Abstract

BackgroundBrain infection by free-living amoebae can present as granulomatous amoebic encephalitis if caused by Acanthamoeba spp. or Balamuthia mandrillaris, or as primary amoebic meningoencephalitis if caused by Naegleria fowleri, the latter with high morbidity and mortality. Diagnosis is made by studying cerebrospinal fluid or tissue samples by direct microscopy, culture, polymerase chain reaction, or immunofluorescence. There is no specific treatment, and there are only reports of success with prolonged use of combined drugs.

Cases DescriptionWe present five cases with a diagnosis of brain infection by free-living amoebae treated at the Hospital Almenara. The patients received surgical treatment, and four of them also received antiparasitic treatment; in one case, the diagnosis was post-mortem. Antiparasitic treatment consisted of a combination of miltefosine, voriconazole, and albendazole mainly, with an average time of 4.8 months. All cases were diagnosed after the initial surgery, and two patients died. Diagnosis in all cases was by direct microscopy, but typing of the free-living amoeba involved was not possible.

ConclusionBrain infection by free-living amoebae is a disease with high morbimortality, which requires early diagnosis for a better prognosis if long-term combined treatment is established.

Keywords: Amoebic encephalitis, Central nervous system protozoal infections, Free-living amoeba, Meningoencephalitis, Subdural empyema (source: MeSH-BIREME)

INTRODUCTION

Brain infection by free-living amoebae is a rare disease with high mortality. On the South American continent, a significant number of clinical cases have been reported in which the majority (~95%) of patients did not survive.[ 4 , 14 ] Brain infections usually originate from an external source, such as the ears, nose, throat, skin, or others. Migration of free-living amoebae into brain tissue can present as granulomatous amoebic encephalitis (GAE) or primary amoebic meningoencephalitis (PAM), which have distinct clinical courses and different etiologic agents. The former is usually caused by Acanthamoeba spp. and Balamuthia mandrillaris, while the latter is caused by Naegleria fowleri.[ 14 , 20 , 21 ]

One of the greatest challenges in medicine is to diagnose free-living amoebae. This requires clinical suspicion, patient risk factors, laboratory expertise, and molecular biology tools. Diagnosis is made on samples of cerebrospinal fluid (CSF), secretions, or tissues obtained premortem or postmortem. Diagnostic tests include microscopy, culture on Gram-negative enriched agar or axenic culture, polymerase chain reaction (PCR) molecular tests, direct immunofluorescence (DIF), or immunohistochemistry.[ 14 ]

There is no specific treatment for these infections. However, several treatment schemes have allowed the recovery of some patients; these include the combination of drugs for prolonged periods. In Peru, there are some reports in which drug combinations were used, including amphotericin B, miltefosine, voriconazole, itraconazole, fluconazole, and albendazole.[ 11 , 12 , 17 ] The international literature also reports the inclusion of drugs such as azithromycin, rifampicin, moxifloxacin, meropenem, and linezolid, among others.[ 12 , 15 , 17 , 19 , 23 ]

Because it is a pathology with low frequency and high morbimortality, it becomes a diagnostic challenge when signs and symptoms are present that can manifest in many more common diseases, and there are no risk factors; we present this series of five cases treated in our service in the past 5 years.

CASES DESCRIPTION

The database of patients attended from December 2019 to June 2024 in the Vascular, Tumor, and Functional Neurosurgery service of the Hospital Nacional Guillermo Almenara Irigoyen was reviewed, and five patients with the diagnosis of brain infection by free-living amoebae were obtained, of which the epidemiological, clinical, diagnostic, and treatment data are described.

Two patients had a history of contact with stagnant water (ponds and swimming pools), the other three patients had no risk factors for the development of brain infection by free-living amoebae, and another two patients had mild cranial trauma (without cutaneous or bone continuity solution). In addition, all our patients were immunocompetent and were children. The remaining epidemiologic and clinical data are summarized in Table 1 .

Table 1:

Epidemiologic and clinical data of patients with free-living amoebic infections.

Two patients presented as juxtadural empyema, two patients had brain abscesses, and one patient presented as meningitis, the latter undergoing surgery for communicating hydrocephalus. On admission, computed tomography (CT) scan, severe diffuse edema was seen in three cases and moderate diffuse edema in two cases, with a median midline shift of 5.4 mm (Interquartile range [IQR]: 4.75–6.80 mm).

In all cases, the diagnosis was made after surgery by direct visualization of mobile structures compatible with free-living amoeba trophozoites [ Figure 1 ] without achieving genus and species typing because we did not have the necessary laboratory supplies. The samples where the parasitic structures were found were CSF in two patients, brain abscess secretion in two patients, and subdural empyema secretion in one patient. Of those that were brain abscesses, one patient had an occipital location, and one patient had a temporal location [ Figures 2 and 3 ].

