When the Climate Shifts, So Do the Pathogens (And So Should We)
One of the seldom-discussed consequences of climate change is the increasing danger around zoonotic disease: infectious diseases that can jump from one animal species to another. While the scientific term zoonoses might not be familiar to the average person, recent history has proven that no one can escape the consequences of viral pandemics. We entered this decade with a world shut down due to SARS-CoV-2, considered a zoonotic disease because of its possible roots in China and Southeast Asian bat populations. The latest virus to break into the general consciousness and spark fear across the world is an Andes strain of the Hantavirus, followed by a resurgence of Ebola in central Africa. Both viruses are zoonotic in nature with high lethality rates. For Americans, the risk posed by these two diseases in particular may feel lower because of the federal government’s ability to isolate cases and halt incoming travel from particular regions. However, Americans are not immune to diseases spread by and between animals. As humans increasingly expand our geographic reach, encroach on untouched natural territories, and interact more closely with animal populations, we will continue to encounter novel zoonotic diseases that pose devastating threats to the human body.
This is a global risk with potential for drastic local consequences. But it is also an opportunity for individual and collective action because the risks associated with zoonotic disease are not limited to the biological effects. Widescale outbreaks and global pandemics cause major global economic disruption. From supply chain issues, to workforce gaps and material shortages, society hinges on the assumption that people can work and any delays are remedied quickly. When these assumptions break down, few are sheltered from the economic and social consequences.
Health Implications of Pathogens in a Changing Climate
It is no secret that our air, water, and soil is being poisoned by human activity and this has health implications. We pump greenhouse gasses into the atmosphere, dispose of harmful chemicals into our waterways, and dump toxins into our soil. These choices will continue to damage environmental and eventually human health. As the population’s general health declines, zoonotic disease becomes easier to spread. Consequently insurance prices will rise to account for the higher frequency in care required for citizens throughout their lifespan. Respiratory illness, waterborne disease, mosquito-borne illnesses, fungal infections, and tick-borne diseases are all predicted to increase with climate change. The sooner we act to address these risks and increase system resilience ahead of time, the better society will fare in the long run.
One example familiar to Americans is habitat changes in the tick genus. Ticks are ectotherms, meaning their bodies don’t maintain a consistent internal temperature, so they are particularly sensitive to environmental temperature shifts. When average temperatures rise, they can expand north into historically colder climates and up into higher elevations. Furthermore, higher temperatures can expedite biological processes, with evidence showing that life cycles can decrease from three years to two. This creates more ticks, which yields a higher likelihood of contact with humans, and a greater risk of vector-borne zoonotic disease spread.
In order for a tick to become an infected vector, it must feed on an animal carrying the bacteria. Scientists believe infrastructure development and fragmentation of forests are contributing to higher rates of infected tick bites. Notably, as forests become smaller due to human activity, rodent predator numbers decrease while rodent populations increase. When rodent numbers rise, so does the likelihood of a tick feeding on an infected mouse. Because habitats are not closed systems, a change for one animal or species will often cause cascading effects for the organisms around them.
Expanding on the issue of mice, which is often mentioned alongside the tick conversation, is how their biological processes are hastening with the changing climate. Conditions like warm autumn, mild winters, and early spring temperatures have afforded mice the potential to yield three additional litters each year. A single mouse can produce 50 to 100 mice a year, and each female can reproduce only six weeks after birth, so further acceleration could trigger exponential population growth. Similarly to the tick example; the more mice you have in an area, the higher the likelihood that infected individuals will come into contact with humans.
Lastly, mosquitos are also vectors for zoonoses. Across the globe, humans have contended with mosquitos spreading disease like West Nile, Dengue Fever, and Malaria. In 1914, the United States Public Health Service (USPHS) received funds from Congress to address malaria throughout the country. Major advancements were made in 1933 with the inception of the Tennessee Valley Authority, which inspired an organized malaria control program. By the 1940s, Malaria Control in War Areas (MCWA) was established to control outbreaks in U.S. military bases and to address infected soldiers returning home. The CDC, established in 1946, stemmed from MCWA, so much of its early work was centered around malaria elimination. In the 1950s, the disease was essentially eliminated in the U.S..
