Brain-eating amoeba: two recent fatal cases in the United States

The story takes place at a Texas campground . A previously healthy 71-year-old woman is suffering from severe neurological symptoms: fever, headache, and altered consciousness. Four days earlier, to rinse her nose, she repeatedly used a nasal irrigation device filled with unboiled tap water from her camper. Her condition rapidly worsened, with seizures occurring. She died eight days later.

The woman died from a central nervous system infection caused by the amoeba Naegleria fowleri . Analysis of cerebrospinal fluid collected by lumbar puncture confirmed the presence of the amoeba.

Amoebas, which are single-celled infectious organisms that live in soil or water, move by emitting cytoplasmic extensions called pseudopodia.

Naegleria fowleri is named after Malcolm Fowler, who described the disease in Australia in 1965. This amoeba is said to be free-living because it is able to live independently in the environment. If it reaches the brain, it can cause a fatal infection called primary amoebic meningoencephalitis (PAE). Of the 47 species of Naegleria identified to date, only Naegleria fowleri is responsible for PAE.

This amoeba is thermophilic: it has the ability to tolerate temperatures between 18 and 45 °C, with an optimum between 35 and 46 °C. It can survive at temperatures above 50 to 60 °C for short periods. Furthermore, it has been shown that N. fowleri can withstand a wide range of pH, between 2 and 12 (very acidic to strongly alkaline).

During its life cycle, this amoeba can take three forms: trophozoite (active and mobile form), flagellated (equipped with long flagella) and cystic (the amoeba surrounds itself with a protective envelope that allows it to survive while waiting for better conditions). It therefore has the remarkable ability to constantly adapt to its environment, passing from one form to another depending on the circumstances.

N. fowleri is found in moist soils and water. Its geographic distribution is worldwide. This amoeba has been isolated from heated aquatic environments, whether natural or artificial, such as lakes, rivers, ponds, ponds or hot springs. It has also been found in water reservoirs, tap water, hot water from factories or power plants, as well as in insufficiently chlorinated leisure facilities (swimming pools, paddling pools, surf parks).

Naegleria fowleri is capable of infecting the central nervous system by entering through the nasal passages. Acute infection in humans develops when water containing the amoeba is violently inhaled into the upper nasal passages during bathing, swimming, or other recreational activities.

N. fowleri destroys neurons, which is why it is nicknamed "brain-eating amoeba." This expression illustrates the fact that the enzymes and toxins produced by this parasite actively participate in the destruction, literally "digesting," of brain tissue.

More specifically, the amoebas are sucked into the nose and migrate, after attaching to the nasal mucosa, to reach the cribriform plate of the ethmoid bone, located at the base of the skull. This bony structure, perforated with multiple tiny holes, is crossed by the nerve fibers of the olfactory pathways that come together to form the olfactory bulb. N. fowleri then reaches the brain, causing significant damage in the frontal lobe.

Let us return to the case of this septuagenarian patient reported in the weekly epidemiological bulletin (MMWR) of the Centers for Disease Control in Atlanta (CDC, Georgia, United States), dated May 29, 2025.

CDC testing showed that low levels of total chlorine and monochloramine (a disinfectant) in the campground's municipal water system may have contributed to the formation of biofilms, which are thin layers of amoebae that aggregate and adhere to surfaces in prolonged contact with water, such as the inside of pipes, tanks, or RV hoses.

A biofilm can form when water stagnates or disinfectant is depleted, promoting the proliferation of microorganisms. Biofilms also allow for an increase in the bacterial population, which serves as a nutritional resource for free-living amoebae, providing both nutrients to the amoebae and protection against disinfectants.

In the case of the septuagenarian reported by the MMWR, nasal irrigation with tap water remains the presumed route of contamination given, at the time of the samples, the worrying quality of the water from the campsite's municipal network and that of the camper van's tap. However, the bacteriologists did not isolate N. fowleri in the water samples collected. This absence could be explained by the 23-day delay between the use of water for nasal irrigation and the samples being taken and the fact that the environmental conditions were not necessarily identical to those prevailing at the time of infection.