Figure 1:

Free-living amoeba trophozoites under a microscope 40× (arrow). (a) This is a sample from one of the deceased patients who presented with a left temporal abscess. (b) This is a sample from one of the surviving patients who presented with subdural empyema.

Figure 2:

A 9-year-old female patient with a history of mild head trauma was admitted with 20 days of symptoms due to headache, fever, and vomiting; with direct microscopy of cerebrospinal fluid showing amebiasis, they underwent evacuation of epidural empyema, with torpid evolution, development of intracerebral abscess, ventriculitis, septated hydrocephalus, finally dying despite treatment. (a) Non-enhanced brain computed tomography (CT) scan showing hyperdense epidural collection (thin arrow), associated with a hypodense lesion in the right frontal lobe (thick arrow). (b) Enhanced brain CT scan showing a heterogeneous epidural collection with contrast enhancement in the lower part (thin arrow), associated with intense enhancement of the underlying meninx (arrowhead), with a hypodense lesion in the right frontal lobe that does not enhance (thick arrow). (c) Non-enhanced brain CT scan showing total evacuation of epidural empyema but the persistence of the right frontal hypodense lesion (thick arrow), but in smaller volume, and with the restoration of the right frontal horn of the lateral ventricle. (d) Enhanced brain magnetic resonance imaging (MRI), which shows a right frontal lesion with ring enhancement (thick arrow), with liquid content inside but with precipitated content of greater intensity (thin arrow), compatible with right frontal abscess, in addition to ependymal enhancement (arrowhead) and hydrocephalus, which could indicate ventriculitis. (e) MRI diffusion sequence, showing a right frontal lesion that restricts in the periphery (thick arrow) and precipitated material in the lower part (thin arrow), compatible with brain abscess, as well as a restriction in intraventricular content in the occipital horns (arrowhead), compatible with pioventriculitis.

Figure 3:

A 9-year-old male patient with a history of mild cranial trauma was admitted with 12 days of disease with headache, fever, and vomiting, for which he underwent a craniotomy plus biopsy of the left temporal lesion, showing amebiasis under direct microscopy, whose result arrived after the patient’s death. (a) Non-enhanced brain computed tomography (CT) shows diffuse hypodense lesions at the left frontal (thin arrow), right frontal (arrowhead), and mainly at the left temporal level (thick arrow), which collapses the basal cisterns. (b) Enhanced brain CT shows an extensive hypodense lesion that goes up to the right frontal lobe (arrowhead) but is mainly located in the left temporal lobe (thick arrow), which does not enhance but generates arachnoid enhancement at the level of the Sylvian fissure (thin arrow). (c) Postoperative non-enhanced brain CT scan showing persistence of the lesion, with pneumocephalus (thin arrow) at the biopsy site. (d) Postoperative enhanced brain CT shows the persistence of the lesion that does not enhance, with pneumocephalus (thin arrow) at the biopsy site.

On the results of CSF studies, it was evidenced that of the two patients who were diagnosed in CSF samples, none had pleocytosis, one had a low glucose level of 23 mg/dL, and both had mildly elevated protein level (66 mg/dL and 84 mg/dL). Of the other three patients, two had no pleocytosis, two had low glucose levels (21 and 29 mg/dL), and two had elevated protein levels (>300 mg/dL and 153 mg/dL).

Four patients received treatment with miltefosine plus voriconazole and albendazole, with a median time of 130.5 days (IQR: 91.25–205.75 days). In one patient, the diagnosis was postmortem. Two patients required a ventriculoperitoneal shunt system, two patients underwent craniotomy and brain abscess resection, and two patients underwent craniotomy and evacuation of juxtadural empyema, but of the latter group, one patient ended in decompressive hemicraniectomy.

Regarding their evolution, of our five patients, two died, and the other three were discharged with an average hospitalization time of 4.6 months, with and modified Rankin scale (mRS) of 2. At follow-up, two patients had an mRS of 0, with an average follow-up time of 29.3 months. The other patient developed medulloblastoma, decreasing his mRS to 4, with a follow-up time of 12 months. Furthermore, of the two patients who died, one died after 7.2 months of hospitalization due to infectious complications, while the other patient died on the eleventh postoperative day due to intracranial hypertension.

DISCUSSION

This study aims to describe the characteristics and evolution, as well as the management of five patients we had in our service with brain infection by free-living amoebae, in whom the diagnosis was complicated, and two of them died, which shows that this disease has a high mortality rate. In addition, it should be mentioned that in our department, we have treated 110 patients in the last years with neuroinfections, with free-living amoeba infection accounting for only 4.55% of these.

