Naegleria Infection and Primary Amebic Meningoencephalitis (PAM) Treatment & Management

Updated: May 22, 2019
  • Author: Subhash Chandra Parija, MD, MBBS, PhD, DSc, FRCPath; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
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Treatment

Medical Care

Early diagnosis, treatment, and aggressive supportive care hold the only chance for survival in patients with primary amebic meningoencephalitis (PAM). Very few survivors have been reported, with probably no more than a dozen survivors of an estimated 200 cases.

The best described and authenticated case of successful treatment of PAM involved a 9-year-old girl who was diagnosed early in the disease course and was treated with intravenous and intrathecal amphotericin B, intravenous and intrathecal miconazole, and oral rifampin. The patient survived with minimal neurologic sequelae. [23] In addition, the most recent survivor from India, a 25-day-old boy, was successfully treated with the regimen comprising of amphotericin B, rifampicin, and fluconazole for 4 weeks, along with ventriculoperitoneal shunt for obstructive hydrocephalous. The child was free of neurological sequelae at 8-month of follow-up. [2]

The variables in determining the survival likelihood include how early the diagnosis is made and treatment initiated, the infectious dose of amebae, the virulence of the infecting strain, and the health of the patient.

Naegleria species are highly sensitive to the antifungal drug amphotericin B, and it has been used as the core antimicrobial in virtually all cases in which recovery occurred. In a 2017 study, amphotericin B was shown to induce apoptosislike programmed cell death in Naegleria. [41] Minimum amebacidal concentrations of amphotericin B were determined to be 0.02–0.078 µg/mL. Ultrastructural examination of amebae treated with amphotericin B revealed membrane distortions, including the nuclear envelope, rough and smooth endoplasmic reticula, and plasma membrane blebbing.

The macrolide antibiotic azithromycin is effective against Naegleria species in vitro and in murine models, but it has been reported to have poor CSF penetrance. Other antimicrobials that have been tested, mostly in vitro, include clotrimazole, itraconazole, fluconazole, and ketoconazole, with varying degrees of efficacy. Differences in reported drug sensitivities are due to the use of different N fowleri strains in different laboratories, which show variation to drugs. However, amphotericin B remains the drug of choice in the treatment of PAM.

Other drugs that have been evaluated for the treatment of meningoencephalitis due to Naegleria species are miltefosine and chlorpromazine. Kim et al studied the effect of these 2 agents on N fowleri both in vitro as well as in vivo in mice models and compared them with the therapeutic effect of amphotericin B. Chlorpromazine was found to have the best therapeutic activity against Naegleria, both in vitro and in vivo. [42]

In conjunction with the FDA, the CDC has an expanded access investigational new drug (IND) protocol in effect to make miltefosine available directly from the CDC for treatment of free-living amebae (FLA) in the United States. These infections include primary amebic meningoencephalitis (PAM) caused by N fowleri and granulomatous amebic encephalitis caused by B mandrillaris and Acanthamoeba species. [43] All three recent survivors of PAM in the United States (two in 2013 and one in 2016) were treated with miltefosine. [1] Various other agents have been studied in vitro and/or in vivo, including hygromycin, rokitamycin, clarithromycin, erythromycin, roxithromycin, and Zeocin. [44]

Owing to the increasing number of cases being reported and the controversial efficacy of amphotericin B, active research is being carried out to identify newer drugs that are more effective with fewer adverse effects. Recently by using high throughput screening, Debnath et al have identified a novel macrolide, corifungin, with higher activity against Naegleria than amphotericin B. By using in vitro and in vivo animal studies, the authors have demonstrated the superiority of corifungin over amphotericin B. Based on these results, corifungin has been given an orphan drug status by the US Food and Drug Administration for the treatment of PAM. [45]

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Surgical Care

Upon evidence of increased intracranial pressure and possible herniation, emergent consultation with a neurosurgeon is warranted for ventriculostomy.

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Consultations

Consult with an infectious disease specialist early in the course of illness.

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Prevention

The only definite way to evade N fowleri infections is to abstain from water-related activities. [4]

Since N fowleri trophozoites and cysts are susceptible to chlorine, swimming pools should be adequately chlorinated. Case clusters have been reported in association with poorly chlorinated pools. Strongly consider closure of a site if a case of PAM occurs. Warm water is known to be more at risk of harboring these organisms. Thus, avoiding activities in bodies of warm fresh water, hot springs, and water around power plants, which may be thermally polluted, may be advisable. In addition, when taking part in such activities, it would be better to avoid the accidental entry of water into the nose. There are no public health criteria established for what levels of amebae present are acceptable or unacceptable. [46]

People with the habit of using neti pots should use distilled, boiled, or filtered water. The neti pots must be thoroughly washed before and after use. [9]

No vaccine is currently available for the prevention of PAM due to N fowleri. However, owing to the rise in the number of infections, vaccine research is being carried out. Through animal experiments using mice, the efficacy 2 vaccine candidate proteins have been recognized. Intranasal administration of Cry1Ac protoxin along with amoebic lysates has been found to elicit a protective Th2 response against N fowleri infection. [47]  Intraperitoneal administration of recombinant Nfa1 protein has been found to prolong the mean survival time of mice when challenged with infection. [48]

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Further Inpatient Care

Patients with primary amebic meningoencephalitis (PAM) should be monitored in the ICU.

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