A RARE INFECTION of the central nervous system, primary amebic meningoencephalitis (PAM) is caused by the ameba Naegleria fowleri. PAM is an acute hemorrhagic meningoencephalitis that causes destruction of brain tissue, cerebral edema, and ultimately death.1N. fowleri thrives in water and soil at temperatures from 30° C to about 45° C (86° F to 113° F), and is commonly found in bodies of warm water such as freshwater lakes, warm sources of drinking water, and hot springs. It's not found in bodies of salt water.1,2
Although PAM is rare in the United States, mortality is over 97%.3,4 The best chance of survival rests with prompt recognition and treatment.4 This article reviews the pathophysiology of PAM, diagnostic criteria, and current treatment options.
Between 1962 and 2016, 143 cases of PAM were reported in the United States; of those, only four people survived.1 The worldwide incidence isn't known, but PAM is thought to be underreported and underdiagnosed. Although PAM can occur in individuals of any age, it's been mostly found in younger males, especially children.5
Although found throughout the world, this rare disease is most often associated with warm climates where people frequently work or relax in lakes, ponds, rivers, and pools. According to the CDC, no data on the true risk of PAM are available, and no method has yet been developed to accurately measure the amount of amebic activity in bodies of fresh water.1
Climate change is associated with higher freshwater temperatures, which in turn elevate concentrations of N. fowleri.6 The temperature increase is also associated with increased recreational activity in the contaminated water. Although patients develop PAM primarily after swimming in freshwater lakes and rivers, the infection is also associated with exposure to hot springs and canals and any fresh, untreated water warmed to at least 27°C (80° F).1,7 Because the organism enters the body through the nose, practices that introduce warm water into the nasal passages, such as nasal cleansing with a neti pot, also raise the risk. (See Dangerous waters: Risk factors associated with PAM.)
Infection with N. fowleri occurs when water containing this ameba enters the nose, as during swimming or water sports. The ameba attaches to the olfactory mucosa and migrates to the cribriform plate, a porous bone located at the roof of the nasal cavity. From there it passes into the brain by way of the olfactory bulbs.7,8 (See Nasal anatomy.) Children are more vulnerable to PAM than adults because the cribriform plate is more porous in children.7
Transmission doesn't occur from drinking water that contains N. fowleri, and PAM isn't transmitted person to person.1
Signs and symptoms
Clinical manifestations associated with PAM often mimic those of bacterial meningitis.7 Signs and symptoms appear from 1 to 9 days after exposure to N. fowleri. Patients present with severe headache, high fever, nuchal rigidity, alterations in level of consciousness, and signs of meningeal irritation. In 1 to 12 days after signs and symptoms appear, the disease rapidly progresses to death from increased intracranial pressure and herniation.1,6 Most of the few patients who've survived infection sustained permanent intellectual disability.1 See Signs and symptoms of PAM for two stages associated with disease progression.
Because the disease is rare and the clinical presentation is similar to that of bacterial meningitis, which is far more common, the PAM diagnosis is often delayed or missed altogether.7 If a patient, particularly a child, presents with suspicious neurologic signs and symptoms and has a recent history of swimming in untreated warm water, PAM should be considered in the differential diagnosis. Regardless of patient history, clinicians should also consider testing for amebas in cerebrospinal fluid (CSF) in patients presenting with signs and symptoms of acute meningoencephalitis if other tests have ruled out bacteria and common viruses.2
N. fowleri infection can be diagnosed by detecting the organism, the nucleic acid, or the antigen in CSF, biopsy, or tissue specimens.1 This requires specific lab tests available in only a few labs in the United States. Local or state Departments of Health can direct samples to the appropriate lab for testing. Most cases are definitively diagnosed postmortem.1
Early diagnosis and treatment is essential to give an infected patient any chance of surviving PAM. Current treatment efforts include administering amebicidal medications that can cross the blood-brain barrier, steroids to control cerebral edema, and antiepileptic drugs, if needed, to control seizure activity.1,2,8
The CDC reports that two children who survived PAM infection in 2013 were treated with miltefosine, an investigational breast cancer and antiparasitic drug.1 Adverse reactions to miltefosine include vomiting, abdominal pain, thrombocytopenia, and headaches.
Baig and Khan suggest that administering drugs via the transcribrial route may improve outcomes for patients diagnosed with PAM.8 With this technique, a modified patented intranasal instrument is used to administer medication directly to the cribriform plate, the epicenter of the infection. This route of drug administration may become more common in the future.
Supportive care and patient teaching
Nurses should be prepared to provide emotional support for the family as the likely outcome is poor. Nursing care is primarily supportive and includes the following:9
- Assess vital signs.
- Assess neurologic status and initiate seizure precautions.
- Administer prescribed medications.
- Minimize noise and dim the lights.
- Maintain proper body alignment.
- Protect the patient from hazards of immobility.
- Elevate head of bed to 30°, unless medically contraindicated.
- Assess for and treat fever.
- Provide adequate nutrition and hydration.
- Provide skin care and monitor for pressure injuries.
- Insure adequate cerebral perfusion pressure.
Providers and nurses should be aware that miltefosine is available from the CDC to treat N. fowleri infection. Providers who are treating a patient suspected to have PAM should contact the CDC Emergency Operations Center at 770-488-7100 to consult with an expert.1
Refraining from water-related activities in warm fresh water is the only way to insure PAM prevention. Teach patients who swim to limit the amount of water that goes up the nose and warn them about potentially dangerous practices such as routine nasal cleansing with a neti pot (see PAM prevention).
Dangerous waters: Risk factors associated with PAM
Inadequate sanitation, piping water over land, and unsafe water sources increase the risk of PAM.5 PAM is also associated with the Islamic religious practice of ablution or cleansing before prayer, which may involve nasal irrigation, ayurvedic practices such as “jala neti” or sniffing water and then blowing it out, and practices to provide sinus relief such as routine nasal cleansing with a neti pot.6
The CDC reports that in very rare circumstances, PAM may occur in inadequately chlorinated swimming pools or in tap water heated up to 47° C (116.6° F).1
Signs and symptoms of PAM1
- severe frontal headache
- stiff neck
- loss of balance
- altered mentation
- Avoid getting water up your nose when swimming in warm fresh water. Keep your head out of untreated fresh water or plug your nose if you submerge your head. Don't submerge your head in hot springs.
- Don't perform ritual nasal rinsing with untreated warm water. Use distilled or sterile water or normal saline solution instead. Always rinse and dry the nasal rinsing device thoroughly after each use.
- Avoid activity in fresh water during particularly hot weather.
- Prevent children from digging or stirring up shallow, warm fresh water, submerging their faces, or blowing bubbles while playing in the water.
Centers for Disease Control and Prevention. Parasites—Naegleria fowleri—primary amebic meningoencephalitis (PAM)—amebic encephalitis. 2017. http://www.cdc.gov/parasites/naegleria/index.html.
Seas C, Bravo F. Free-living amebas and Prototheca. UpToDate. 2017. http://www.uptodate.com.
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5. Nicholls CL, Parsonson F, Gray LE, et al Primary amoebic meningoencephalitis in North Queensland: the paediatric experience. Med J Aust. 2016;205(7):325–328.
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8. Baig AM, Khan NA. Novel chemotherapeutic strategies in the management of primary amoebic meningoencephalitis due to Naegleria fowleri. CNS Neurosci Ther. 2014;20(3):289–290.
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Sharma A, Sharma A, Guleria S. Successful treatment of a case of primary amoebic meningoencephalitis: how important is history taking. Indian J Crit Care Med. 2015;19(2):126–127.