Jhe death of a child in Nebraska this summer has put the rare but deadly Naegleria fowleri – more commonly known as the brain-eating amoeba – back in the headlines. The amoeba lives in warm fresh water and can enter the body through the nose, where it travels to the brain and begins to destroy tissue.
The case highlighted a troubling new reality – climate change is encouraging the amoeba to appear in areas of the United States where it is not typical, such as the north and west.
Naegleria grows best in warm waters – temperatures above 30°C and can tolerate temperatures up to 46°C, says Charles Gerba, a microbiologist at the University of Arizona. This makes it well suited to propagate in a warming climate.
“It likes warm surface waters during the summer in northern latitudes,” he says.
The amoeba causes a condition called primary amoebic meningoencephalitis, and while getting sick is rare — between 2012 and 2021, only 31 cases have been reported in the United States, according to the Centers for Disease Control — it’s incredibly deadly. According to the CDC, only four out of 151 people survived the infection between 1962 and 2020.
In the USA, Naegleria has generally been restricted to southern states, but in recent years has steadily spread northward. A 2021 study showed that while the rate of infections hasn’t budged, the amoeba is moving from southern states to Midwestern regions. It has been found as far north as Minnesota.
Outbreaks have primarily been associated with swimming in lakes, although an outbreak in Arizona was due to the use of warm groundwater where Naegleria was growing in a well. Previous cases have also shown people contracting the infection from contaminated water used for backyard slides or to perform nasal irrigation.
The pathogen was first discovered in Iowa this summer, after a person died in a popular lake. A nearby weather station recorded high temperatures of around 95°F (35°C) for two consecutive days during the July 4 holiday, when the swimmer is believed to have contracted the amoeba.
Gerba adds that most of the cases are in men under the age of 18 – although the reason is unclear. Young boys may be more likely to participate in activities such as diving in water and playing in sediments at the bottom of lakes and rivers, where the pathogen is likely to reside.
Although amoebas do not cause death, they can cause serious damage. In an alleged Naegleria case in Florida, a teenager developed a fever after swimming in brackish water, and was later hospitalized and suffered a seizure, according to a GoFundMe set up to support his care.
Warmer temperatures not only facilitate the survival and growth of pathogens like Naegleriathey also push people into the water more, which can increase their risk, says Yun Shen, an environmental engineer at the University of California, Riverside.
The climate crisis is also exacerbating extreme weather events – such as floods and droughts – which can introduce more pathogens into the environment. “In drought areas, pathogens will be concentrated in water bodies, which could increase the exposure dose of pathogens when humans are in close contact with water bodies,” Shen explains. In flooded areas, water can transfer pathogens into the environment – for example, a flood could bring pathogens from soil or aquatic environments to homes and buildings, or cause sewage collection to overflow and spit pathogens in the environment.
“In the future, due to climate change, people living in cold regions may also be exposed to warmer temperatures and higher risks of being exposed to pathogens,” Shen says.
Understanding where the pathogen lives is difficult because there is no rapid test for its presence or abundance in a body of water. And even more frustratingly, it’s still unclear why some people get sick with the amoeba and others don’t, according to the CDC. After all, hundreds of millions of people swim in warm, fresh water every year, and only a handful are infected. It is therefore difficult to create acceptable levels to regulate.
As experts continue to observe these changes, Gerba recommends a few precautions for natural freshwater swimming. It is best to avoid putting your head underwater to prevent water from entering your nose in warm freshwater areas. Another option is to wear nose clips, especially for children, he says. Mud and soil in these areas can also become infected, so experts advise avoiding digging or disturbing sediment.
“As surface water temperatures increase further north, we expect more cases in the future,” says Gerba. “I expect this trend to continue.”
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