Infectious diseases will seed new ground as the planet warms — here’s where they’ll spread

September 11, 2026 thedigitalsolutioncentre@gmail.com

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Burning Up

As the planet warms, our environment will be transformed, but so will our bodies. In this series, we investigate the health impacts of climate change, focusing on heat, air quality, food and infection risk. We also evaluate the promising solutions that could help us adapt to our warmer future.

published in March, systematically showed that drought conditions could fuel the evolution of antibiotic-resistant bacteria. Most of this resistance is driven by humans’ misuse of antibiotics, which spurs bacteria to evolve genes that help them ward off the drugs. But the Caltech study raised a new worry: As many places face increased drought conditions, climate change itself could act as a selective pressure that could supercharge the evolution of these drug-resistant superbugs.

at their highest for that month since 2017. That trend isn’t a one-off, according to the CDC; as temperatures rise, insects and arthropods can survive longer in the year and farther north.

As a result, vector-borne illnesses such as Lyme disease (spread by black-legged ticks in the Ixodes genus) and West Nile virus (spread by mosquitoes) will become more common in increasingly northerly locations. Already, alpha-gal syndrome, which is not an infection but is transmitted by the Lone Star tick (Amblyomma americanum) and causes an incurable allergy to red meat, is also seeing a dramatic rise as the species expands its range across the Northeast. Positive tests for antibodies to the alpha-gal molecule have increased by 100 times between 2013 and 2024.

Right now, almost half a million people are treated for Lyme disease each year, and the CDC records more than 8,000 cases of other tick-borne diseases annually across the country. It’s not clear how this will change as the climate warms. One 2022 study found major increases in Lyme disease only at levels of warming of 6.3 to 9.9 degrees Fahrenheit (3.5 to 5.5 degrees Celsius) by 2100, but that much warming that fast is now considered an implausible scenario. However, the researchers saw a huge amount of uncertainty in the numbers, given the number of variables that affect whether a spreading tick population will transmit more disease, such as how often people go outside or what steps they take to avoid tick bites. Tick-borne illnesses are likely also underreported, so even the true number of illnesses transmitted each year right now is unknown.

An even more ubiquitous bloodsucker, the mosquito, currently spreads only a few diseases in the U.S. The most common and most serious is West Nile virus, which mosquitoes catch from feeding on infected birds. As of Sept. 8, 504 cases of West Nile virus had been reported in the U.S. in 2026, with 363 of them affecting the central nervous system. And because fewer than 1% of West Nile cases progress to the central nervous system, those numbers likely represent a dramatic underreporting of milder cases, which can cause months of fatigue in some people, in addition to acute flu-like symptoms, such as fever, headache and body aches.

Even though mosquitos love water, climate-related drought could ironically nearly triple the number of human West Nile cases in the U.S. over the next 30 years from around 2,000 reported cases (according to CDC data) to between 5,000 and 6,000. That’s likely because in drier conditions, more mosquitoes are infected, possibly because birds, the intermediate host of the virus, either congregate more closely with mosquitoes around water sources or breed less readily in drought, meaning the fraction of birds that carry the virus is higher than in more water-abundant times.

Mosquito-borne diseases long ago eradicated from the U.S. could also resurge with warming temperatures. The southeastern United States will become more prone to malaria and dengue fever transmission under all levels of warming; summer 2026 saw more than 40 locally-acquired cases of dengue fever in Florida. Public health surveillance and disease-control measures have largely stopped those transmission chains, but the likelihood is that society will have to pour more money into beating these diseases back again in future decades. For example, there are malaria vaccines approved for children, but currently, they are recommended only in areas where the illnesses are endemic. If malaria were commonly found in the southern U.S., millions of Americans might need vaccines, including susceptible adults.

After Hurricanes Matthew and Florence in 2016 and 2018, respectively, North Carolina saw an 11% increase in emergency department visits for gastrointestinal illnesses. Black and American Indian residents were the most affected, likely because discrimination over generations has disproportionately pushed Black Americans and Native Americans to less desirable, more flood-prone land, the researchers found.

Cycles of precipitation, drought and subsequent dust storms can spur the spread of Valley fever, a fungal respiratory disease that causes an estimated 700 to 1,100 deaths per year, mostly in the U.S. Southwest. Valley fever is already on the rise, with cases in Arizona, one of the hotspots for the disease, doubling from about 64 cases per 100,000 people in 2005 to 145 cases per 100,000 people in 2022. As the West warms and dries, Valley fever is likely to spread from its stronghold in the Southwest and become endemic in Idaho, Wyoming, Montana, Nebraska, South Dakota and North Dakota, putting millions more people at risk.

The infectious disease risk from natural disasters tends to stack on top of other health problems stemming from these catastrophes. Flooded buildings can harbor mold that can worsen allergies, asthma and other respiratory illnesses. When major storms cause power loss, people turn to generators for electricity, which release pollutants linked to asthma. Though it’s often hard to track the effects of these disasters, one study found that flooded regions after Tropical Storm Imelda in Texas in 2019 saw 10% more emergency department visits for asthma than nonflooded regions did.

Moreover, the threat to life and livelihood from these disasters can cause mental health conditions, such as post-traumatic stress disorder, Romanello said. The problems compound on each other, she said; already, she has heard reports from Africa about malaria outbreaks, fed by warming, and health workers struggling to reach the affected regions because flooding, also exacerbated by warming, has washed out roads.

As Newman and Shan’s work shows, as spots around the U.S. face new infection risks, existing treatments may become less effective. Their work showed that drought concentrated the natural antibiotics that bacteria make in the soil, making it harder for bacteria susceptible to the compounds to survive. As a result, the microbes with genes for antibiotic resistance did better. The problem for human health is that bacteria are very good at gene swapping, so these soil microbes can easily pass their antibiotic resistance superpowers to bacteria that infect people, their research showed.

A recent study on Salmonella, a bacterium that causes about 1.35 million cases of food poisoning each year in the U.S. alone, found that temperature and rainfall promote antibiotic resistance in this microbe. “Globally, climate change was linked to about a 10% increase in Salmonella resistance gene abundance,” said study first author Zhen-Chao Zhou, an ecology researcher at the Chinese Academy of Sciences in Beijing. Other microbes show similar effects.

Combating the compounding risks requires both public health and climate mitigation approaches, experts say. Not only does the world need to cut greenhouse gas emissions, but people also need to use antibiotics more carefully, Zhou said; improve sanitation practices, such as sewage management, around the world so that antibiotic-resistant strains don’t spread as easily; strengthen food safety; and expand disease surveillance. The public also needs to understand that climate change is a health issue, Romanello said.

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