Brain-Eating Amoeba on Rise in Some U.S. States

Deadly brain-eating amoeba infections are increasing across the U.S. North, and it might be due to climate change.

Researchers from the Ohio Public Health Association described in a case report paper published May 16 in the Ohio Journal of Public Health that infections by the single-celled Naegleria fowleri amoeba have been on the rise in northern U.S. states, particularly Minnesota, Indiana, and Missouri.

"Increased incidence of this rare, deadly, and often misdiagnosed illness in northern states causes concern that N. fowleri is expanding northward due to climate change, posing a greater threat to human health in new regions where PAM [primary amoebic meningoencephalitis] has not yet been documented," the authors wrote.

Naegleria fowleri amoeba
Stock illustration of cerebrospinal fluid containing trophozoites of brain-eating amoeba Naegleria fowleri. This brain-eating amoeba is seeing increasing infections further north in the U.S. ISTOCK / GETTY IMAGES PLUS

The paper described the case study of a woman in her mid-30s from an unspecified Midwestern state that had been infected by the amoeba.

N. fowleri is a single-celled organism usually found in warm fresh water, such as lakes and rivers. It gets into the body via the nose, and can cause a disease called PAM, which leads to severe illness and usually death. Luckily, you cannot get infected via drinking the water.

PAM has a mortality rate of more than 97 percent, the Centers for Disease Control and Prevention (CDC) reported. Just four people out of 154 cases of N. fowleri infection recorded between 1962 and 2021 survived.

"Very rarely it can cause an extremely nasty infection in humans, when it directly invades the brain through the nose, and digests brain cells," Jimmy Whitworth, a professor from the London School of Hygiene & Tropical Medicine, previously told Newsweek.

PAM is similar in symptoms to bacterial meningitis, killing via brain swelling, with N. fowleri also destroying brain tissue.

brain and Naegleria fowleri
Stock image of Naegleria fowleri and the brain. Researchers believe that the rise in infections in northern states may be down to rising temperatures. ISTOCK / GETTY IMAGES PLUS

"It travels to the brain along the olfactory nerve, which is a nerve connecting the nose and the brain that controls our sense of smell," Julia Haston, a medical epidemiologist with the CDC, told Newsweek last year. "Once the amoeba reaches the brain, it begins destroying brain tissue and causes a devastating infection called primary amoebic meningoencephalitis, which is usually fatal."

"The amoebae[...]destroy brain tissue by releasing toxic molecules," Halston said. "The immune system tries to fight the infection by sending immune cells and fluid to the brain. The combination of the toxic molecules and the immune response causes brain swelling and death."

Symptoms usually appear around 12 days after infection, with death following within days. The fatality rate for N. fowleri infections is so high due to the rate that the amoeba reproduces inside the body, and its efficacy at destroying the brain.

"The infected person has no specific, pre-existing defense methods to the amoebae, so they are unable to contain the infection on their own," Bobbi Pritt, director of the clinical parasitology laboratory at the Mayo Clinic, previously told Newsweek. "In the rare instances where people survived, it was because the infection was diagnosed early on, before much damage was done, and they were treated very aggressively."

"The survivors reported to date in the United States were treated with multiple drugs to kill the amoebae, and with therapeutic hypothermia (cooling the body's temperature below normal levels) to reduce brain swelling."

The woman in the Ohio Journal of Public Health paper survived.

cdc map Naegleria fowleri
CDC map of primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri in the United States between 1962–2022. ISTOCK / GETTY IMAGES PLUS

Infections usually occur in southern states like Florida and Texas, but cases have been slowly creeping northwards in recent years, leading researchers to suspect that the range of the amoeba is broadening. Now, the Ohio Journal of Public Health paper shows that the N. fowleri infection rate is indeed increasing further north, and it might be due to climate change.

"Historically, N. fowleri cases in the US have been known to occur in southern states, but recent data indicate an increased incidence since 2010 in northern states such as Minnesota, Indiana, and Missouri," the authors wrote.

"Climate change data indicate consistent increases in surface water temperatures, increasing the likelihood that N. fowleri will pose a greater threat to human health in regions with a history of occurrence and new regions where PAM has not yet been documented."

"Naegleria is only active in warm water, above 30 degrees Celsius [86 degrees Fahrenheit]. It may be expanding its range in response to climate change," Whitworth said. "In the United States, where about three cases per year are diagnosed, it has been reported for the first time in recent years as far north as Nebraska and Minnesota."

The authors warn swimmers to avoid going underwater in freshwater bodies to prevent infection, and to swim in chlorinated water if possible.

"When swimming in fresh water, do not splash or submerge your head. Maintain adequate chlorine concentrations in water distribution systems, especially those with elevated temperatures, to inactivate N. fowleri cysts and trophozoites. If neurological symptoms occur, seek care quickly and report environmental exposures if applicable," they wrote in the paper.

Additionally, the CDC warns against stirring up sediment in shallow, warm fresh water.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about N. fowleri? Let us know via

Editor's pick

Newsweek cover
  • Newsweek magazine delivered to your door
  • Unlimited access to
  • Ad free experience
  • iOS and Android app access
  • All newsletters + podcasts
Newsweek cover
  • Unlimited access to
  • Ad free experience
  • iOS and Android app access
  • All newsletters + podcasts