Acanthamoeba spp. and B. mandrillaris cause GAE, which is more of a subacute or chronic infection, while N. fowleri causes PAM, which is an acute disease.[ 14 , 20 , 21 ] Infection by these parasites has generated increased scientific interest because <5% of patients survive.[ 14 , 20 , 21 ]

N. fowleri has a nasal route of infection, contacting the olfactory neuroepithelium, then going to the olfactory bulb and ending up in intimate contact with the frontal lobe. In Peru, there is only a single record of a possible case of N. fowleri, which has not been typified,[ 1 , 11 ] while Acanthamoeba spp. and B. mandrillaris are disseminated through the vascular walls (lamina propria) and, therefore, can end up in the frontal, parietal, temporal lobe, or any other territory.[ 20 , 21 ] In our series, four cases are presented as juxtadural empyema or brain abscess, with the location of the subdural space, epidural space, occipital lobe, or temporal lobe.

It is typically described that Acanthamoeba spp. mainly affects immunocompromised individuals; however, this is not entirely correct because it will depend on the genotype, the (hypothetical) parasite load, exposure to a contaminant source, and the host’s decreased immune status. While N. fowleri and B. mandrillaris are immunocompetent individuals, this is not always correct.[ 2 , 20 , 21 , 23 ] In our series of cases, all our patients were immunocompetent, and we have not been able to establish with certainty whether they had any risk factor, although two patients had a history of contact with stagnant water; however, there is no typing of the species involved.

According to Nicholls et al., this pathology primarily affects young male patients who have been exposed to freshwater recreational sites in southern states,[ 13 ] as in our study, all patients were of pediatric age, and the majority were male, which corresponded to three patients in our study.

It is described that imaging studies in GAE show one or multiple lesions, well-defined, with ring contrast uptake and perilesional edema, and when there is meningeal involvement, additional leptomeningeal contrast enhancement is seen. In the case of PAM, the images do not show specific findings and may be normal, or with diffuse cerebral edema, signs of endocranial hypertension and meningeal enhancement at basilar level, hydrocephalus, ischemic lesions at different levels, and even white matter involvement.[ 8 , 18 ] In our case series, two patients had a subdural hemispheric hypodense collection, and another two patients had a lesion with ring contrast enhancement at the temporal and occipital lobes, suggesting PAM and GAE, respectively, as seen in Figures 2 and 3 .

For the diagnosis of Acanthamoeba spp., direct detection of the parasite in CSF, either by microscopy, parasite culture, or PCR, or detection of the parasite in brain biopsy by microscopy, parasite culture, PCR or immunofluorescence (DIF) can be used. Of these methods, the most frequent were CSF culture and microscopy.[ 14 ] For the diagnosis of B. mandrillaris, CSF samples are used, diagnosing by PCR and parasite detection by biopsy using microscopy, PCR, or DIF. Of these, microscopy and the use of DIF in biopsy were the most frequent.[ 14 ] In the case of diagnosis of N. fowleri, CSF was diagnosed by microscopy, culture, or DIF, with microscopy or DIF in CSF being the most frequent.[ 14 ] In our case series, we were unable to typify the genus and species of the free-living amoeba, but in all cases, we were able to identify some free-living amoeba under direct vision by microscopy in different types of specimens obtained during surgery.

Amphotericin B deoxycholate, rather than liposomal, is used in PAM because it is effective against N. fowleri, but not against Acanthamoeba spp. and B. mandrillaris.[ 7 , 14 , 16 ] For N. fowleri, it has been shown that in experimental animal studies, a survival rate of 40% is achieved when using amphotericin, 75% when using chlorpromazine, and 55% when using miltefosine.[ 9 , 23 ]

Miltefosine has better results concerning bioavailability and its interactions with other drugs. On the other hand, most azoles and macrolides are amoebostatic rather than amoebicidal. However, their penetration of the blood-brain barrier and their nephrotoxic and hepatotoxic effects should be assessed for rational use of antiamebic therapy.[ 5 , 10 , 14 ]

For GAE, several drugs can be used alone or in combination, such as voriconazole, fluconazole, itraconazole, rifampicin, meropenem, linezolid, liposomal amphotericin B, trimethoprim/sulfamethoxazole, moxifloxacin, caspofungin, and miltefosine, but they are effective only in early stages.[ 15 , 19 , 23 ]

There are studies in Peru with patients who have survived but with long-term therapy (6 months) with albendazole and itraconazole or with itraconazole plus albendazole plus amphotericin B.[ 12 , 17 ] Well, in our case series patients, once the diagnosis was confirmed, received miltefosine plus albendazole plus voriconazole with a median treatment time of 130.5 days (Interquartile range: 91.25–205.75 days), although only one patient died before his positive result for brain infection by free-living amoebae.

