What to know about the "Brain-Eating Amoeba", Naegleria fowleri

posted on Friday, July 29, 2022 in Water and Land News

Lake of Three Fires Beach, Taylor Co., July 2022Following the death of a Missourian infected after swimming in the Lake of Three Fires last month, the U.S. Center for Disease Control and Prevention, Iowa Health and Human Services, and the Iowa DNR confirmed the presence of Naegleria fowleri, or the “brain-eating amoeba,” in the Lake of Three Fires this week. This is the first death caused by the amoeba that has been linked to an Iowa waterway. Naturally, this news has been raising alarms for recreational water users across the state. 

But what are the risks to Iowans? Naegleria is a genus of amoeba (single-celled organisms) commonly found in warm freshwater and soil. Only one species of Naegleria infects people: Naegleria fowleri

Naegleria fowleri, photo credit: CDCNaegleria fowleri is found around the world. In the United States, the majority of infections have occurred in the freshwaters of southern states but, more recently, cases have begun occurring in more northern states. This is likely due to rising water temperatures associated with climate change. Texas and Florida account for nearly half of the documented infections, but they have  occurred as far north as Minnesota.  

Infections usually occur during the summer months of July, August, and September when it is hot for prolonged periods of time, resulting in higher water temperatures and lower water levels. The amoeba grows best in warm freshwater between 80 and 115 degrees. In the area near Lake of Three Fires State Park, a weather station recorded high temperatures of around 95 degrees on two consecutive days over the July 4 holiday when it’s believed the swimmer contracted the amoeba. 

The amoeba can be found in: 

  • Bodies of warm freshwater, such as lakes and rivers; 
  • Geothermal water, such as hot springs; 
  • Warm water discharge from industrial plants; 
  • Swimming pools that are poorly maintained, minimally-chlorinated, and/or un-chlorinated; 
  • Water heaters; 
  • Soil. 

Kids in swimsuits and life jackets jumping into lakeThere will always be a low-level risk of infection for recreational water users that enter these waters. However, you can only be infected when contaminated water goes up into your nose. The infection cannot be spread from one person to another. You cannot get infected from drinking water contaminated with Naegleria. Naegleria fowleri is less likely to be found in the water as temperatures decline. However, it can still be found in waterbody sediments at temperatures well below where it can be found in the water. Health officials recommend avoiding stirring sediments which may bring the amoeba into the water column.  

Infections happen when water goes deep into someone’s nose and the amoeba is able to travel through the olfactory nerves to the brain. Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue and brain swelling. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis. Initial symptoms of PAM start about 5 days (in the range of 1 to 12 days) after infection and may include headache, fever, nausea, or vomiting. Later symptoms can include stiff neck, confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within about 5 days (range 1 to 18 days).  

The risk of infection is extremely low and occurs most often in children. In the last 10 years, 31 infections from the amoeba were reported in the U.S. Of those cases, 28 people were infected by recreational water, two people were infected after performing nasal irrigation using contaminated tap water, and one person was infected by contaminated tap water used on a backyard slip-n-slide. Compared to the risk of drowning, the risk of contracting the amoeba is very low. In the ten years from 2010-2019, there were almost 4,000 unintentional drowning deaths annually in the US. 

Lake of Three Fires, July 2022Recreational water users should assume that Naegleria fowleri is present in warm freshwater across the United States. It is difficult to assess the risk of infection or prevent infections in any lake because: 

  • Naegleria fowleri occurrence is common; infections are rare. 
  • The relationship between finding Naegleria fowleri in the water and the occurrence of infections is unclear. 
  • There are no rapid, standardized testing methods to detect and quantify Naegleria fowleri in water. 

People can limit their chance of infection by keeping their heads out of the water, plugging their noses before being submerged, or avoiding freshwater altogether when the water temperature is high.  

Swimming in natural waters and pools each have inherent risks. Staying informed, assessing your personal risk, and taking precautions are the best ways to stay safe while recreating.  




  1. beach advisories
  2. climate change
  3. water recreation
  4. water safety