The link between climate change and a spate of rare disease outbreaks in 2023

By Zoya Teirstein

A 16-month-old boy was playing in a splash pad at a country club in Little Rock, Arkansas, this summer when water containing a very rare and deadly brain-eating amoeba went up his nose. He died a few days later in the hospital. The toddler wasn’t the first person in the United States to contract the freshwater amoeba, Naegleria fowleri, this year. In February, a man in Florida died after rinsing his sinuses with unboiled water — the first Naegleria fowleri-linked death to occur in winter in the U.S. 

2023 was also an active year for Vibrio vulnificus, a type of flesh-eating bacteria. There were 11 deaths connected to the bacteria in Florida, three deaths in North Carolina, and another three deaths in New York and Connecticut. Then there was the first-ever locally transmitted case of mosquito-borne dengue fever in Southern California in October, followed by another case a couple of weeks later. 

Scientists have warned that climate change would alter the prevalence and spread of disease in the U.S., particularly those caused by pathogens that are sensitive to temperature. This year’s spate of rare illnesses may have come as a surprise to the uninitiated, but researchers who have been following the way climate change influences disease say 2023 represents the continuation of a trend they expect will become more pronounced over time: The geographic distribution of pathogens and the timing of their emergence are undergoing a shift. 

“These are broadly the patterns that we would expect,” said Rachel Baker, assistant professor of epidemiology, environment, and society at Brown University. “Things start moving northward, expand outside the tropics.” The number of outbreaks Americans see each year, said Colin Carlson, a global change biologist studying the relationship between global climate change, biodiversity loss, and emerging infectious diseases at Georgetown University, “is going to continue to increase.” 

That’s because climate change can have a profound effect on the factors that drive disease, such as temperature, extreme weather, and even human behavior. A 2021 study found water temperature was among the top environmental factors affecting the distribution and abundance of Naegleria fowleri, which thrives in water temperatures above 100 degrees Fahrenheit but can also survive frigid winters by forming cysts in lake or pond sediment. The amoeba infects people when it enters the nasal canal and, from there, the brain. “As surface water temperatures increase with climate change, it is likely that this amoeba will pose a greater threat to human health,” the study said. 

Vibrio bacteria, which has been called the “microbial barometer of climate change,” is affected in a similar way. The ocean has absorbed the vast majority of human-caused warming over the past century and a half, and sea surface temperatures, especially along the nation’s coasts, are beginning to rise precipitously as a result. Studies that have mapped Vibrio vulnificus growth show the bacteria stretching northward along the eastern coastline of the U.S. in lockstep with rising temperatures. Hotter summers also lead to more people seeking bodies of water to cool off in, which may influence the number of human exposures to the bacteria, a study said. People get infected by consuming contaminated shellfish or exposing an open wound — no matter how small — to Vibrio-contaminated water. 

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