What is the treatment for amebic meningitis?

Treatment of Amebic Meningitis

Primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri requires immediate treatment with a multi-drug regimen including amphotericin B, miltefosine, and additional antimicrobials to improve survival chances in this nearly always fatal disease.

Pathogen and Clinical Presentation

• Primary amebic meningoencephalitis (PAM) is caused by the free-living amoeba Naegleria fowleri, commonly found in warm freshwater environments 1
• The clinical presentation mimics bacterial meningitis but does not respond to standard antibiotic therapy for bacterial meningitis 1
• PAM is a fulminant, rapidly progressive infection with mortality exceeding 95% 1
• Symptoms typically begin 10-12 days after exposure to contaminated water and include headache, vomiting, and fever 2

Diagnostic Considerations

• Diagnosis is confirmed in only 27% of cases pre-mortem, making rapid identification critical 1
• CSF examination shows purulent meningitis with ameboid trophozoites visible on wet mount microscopy 3, 2
• The disease should be suspected in patients with meningitis symptoms and recent freshwater exposure, particularly in warm water bodies 4
• If standard bacterial meningitis testing (CSF staining, antigen detection, culture) is negative, wet mount cytology of CSF should be performed to look for Naegleria 3

Treatment Regimen

First-line Treatment

• Amphotericin B is the cornerstone of therapy:
  • Intravenous amphotericin B (conventional or lipid formulation) 3, 2
  • Intrathecal/intraspinal amphotericin B for direct CNS delivery 2

Additional Medications

• Miltefosine has improved survival outcomes when added to treatment regimens 1
  • Two children with PAM survived after treatment with a multi-drug regimen that included miltefosine 1
  • Miltefosine is now commercially available in the USA for this indication 1

Adjunctive Therapies

• Rifampicin has shown benefit when combined with amphotericin B 3
• Other antimicrobials that have been used in combination therapy include:
  • Ornidazole 3
  • Tetracycline 2

Critical Success Factors

• Early diagnosis and immediate initiation of treatment are essential for any chance of survival 1, 5
• PAM should be included in the differential diagnosis for any patient presenting with acute pyogenic meningitis, especially with history of swimming in warm fresh water 6
• Treatment must be started before confirmation of diagnosis if PAM is suspected, as the disease progresses rapidly 4

Prevention Strategies

• Avoid swimming in warm freshwater bodies, especially during summer months 1
• Chlorination of recreational water bodies, particularly after periods of non-use 4
• Avoid nasal exposure during water activities in potentially contaminated water 1
• Cases have been reported from nasal irrigation with contaminated water (neti pots), ritual nasal ablution, and lawn water slides 1

Prognosis

• Despite treatment, prognosis remains extremely poor with mortality >95% 1
• Complications include cerebral edema, myocarditis, diabetes insipidus, and deep coma 2
• Death typically occurs within 5 days of presentation if treatment is unsuccessful 1

Emerging Trends

• Cases have been reported in northern regions where they were previously not present, potentially related to climate change and warming temperatures 1
• The geographic distribution appears to be expanding, with southern US states like Florida and Texas disproportionately represented 5