Solutions are Slippery
However, the solutions we prescribe don’t always have the intended effect. Once in a while, a prescription meant to protect humans can be co-opted for personal or economic gain. Other times, communities may realize that a new tool performs far better than those currently in use for things like farming, hunting, and irrigation. In the case of African mosquitos specifically, the mid-2000’s saw nets being transformed from a protective barrier to fishing equipment that far out-performed any of the resources available at the time. This demonstrates how there are tangential consequences of viral zoonoses due to the potential ripple effects that can come from efforts to mitigate their presence.
The zoonotic diseases that humans contend with will increase in frequency, duration, and severity. Studies show a strong correlation between extreme weather, particularly heavy rainfall events, and zoonotic disease outbreak. For example, there is a link between climactic patterns and plague levels in the western United States, with a warmer and wetter climate leading to an increased number of human cases. Additionally, H1N1 influenza virus concentration in the air was substantially higher during the period of Asian Dust Storms (ADS) compared to the normal days, as particulates can get trapped in soil and then spread with high winds. Pathogens have adapted to the changing climate as well, which means they are becoming resistant to conventional treatments. Furthermore, as climates change, diseases that used to be localized to areas like the tropics have spread worldwide. All of this creates a perfect storm for zoonoses to thrive, threatening humans across the globe.
Individual and Collective Action Can Be Proactive and Protective
The potential increased rate and spread of novel and re-emerging diseases around the world is a huge issue to address. To begin, governments across the globe should focus on creating opportunities to reinforce detection and monitoring activities in areas where human-animal interaction is occurring. Particular attention should be paid to historical regions where outbreaks are common.
In Congress, Sen. Baldwin introduced bill S. 4451 that would establish a “Wildlife Health Coordination and Zoonotic Disease Program” jointly administered by the Fish and Wildlife Service and the Administrator of the Animal and Plant Health Inspection Service. According to the bill text, the purpose of this program would be two-fold; first to improve coordination between Federal, State, and Tribal partners on wildlife health issues. Second would be to “support communication, planning, and capacity building efforts to address emerging and ongoing national, State, and regional wildlife health concerns.” Intentional oversight can catch spillover events early, but that isn’t enough for a long term solution.
While we continue to research systems-level environmental and policy prescriptions to address zoonoses as a whole, there are easy behaviors that everyone should adapt to protect themselves from threats at home.
For example, when traveling, investigate all planned excursions that will put you in close proximity to wild animals. Ensure that you, or the tour agency, is aware of any PPE requirements and/or best safety practices. Take precautions seriously at home too. Data submitted through a smartphone app as a part of tick species research found that “people don’t take the same protective measures in their yards as they would if trekking into the woods. Yet while an urban backyard might have fewer ticks overall, there’s still risk.” Protective measures like wearing long pants, applying bug spray, and limiting contact with insects and small animals will reduce risk in your own yard. Little fuzzy friends may be adorable, but that does not mean you should go out of your way to play, touch, or have close contact with them if it can be avoided. Quarantine and seek medical attention if you experience atypical or unusual conditions. Lastly, within your immediate proximity, practice good hygiene practices. Clean your house, don’t touch or pick up stray animals, and make sure you use gloves and proper disinfectants when handling things like animals or animal droppings.
Lastly, citizen science projects and public awareness campaigns are a great place to start educating others and inspiring change locally. Empowering community members to get involved with local government can be the first step.
A great example of community action toward vector-control is happening in my own city of Washington, DC. In March 2026, a simple listserv discussing the mass amounts of mosquitos in the Capitol Hill neighborhood grew into a local task force. Now called the Itty Bitty Mosquito Committee, the group engages in source reduction, community education, native habitat investment, and coordination with city agencies to holistically reduce the mosquito populations in their area without spraying harmful pesticides. They were inspired by a similar program in nearby Maryland; the University Park Community Mosquito Control. While mosquitoes in the U.S. are less likely to transmit dangerous diseases than those found in tropical regions, there are still hundreds of cases of West Nile Virus and Dengue across the country each year. Reducing the mosquito population overall will reduce the number of infected mosquitoes, which lessens the risk of being bitten by an individual carrying a pathogen. Community task forces like these can move the population toward a goal without the institutional barriers and costs associated with traditional governmental routes. Zoonotic diseases may be on the rise but we have the tools and knowledge to reduce some of the risks.
As humans expand our geographic reach, encroach on untouched natural territories, and interact more with animal populations, we will encounter novel zoonotic diseases that threaten the human body. The sooner we act to address these risks, the better.
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