"This case illustrates the importance of maintaining good water quality in RVs and ensuring municipal water systems meet regulatory standards," said Olivia Smith and her colleagues at the Texas Department of Public Health and the CDC.

In March 2025, two months before the publication of this new CDC report, another case of fatal N. fowleri infection was reported in the CDC's Morbidity and Mortality Weekly Report (MMWR) . It involved a 16-month-old child playing in a wading pool. In this water play area, the water is sprayed or splashed onto users, so it is barely or not stagnant. However, it was insufficiently disinfected.

This case dates back to September ¹ , 2023. On that day, this previously healthy baby was hospitalized in an Arkansas hospital. For the past three days, he has had fever, vomiting, decreased appetite, reduced activity, and altered consciousness.

Initial analyses of the cerebrospinal fluid (CSF) revealed nothing abnormal. Similarly, cultures of the blood and CSF samples remained sterile after 24 hours. Unfortunately, the child's clinical condition deteriorated rapidly, suggesting possible intracranial hypertension, a classic complication of meningitis.

Doctors immediately administered standard treatment for bacterial and viral meningitis. The child was admitted to pediatric intensive care for specialized care. A new lumbar puncture was performed, as initial CSF analyses were consistent with bacterial meningitis.

The day after, on September 3, the CSF examination finally revealed the abundant presence of amoebic microorganisms whose morphological appearance evokes the genus Naegleria . It was then that the family reported that the baby had played, on August 26 and 27, two to three days before the appearance of the first symptoms, in a paddling pool and a swimming pool. The child's condition did not improve, he died the next day. Two days later, on September 6, the presence of N. fowleri in the cerebrospinal fluid was detected by PCR analysis.

Numerous health code violations were noted regarding the maintenance of the paddling pool: the pH exceeded 8.2 (the maximum value detected by the monitoring kit), the chlorination system had been out of service for approximately a month, and no daily operational logs were kept. Insufficient disinfection, poor operation, and poor long-term management therefore contributed to the formation of biofilms. Ten days after the death, viable N. fowleri amoebae were detected in a water sample from the paddling pool reservoir.

"This is the third case of primary amebic meningoencephalitis (PAE) associated with a wading pool reported in the United States in four years. In the other three cases, the water was also inadequately disinfected," note Theresa Dulski and colleagues from the University of Arkansas and the CDC. In 2020, 2021, and 2023, three young children died after playing in wading pools.

Several cases of MEAP have also been reported in recent years in connection with a fast-flowing lazy river or surf resort. In 2016, a teenager died after rafting in a lazy river in North Carolina. In 2018, a 29-year-old adult man died after swimming and surfing at a surf resort in Texas.

The distribution of MEAP cases is global, with infections occurring in temperate and tropical countries. They are most often contracted during the summer period, from May to September.

Naegleria fowleri infections are rare but most often fatal: of the 164 cases reported in the United States between 1962 and 2023, only four patients (2.4%) survived.

A death from MEAP was reported in April 2008 in Guadeloupe. This case involved a 9-year-old boy. He became infected while swimming in a popular freshwater pool. Located at the foot of the Soufrière volcano, the pool is fed by geothermal water with a temperature close to 31°C.

The majority of N. fowleri infections occur after recreational exposure to freshwater, such as swimming or diving in lakes in the summer. Cases of MEAP have been reported from various regions worldwide: the United States, New Zealand, China, Pakistan, the Czech Republic, the United Kingdom, Thailand, Korea, Japan, Italy, Iran, Norway, Turkey, Venezuela, Mexico, Costa Rica, Zambia, Australia, Taiwan, France, Belgium, Nigeria, Namibia, New Guinea, South Africa, and Madagascar.

Amoebic meningoencephalitis is a rare disease, affecting fewer than 30 people per year in the United States. Patients described in the literature range in age from 11 days to 75 years.

