Yes, you read that right: Brain-eating amoeba have been found in two popular U.S. national parks, according to a recent study from the U.S. Geological Survey, and a number of other institutions, published in the American Chemical Society’s journal, ES&T Water.
Here’s what to know.
What happened?
Researchers took 185 water samples from five popular U.S. national parks, looking at “40 thermally impacted recreational waters” at Yellowstone National Park, Grand Teton National Park, Lake Mead National Recreation Area, Olympic National Park, and Newberry National Volcanic Monument over an eight year period from 2016 to 2024.
What they found revealed widespread detection of Naegleria fowleri (dubbed “brain-eating amoeba”) in 34% of the samples, or 63 specimens, at Yellowstone, Lake Mead, and Grand Teton hot springs and thermally impacted waters. However, the brain-eating amoeba was not found at Olympic National Park or Newberry National Volcanic Monument.
It’s important to note that no infections or deaths due to the brain-eating amoeba have been reported at the detection sites.
What is Naegleria fowleri?
Naegleria fowleri is a free-living amoeba, a one-celled organism that thrives in warm freshwater lakes, rivers, and hot springs. It’s called the “brain-eating amoeba” because it can infect and destroy brain tissue, according to the Centers for Disease Control and Prevention (CDC).
While brain infections caused by Naegleria fowleri are quite rare, they are nearly always fatal, at a rate of 98%.
If water containing the amoeba goes up a person’s nose into the brain, it can cause an infection called primary amebic meningoencephalitis, or PAM. Typically, fewer than 10 people a year in the U.S. get PAM. However, almost everyone who gets PAM dies from it, per the CDC: Out of 167 reported cases of PAM in the U.S. between 1962 to 2024, only four people survived.
Exposure risks
Brain infections caused by Naegleria fowleri usually occur after a person goes swimming or diving in a lake, river, or other fresh water in the summer after a prolonged period when it was hot, causing higher water temperatures but lower water levels.
The CDC cautions you cannot contract the Naegleria fowleri infection simply by swallowing water containing the amoeba, nor can a person pass it to another person.
How to reduce the risk of contracting a Naegleria fowleri infection
The CDC suggests people hold their nose or wear a nose clip if they are jumping or diving into fresh water, and to keep their head above water in hot springs. Don’t dig in shallow water, because Naegleria fowleri is more likely to live there.
Signs and symptoms of a Naegleria fowleri infection
Primary amebic meningoencephalitis (PAM) progresses quickly, with early symptoms that can include headache, fever, nausea and vomiting, stiff neck, confusion, lack of attention to people and surroundings, loss of balance, and hallucinations.
Most people with PAM die within 18 days after experiencing initial symptoms, with many entering a coma and dying after 5 days, per the CDC.