Not the kind of update you want to hear before we head into the busy season for national parks.
When you look at tourism numbers, July through August is when national parks see the most visitors. Makes sense, right? Lots of people are either off work or out of school, and they’ll often use that time to check a vacation destination off their bucket list. The more anxious travelers might think twice about going to a national park after seeing this.
A study published by the U.S. Geological Survey (and its partner agencies) shared that rare, brain-eating amoebas have been found in a number of the most popular national parks in the country – including Grand Teton and Yellowstone. The amoeba, known as Naegleria fowleri, can cause primary amebic meningoencephalitis (A.K.A. PAM), which is almost always fatal.
Researchers say its presence in “thermally impacted recreational waters” is a public health risk:
“Naegleria fowleri is a thermophilic free-living amoeba (FLA) and the causative agent of primary amoebic meningoencephalitis, posing public health risks in warm freshwater environments.
This multiyear, multiagency study surveyed 40 thermally impacted recreational waters across five western United States national parks and recreation areas−Yellowstone National Park, Grand Teton National Park, Olympic National Park, Newberry National Volcanic Monument, and Lake Mead National Recreation Area−to assess N. fowleri presence, concentration, and associated environmental conditions.
A total of 185 water samples were analyzed by qPCR and Sanger sequencing, revealing widespread detection of N. fowleri in 34% of samples with positive detections from Lake Mead, Yellowstone, and Grand Teton hot springs and thermally impacted waters, with concentrations ranging from 4.9 to 115.7 cells/L. Multiple codetections of N. fowleri with nonpathogenic species including Naegleria australiensis were identified, suggesting they may inhabit similar ecological niches in the natural systems in contrast to engineered systems.
These findings indicate that N. fowleri is present in thermally impacted areas across the western United States and underscore the use of enhanced monitoring, public awareness, and risk management strategies in thermally influenced recreational waters.”
Pretty scary, right?
To be clear, PAM isn’t an infection that sees widespread cases every year. According to the CDC, fewer than 10 people are affected by primary amebic meningoencephalitis in the United States each year. That being said, PAM is fatal for almost all that are infected. The study referenced earlier says it has a 98% fatality rate.
The good news is that a) brain infections from PAM are very rare and b) only 167 cases of it have tracked in the U.S. from 1962 to 2024. And the National Parks Service didn’t seem too rattled by the study. An NPS spokesperson basically treated the results of this study as old news, and said that the findings don’t require any sort of nationwide warning:
“These findings are consistent with what’s known about Naegleria fowleri in warm freshwater environments. Infections remain extremely rare, and the study does not prompt any new nationwide warnings. Individual parks continuously evaluate local conditions and will issue visitor advisories or take appropriate management actions if circumstances warrant. Our focus remains on sharing practical steps visitors can take to reduce risk while enjoying the parks.”
In other words, don’t cancel that national park visit you have coming up… but just make sure to be careful if you decide to take a dip.
