Brain Eating Amoeba

Lindee Abe, APRN

It seems that once or twice a year, there is a news story about a brain-eating amoeba where the headline sounds like a science fiction horror movie. To be fair, the infection does sound horrendous and has a high mortality rate. I was familiar with the amoeba from when I went through laboratory technician school, and I distinctly remember it because it was rare and often lethal.

Naegleria fowleri

In 2022, there were two cases in the Midwest. One case involved an adult in Iowa that was believed to be contracted through swimming in a lake. This was determined by testing the lake’s water, which showed the presence of Naegleria fowleri. There was also a child who died in Nebraska after swimming in a local river. Living in the Midwest, this caused quite a bit of news coverage and fear among parents of children who routinely swim in lakes and rivers. This was the first time Naegleria fowleri was found in these states.

There have been cases of Naegleria fowleri infection in previous years in warmer states that made national news, specifically Florida and Texas, but it was generally thought that it was unlikely to occur in colder climates. However, as global warming continues, we have seen more cases of the amoeba further north. Additionally, it has been shown that the cyst stage of the amoeba can survive in colder temperatures (Centers for Disease Control, 2024). There has been a reported cause of Naegleria fowleri as far north as Minnesota in the summer months.

There was also a case in 2023 where a man in Florida was believed to be infected with Naegleria fowleri after using a sinus rinse with tap water. While the cases of Naegleria fowleri tend to make the news because they are tragic and unexpected, the incidence of Naegleria fowleri is still rare. There are typically less than 10 cases of Naegleria fowleri in the United States each year.

Exposure and Transmission

Naegleria fowleri infection occurs when water enters the nose, specifically forceful water up the nose, typically from a freshwater source. Naegleria fowleri can break down mucous, which commonly serves as a line of defense for infection and enters the nasal mucosa. From there, it travels along the olfactory nerve and enters the brain through the cribiform plate (which has small holes) into the olfactory bulb. Once in the brain, Naegleria fowleri will feed on the nerve tissue. There will be a subsequent inflammatory response in the brain that will cause brain swelling. This happens in a few days, resulting in Primary Amebic Meningoencephalitis (PAM).

Symptoms

Symptoms of PAM start with a severe headache, which is understandable considering the pathology. Other symptoms can include fever, stiff neck, sensitivity to light, and confusion. Physical exam may show a positive Kernig sign, positive Brudzinski sign, and tachycardia. These symptoms can also describe bacterial or viral meningitis. Bacterial and viral meningitis are more common and are likely to be thought of first with this presentation. However, any chance of effectively treating the infection is dependent on a timely diagnosis. Several case reports describe patients with PAM initially being thought to have bacterial meningitis without testing to support the diagnosis and starting treatment for bacterial meningitis to have to patient die of PAM.

Diagnosis

Testing for Naegleria fowleri is through cerebrospinal fluid (CSF). Testing for Naegleria fowleri can be done through a polymerase chain reaction (PCR) or Immunohistochemical (IHC) testing. Direct visualization under a microscope is also successful (Centers for Disease Control, 2024). If there is concern for Naegleria fowleri and testing is warranted, the Centers for Disease Control has an emergency number that can be called, and they can walk the provider through testing requirements, specimen shipping, etc. There are also experts available through DPDx at the Centers for Disease Control that can evaluate microscope images for Naegleria fowleri.

Treatment

The fatality rate of PAM is 97% (Centers for Disease Control, 2024). Because PAM is so rare, there is limited study of effective treatment regimens if it is diagnosed promptly. There are only 11 cases of patients that have survived PAM. The effective treatment for PAM has been derived from the case studies of the few survivors and the known effectiveness of medications against Balamuthia mandrillaris and Acanthamoeba spp. Amphotericin B is generally recommended as part of the treatment plan (Grace et al., 2015; Seas & Bravo, 2025). Rifampin has been used with Amphotericin B, along with fluconazole, azithromycin, and miltefosine (Seas & Bravo, 2025).

Prognosis

With a mortality rate of 97% and very few patients that have been successfully treated, the focus has shifted to the prevention of Naegleria fowleri. One area of education for patients is using sinus rinses. Water should be boiled, distilled, or sterile. Education regarding swimming practices can also help to prevent Naegleria fowleri infection, but it is much harder to have patients comply with the recommendations. I grew up in the Midwest, and swimming in lakes was a part of summer, so advising patients not to swim in lakes or rivers, especially kids, is difficult to do.

Prevention

There is a recommendation to use a nose clip or hold your nose if swimming in freshwater and avoid stirring up sediment at the bottom of the lake or river (Centers for Disease Control, 2024). Patients should also be advised to avoid going underwater in hot springs, as last year, Naegleria fowleri was found in hot springs in Wyoming (Centers for Disease Control, 2024). More information has been put out by the state-level health department in many states that have seen cases of PAM due to Naegleria fowleri. There are resources on the Centers for Disease Control website that include posters with more information about Naegleria fowleri that can be hung in exam rooms during the summer. Handouts on safe nasal rinsing practices can be given to patients when nasal rinsing is recommended.

Summary

PAM caused by Naegleria fowleri is a terrifying infection but is thankfully rare. With such a high mortality rate and difficulty diagnosing the infection in a timely manner, patient education and prevention are needed. Providers should also remember the diagnosis when patients present with symptoms consistent with meningitis. While it is not clear if we have been seeing more PAM from Naegleria fowleri due to increased incidence from global warming or better testing and recogniton, it is becoming more common.

References:

Centers for Disease Control. (2024). About Naegleria fowleri infections.

https://www.cdc.gov/naegleria/about/index.html#:~:text=Naegleria%20fowleri%20can%20destroy%20brain,the%20disease%20difficult%20to%20iden4fy.

Centers for Disease Control. (2024). Clinical and Laboratory Diagnosis for Naegleria fowleri Infection. Retrieved from https://www.cdc.gov/naegleria/hcp/diagnosis-tes4ng/index.html.

Centers for Disease Control. (2024). Free living amebic infections. Retrieved from

https://www.cdc.gov/dpdx/freelivingamebic/index.html#:~:text=Naegleria%20fowleri%20does%20not%20form,Figure%20A:%20Cyst%20of%20N.

Centers for Disease Control. (2024). How to Prevent Naegleria fowleri Infec4on When Swimming. Retrieved from https://www.cdc.gov/naegleria/preven4on/swimming.html#:~:text=Avoid%20ac4vi4es%20during%20warmer%20months,naturally%20hot%20(geothermal)%20water.

Grace, E., Asbill, S., & Virga, K. (2015). Naegleria fowleri: pathogenesis, diagnosis, and treatment op4ons. Antimicrobial agents and chemotherapy, 59(11), 6677–6681. https://doi.org/10.1128/AAC.01293-15

Seas, C., Bravo, F. (2025). Free-living amoebas and Prototheca. Retrieved from https://www.uptodate.com/contents/free-living-amebas-and- prototheca?search=Primary%20Amebic%20Meningoencephali4s%20&source=search_result&selectedTitle=1%7E6&usage_type=default&display_rank=1#H13571683.