MEAP most commonly affects healthy adolescent boys during the summer months. However, the youngest known patient to be infected with MEAP was a newborn. In 2020, Turkish pediatricians reported the case of an 11-day-old newborn who developed the condition. Four days before the onset of symptoms, the child had been bathed in water from an unchlorinated well on a summer day. Despite treatment, the infant died at the age of four months.

PAME occurs in healthy children and young adults with normally functioning immune systems. Symptoms typically appear 1 to 12 days after exposure. Clinical diagnosis of primary amebic meningoencephalitis (PAME) is difficult because early signs and symptoms are often nonspecific (fever, headache, vomiting). These clinical signs, sometimes with neck stiffness and seizures, along with cerebrospinal fluid (CSF) analysis results, may suggest bacterial or viral meningitis.

Primary amebic meningoencephalitis progresses rapidly, leading to destruction of brain tissue. The olfactory bulbs and frontal lobe tissue exhibit extensive areas of necrotic and hemorrhagic lesions. This is associated with diffuse acute cerebral inflammation and significant cerebral edema. The latter causes increased intracranial pressure, which can lead to downward displacement of the cerebellum (cerebellar herniation). The severely compressed cerebellum exerts pressure on the brainstem, a structure that controls breathing, heart rate, and other essential functions.

Death occurs within 1 to 18 days after the onset of symptoms, most often after 5 days.

The key to diagnosis is an urgent examination of cerebrospinal fluid. N. fowleri can be identified by direct visualization under a microscope or by using special stains to better visualize these amoebas. Confirmatory tests, PCR or others using antibodies (immunohistochemistry, immunofluorescence) are available in specialized laboratories.

The pathogenic power of Naegleria fowleri is based on several characteristics. This amoeba has a food cup- like structure on its surface, which allows it to suck up and then digest brain tissue. In addition, it secretes various cytolytic molecules (enzymes) that lead to the destruction of the central nervous system. Infection with N. fowleri also triggers an intense immune response, which itself causes brain damage. Furthermore, it appears that N. fowleri has developed strategies to evade the host's immune defenses. In particular, this amoeba is capable of internalizing antibodies attached to its surface, making the immune response less effective.

Swimming or diving in warm freshwater isn't the only way to become infected. Nasal rinsing has recently emerged as a risk factor for primary amoebic meningoencephalitis.

In the United States, 4 cases have been associated with nasal irrigation with tap water, used for health or religious purposes, and at least 14 have been reported in other countries.

Published in 2012, a US study reported the first two fatal cases of MEAP associated with nasal rinsing with tap water using neti pots. They occurred in Louisiana. One of the patients, a 28-year-old man, suffered from chronic allergic sinusitis and irrigated his sinuses at least once a day with a neti pot, using tap water to which he added a salt packet. The other patient, a 51-year-old woman, had sinus problems. She rinsed her nostrils regularly to get rid of dust.

In 2012, doctors in the U.S. Virgin Islands documented a fatal case of primary amebic meningoencephalitis. It involved a man in his forties whose only known exposure to fresh water consisted of using tap water for daily household activities and for nasal rinsing, which he performed several times a day before Muslim prayers. The water used came from two untreated sources: groundwater from a well and rainwater collected in a cistern, both connected to the home's plumbing system.

In 2011, 13 cases of primary amoebic meningoencephalitis due to N. fowleri occurred in Karachi, Pakistan, among young adults. These Muslim patients regularly performed ritual ablution, which involved inserting water into the nostrils. Infection likely occurred during ablutions with tap water. Only two patients survived.

Therapeutic management recommendations are based on drug efficacy results obtained in vitro, in experimental animal models, and from clinical case data detailing the treatments administered to the few patients who survived. The combined use of several drugs may achieve a synergistic effect.

The few people who have survived a MEAP have all benefited from treatment using amphotericin B administered intravenously, sometimes supplemented by intrathecal administration, that is, by injection in the lumbar region so that this drug reaches the cerebrospinal fluid.

MEAP is often treated with a combination of several drugs: amphotericin B, azithromycin, fluconazole, rifampicin, miltefosine, and dexamethasone. Despite these combined treatments, the survival rate remains very low, around 5%.

