August 15, 2025
Case of Primary Amebic Meningoencephalitis Due to Naegleria fowleri Infection in Missouri
Missouri healthcare providers can contact their local public health agency or the DHSS’s Bureau of Communicable Disease Control and Prevention at 573-751- 6113 with questions regarding this Health Advisory.
Summary
- On August 13, 2025, the Missouri Department of Health and Senior Services (MDHSS) announced a case of primary amebic meningoencephalitis (PAM) in a Missouri resident. This is only the third such case in the state since 1983. Two of these cases, including the recently announced case, were locally acquired, and one was acquired when out of state. Testing performed by the CDC laboratories was positive for Naegleria fowleri, the amoeba responsible for PAM.
- The source of the patient’s exposure is currently being investigated by public health officials. Preliminary information implies the patient was involved in recreational water activities at the Lake of the Ozarks days prior to becoming ill.
- PAM is extremely rare. Between 1962 and 2024, there were only 167 reported cases of PAM in the United States. Nonetheless, due to the extremely high death rate of this infection, such cases raise public concerns. This advisory was issued to provide healthcare providers with a background on PAM, as well as a reminder to consider the diagnosis in a patient who presents with fulminant meningitis and recent exposure to freshwater.
- Recreational water users should assume that Naegleria fowleriis present in warm freshwater across the United States; however, infection remains very rare.
Epidemiology
PAM is caused by Naegleria fowleri, a thermophilic, free-living ameba that lives in temperatures above 86°F (30°C) and can tolerate temperatures up to 113°F (45 °C). This protozoan parasite is found in the soil and freshwaters, such as ponds, lakes, rivers, streams, hot springs, and unchlorinated swimming pools. Risk factors for infection include swimming, diving, waterskiing, surfing, and exposure to hot springs. The use of plain tap water for nasal irrigation, instead of the recommended sources of water recommended below, has also been reported as a risk factor for the disease.
PAM is a very rare disease with less than 10 cases reported annually to the CDC in recent years. PAM is more common in warmer regions, such as the southern part of the United States, and generally occurs in the warmer months of spring and summer, possibly due to the increased likelihood of participation in waterborne activities. Prior epidemiological studies revealed the mean age of patients affected by PAM to be 12 years (ranging from 8 months to 66 years); 79% were males. Naegleria fowleri is NOT transmitted from human to human.
Pathophysiology
PAM occurs in healthy young individuals exposed to warm freshwater. Naegleria fowleri infects susceptible individuals when contaminated water enters the body through the nose. Trophozoites penetrate the olfactory mucosa, cross the cribriform plates, and ultimately reach the olfactory bulb and cause the inflammatory reaction and the parenchymal damage associated with PAM. Naegleria fowleri has a 3-stage life cycle: amoeboid trophozoites, flagellate, and cysts. During an infection, Naegleria fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, and occasionally, flagellated forms may be noted in the CSF. Cysts are not seen in brain tissue.
Clinical Presentation
Patients with PAM typically present acutely with fever, severe headache, photophobia, nausea, vomiting, behavioral abnormalities, seizures, and altered mental status. A history of olfactory and taste abnormalities is frequently associated with PAM. Patients with PAM usually have a history of swimming, diving, bathing, or playing in warm, generally stagnant freshwater during the previous 1 to 9 days. On physical examination, meningismus and cranial nerve palsies can be seen. The disease progresses rapidly with increased intracranial pressure leading to uncal herniation and death. The clinical presentation and CSF findings of PAM are very similar to acute bacterial meningitis. Therefore, obtaining an epidemiological history in patients with suspected bacterial meningitis but negative cultures and failure to improve is extremely important. Complications of PAM can include hallucinations, seizures, coma, and death.
In epidemiological studies, the mean time from onset of symptoms to death was 5.3 days (ranging from 1 to 12 days), and the mean time from exposure to death was 9.9 days (ranging from 6 to 17 days). Unfortunately, more than 97% of people with PAM have died from the infection. There have been only five well-documented survivors of PAM in North America.
