduce the number of Valley fever cases. And I think that’s a very important point to take home. It’s not all doom and gloom.” ★