A rare, but often deadly, danger lurks within freshwater ponds, rivers and lakes across the United States - and experts say recreational swimmers should be aware.
Iowa officials in early July announced a beach closure at its Lake of Three Fires State Park after a Missouri resident contracted Naegleria fowleri, also known as a "brain-eating amoeba," after swimming there sometime during the end of June.
The person died of a rare and usually fatal brain disease caused by Naegleria fowleri called primary amebic meningoencephalitis, or PAM, Lisa Cox, a Missouri Department of Health and Senior Services spokesperson, told USA TODAY.
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Specific diagnostic tests for the amoeba are available in only a few labs in the U.S., and infections are so rare and tough to initially detect that 75% of diagnoses are made after death, according to the Centers for Disease Control and Prevention. The amoeba infects a person through water up the nose.
After a person in California survived in 1978, reported cases were fatal for 35 years until three children beat infection in the last decade, according to the CDC:
A 12-year-old girl was infected at an Arkansas water park in 2013
An 8-year-old boy survived in 2013, but likely suffered permanent brain damage
In 2016, a 16-year-old boy recovered from infection after a swim in Florida
Here's what to know about Naegleria fowleri.
What is Naegleria fowleri?
Naegleria fowleri is the only species of Naegleria that infects humans and has a 97% fatality rate, according to the CDC. The amoeba is commonly found in the soil and water of warm or hot freshwater, like lakes, rivers, ponds and hot springs. It can also live in water heaters or poorly chlorinated swimming pools, according to the CDC.
The amoeba thrives in temperatures as high as 114.4 degrees Fahrenheit, said Paul Rega, a retired University of Toledo assistant professor of public health, disease prevention and emergency medicine.
"Naegleria fowleri is ubiquitous; it is found in both the freshwaters and soils of six of the seven continents," he said. Rega added that people can also get it from contaminated water on backyard water slides or during artificial whitewater rafting and water skiing.
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The amoeba isn't found in salt water, according to the CDC. "Salt dehydrates cells, so it's like a natural disinfection system," said Christopher A. Rice, an assistant research scientist and Center for Drug Discovery manager at the University of Georgia's College of Pharmacy.
How is climate change impacting Naegleria fowleri's spread?
Naegleria fowleri is often found in freshwaters of southern states like Texas and Florida, two states where the CDC reported 76 cases of PAM between 1962 and 2021. Those cases make up the bulk of reported Naegleria fowleri cases in the U.S.
With 10 cases over over a near 50-year period, California has had the third-highest frequency of reported cases. CDC data shows during that time period, there were 154 reported amoeba cases. All but four were fatal.
Recent cases have been reported as far north as Minnesota and Iowa as climate change raises temperatures of freshwater in northern states, according to Rega's research.
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"Incidence will grow not only because more people could be exposed, but also because it will not be diagnosed in a timely manner due to the naivete of the healthcare profession in many parts of the country," he added.
How does Naegleria fowleri kill quickly?
Naegleria fowleri can make its own nutrients, but still forages soil or water for food from bacteria, fungi and other organisms. That is how problems can arise for freshwater swimmers, Rice said.
If contaminated water goes up a person's nose, the organism migrates to the brain, resulting in an infection with primary amebic meningoencephalitis, he said. Rice added that poor diagnostics and poor therapeutics are why so few people survive PAM.
Naegleria fowleri is often misdiagnosed as bacterial or viral meningitis, Rice said. The illnesses share early stage PAM symptoms like vomiting, fever and nausea. The amoeba can kill within days.
"Patients have succumbed between one day post-symptoms up to between 13 to 15 days post-symptoms," Rice said.
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It can grow and divide within 10 hours, and CDC-suggested therapeutics can take between three to five days after diagnosis to work, Rice said. He explained the amoeba doesn't cause issues when swallowed, as stomach acid will kill it.
How to avoid infection with the brain-eating amoeba?
The key to avoidance is keeping freshwater out of your nose, experts say. The CDC recommends assuming any body of warm freshwater in the U.S. contains Naegleria fowleri.
"Maybe wade through the water rather than splashing in and getting water up your nose," Rice said. If jumping in, holding the nose can help, he added.
Swimmers should avoid immersing their heads under freshwater when swimming or diving, Rega said.
"Good nose plugs would also prevent the amoeba from getting into the nose," he said.
This article originally appeared on USA TODAY: What freshwater swimmers should know about Naegleria fowleri amoeba