Testing
Lumbar puncture for cerebrospinal fluid (CSF) analysis is required for the diagnosis of PAM. Laboratory findings suggestive of PAM include leukocytosis with a left shift. The CSF opening pressure is very high. The CSF white cell count ranges from 300 to 26,000 cells/mm with polymorphonuclear predominance. CSF red blood cells are usually seen, and hemorrhagic fluid is seen as the disease progresses. Hypoglycorrhachia and elevated protein are characteristic.
PAM is diagnosed by detecting Naegleria fowleri amebas using different tests offered by only a few U.S. laboratories, including CDC. The tests include polymerase chain reaction (PCR) test that detects Naegleria fowleri in a patient's CSF or tissue, immunohistochemical (IHC) testing and indirect immunofluorescent (IIF) staining that use specific antibodies against Naegleria fowleri to detect the ameba, and direct visualization by examining CSF under a microscope. A definitive diagnosis is made by observation of motile trophozoites on centrifuged CSF wet mount preparation.
Treatment
The optimal treatment of PAM is unknown, with a treatment duration ranging from 9 to 30 days. Considering the fulminant course of the disease and high mortality rates, a combination of drugs is generally used. The drugs found to have antiamebic activity against Naegleria fowleri in the laboratory and different drug combinations used in PAM survivors are available at https://www.cdc.gov/naegleria/hcp/clinical-care/index.html.
Missouri DHSS Recommends:
- Recreational water users should assume that Naegleria fowleriis present in warm freshwater
- Avoid diving and jumping into stagnant freshwater.
- Consider using nose plugs for unavoidable exposures or pinching your nose shut when diving or swimming in freshwater.
- Keep your head above water when swimming in freshwater, hot springs, and other untreated thermal bodies of water.
- When participating in water-related activities, avoid digging or stirring up the sediment.
- Use filtered, distilled, sterile, or previously boiled water for nasal or sinus irrigation, not tap water.
- Physicians who suspect they have a patient with a neurologic infection due to free-living amebae should immediately hospitalize the patient and notify the public health agency for help with case management and specimen submission
- Treatment consultation with infectious disease specialists and/or subject matter experts at CDC is strongly recommended
- Clinicians working in communities with potential exposure to large stagnant bodies of freshwater should play a role in educating patients about the risk and providing information about how to mitigate the risk
References
- Cope JR, Murphy J, Kahler A, Gorbett DG, Ali I, Taylor B, Corbitt L, Roy S, Lee N, Roellig D, Brewer S, Hill VR. Primary Amebic Meningoencephalitis Associated With Rafting on an Artificial Whitewater River: Case Report and Environmental Investigation. Clin Infect Dis. 2018 Feb 01;66(4):548-553.
- Maciver SK, Piñero JE, Lorenzo-Morales J. Is Naegleria fowleri an Emerging Parasite? Trends Parasitol. 2020 Jan;36(1):19-28.
- Graciaa DS, Cope JR, Roberts VA, Cikesh BL, Kahler AM, Vigar M, Hilborn ED, Wade TJ, Backer LC, Montgomery SP, Secor WE, Hill VR, Beach MJ, Fullerton KE, Yoder JS, Hlavsa MC. Outbreaks Associated with Untreated Recreational Water - United States, 2000-2014. MMWR Morb Mortal Wkly Rep. 2018 Jun 29;67(25):701-706.
- Matanock A, Mehal JM, Liu L, Blau DM, Cope JR. Estimation of Undiagnosed Naegleria fowleri Primary Amebic Meningoencephalitis, United States1. Emerg Infect Dis. 2018 Jan;24(1):162-164.
- Burqi AMK, Satti L, Mahboob S, Anwar SOZ, Bizanjo M, Rafique M, Ghanchi NK. Successful Treatment of Confirmed Naegleria fowleri Primary Amebic Meningoencephalitis. Emerg Infect Dis. 2024 Apr;30(4):803-805.
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