What can we learn from these clinical cases? First, this formidable infection should be considered in any patient presenting with acute meningoencephalitis and a recent history of possible exposure to fresh water, including recreational water (such as paddling pools or swimming pools). Rapid diagnosis and early treatment are essential to improve the chances of survival.

Finally, it emerges that to reduce the risk of infection, it is essential to follow the recommendations for nasal irrigation, namely using distilled, sterilized or boiled and then cooled water.

To find out more:

Smith OA, Tillman W, Lewis JB, et al. Notes from the Field: Primary Amebic Meningoencephalitis Associated with Nasal Irrigation Using Water from a Recreational Vehicle - Texas, 2024 . MMWR Morb Mortal Wkly Rep. 2025 May 29;74(19):334-335. doi:10.15585/mmwr.mm7419a4

Dulski TM, Montgomery F, Ramos JM, et al. Fatal Case of Splash Pad-Associated Naegleria fowleri Meningoencephalitis - Pulaski County, Arkansas, September 2023 . MMWR Morb Mortal Wkly Rep. 2025 Mar 27;74(10):167-172. doi:10.15585/mmwr.mm7410a2

Eger L, Pence MA. The Brief Case: A Case of Primary Amebic Meningoencephalitis (PAM) after Exposure at a Splash Pad . J Clin Microbiol. 2023 Jul 20;61(7):e0126922. doi:10.1128/jcm.01269-22

iko S, Cope JR, Hlavsa MC, et al. A Case of Primary Amebic Meningoencephalitis Associated with Surfing at an Artificial Surf Venue: Environmental Investigation . ACS ES T Water. 2023 Mar 15;3(4):1126-1133. doi: 10.1021/acsestwater.2c00592

Haston JC, Cope JR. Amebic encephalitis and meningoencephalitis: an update on epidemiology, diagnosis methods, and treatment . Curr Opin Infect Dis. 2023 Jun 1;36(3):186-191. doi: 10.1097/QCO.0000000000000923

Celik Y, Arslankoylu AE. A Newborn with Brain-Eating Ameba Infection . J Too Pediatr. 2021 Jan29;67(1):fmaa100. doi: 10.1093/tropej/fmaa100

Jahangeer M, Mahmood Z, Munir N, et al. Naegleria fowleri : Sources of infection, pathophysiology, diagnosis, and management; a review . Clin Exp Pharmacol Physiol. 2020Feb;47(2):199-212. doi:10.1111/1440-1681.13192

Stowe RC, Pehlivan D, Friederich KE, et al. Primary Amebic Meningoencephalitis in Children: A Report of Two Fatal Cases and Review of the Literature . Pediatr Neurol. 2017 May;70:75-79. doi: 10.1016/j.pediatrneurol.2017.02.004

Siddiqui R, Khan NA. Primary amoebic meningoencephalitis caused by Naegleria fowleri : an old enemy presenting new challenges . PLoS Negl Too Say. 2014 Aug 14;8(8):e3017. doi:10.1371/journal.pntd.0003017

Risk assessment of the presence of Naegleria fowleri amoebae in bathing water . ANSES opinion. Collective expert report. November 2013.

Centers for Disease Control and Prevention (CDC). Notes from the field: primary amebic meningoencephalitis associated with ritual nasal rinsing - St. Thomas, US Virgin islands, 2012 . MMWR Morb Mortal Wkly Rep. 2013 Nov 15;62(45):903.

Yoder JS, Straif-Bourgeois S, Roy SL, et al. Primary amebic meningoencephalitis deaths associated with sinus irrigation using contaminated tap water . Clin Infect Dis. 2012 Nov;55(9):e79-85. doi: 10.1093/cid/cis626

Nicolas M, De Jonckheere JF, Pernin P, et al. Molecular diagnosis of primary amoebic meningoencephalitis in a fatal case in Guadeloupe . Bull Soc Pathol Exot. 2010 Feb;103(1):14-8. doi:10.1007/s13149-009-0028-1