In addition, according to Vollmer and Glaser, in their case report of a survivor of free-living amoeba infection, other case reports account for a total of eleven survivors out of 200 case reports. Although a comprehensive neurological evaluation is not described in most cases, they mention that most had a good outcome without significant neurological sequelae.[ 3 , 6 , 12 , 15 , 22 ] These results are like ours, where three patients had good discharge outcomes with an mRS of 2.

CONCLUSION

Brain infection by free-living amoebae is a disease with high morbimortality, which becomes a diagnostic challenge because other etiologies are thought of before this type of infection, but if diagnosed early, it has a better response to multiple antiamebic therapies.

Ethical approval

The Institutional Review Board approval is not required.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Cabello-Vilchez AM. Naegleria fowleri in Central and South America: The brain-eating amoeba is it in Peru?. Rev Cuerpo Med HNAAA. 2023. 16: e18888

2. Callicott JH. Amebic meningoencephalitis due to free-living amebas of the Hartmannella (Acanthamoeba)-Naegleria Group. Am J Clin Pathol. 1968. 49: 84-91

3. Cary LC, Maul E, Potter C, Wong P, Nelson PT, Given C. Balamuthia mandrillaris meningoencephalitis: Survival of a pediatric patient. Pediatrics. 2010. 125: e699-703

4. Deetz TR, Sawyer MH, Billman G, Schuster FL, Visvesvara GS. Successful treatment of Balamuthia amoebic encephalitis: Presentation of 2 cases. Clin Infect Dis. 2003. 37: 1304-12

5. Diestel A, Roessler J, Berger F, Schmitt KR. Hypothermia downregulates inflammation but enhances IL-6 secretion by stimulated endothelial cells. Cryobiology. 2008. 57: 216-22

6. Doyle JS, Campbell E, Fuller A, Spelman DW, Cameron R, Malham G. Balamuthia mandrillaris brain abscess successfully treated with complete surgical excision and prolonged combination antimicrobial therapy. J Neurosurg. 2011. 114: 458-62

7. Ferrante A. Comparative sensitivity of Naegleria fowleri to amphotericin B and amphotericin B methyl ester. Trans R Soc Trop Med Hyg. 1982. 76: 476-8

8. Guarner J, Bartlett J, Shieh WJ, Paddock CD, Visvesvara GS, Zaki SR. Histopathologic spectrum and immunohistochemical diagnosis of amebic meningoencephalitis. Mod Pathol. 2007. 20: 1230-7

9. Kim JH, Jung SY, Lee YJ, Song KJ, Kwon D, Kim K. Effect of therapeutic chemical agents in vitro and on experimental meningoencephalitis due to Naegleria fowleri. Antimicrob Agents Chemother. 2008. 52: 4010-6

10. Linam WM, Ahmed M, Cope JR, Chu C, Visvesvara GS, Da Silva AJ. Successful treatment of an adolescent with Naegleria fowleri primary amebic meningoencephalitis. Pediatrics. 2015. 135: e744-8

11. Martínez DY, Bravo-Cossio F, Valdivia-Tapia MD, Carreazo NY, Cabello-Vilchez AM. Successful treatment of primary amoebic meningoencephalitis using a novel therapeutic regimen including miltefosine and voriconazole. Acta Parasitologica. 2022. 67: 1421-4

12. Martínez DY, Seas C, Bravo F, Legua P, Ramos C, Cabello AM. Successful treatment of Balamuthia mandrillaris amoebic infection with extensive neurological and cutaneous involvement. Clin Infect Dis. 2010. 51: e7-11

13. Nicholls CL, Parsonson F, Gray LE, Heyer A, Donohue S, Wiseman G. Primary amoebic meningoencephalitis in North Queensland: The paediatric experience. Med J Aust. 2016. 205: 325-8

14. Ong TY, Khan NA, Siddiqui R. Brain-eating amoebae: Predilection sites in the brain and disease outcome. J Clin Microbiol. 2017. 55: 1989-97

15. Orozco L, Hanigan W, Khan M, Fratkin J, Lee M. Neurosurgical intervention in the diagnosis and treatment of Balamuthia mandrillaris encephalitis: Report of 3 cases. J Neurosurg. 2011. 115: 636-40

16. Schuster FL, Guglielmo BJ, Visvesvara GS. In-vitro activity of miltefosine and voriconazole on clinical isolates of free-living amebas: Balamuthia mandrillaris, Acanthamoeba spp. and Naegleria fowleri. J Eukaryot Microbiol. 2006. 53: 121-6

17. Seas RC, Bravo PF. Amebic granulomatosis encephalitis due to Balamuthia mandrillaris: A fatal disease increasingly recognized in Latin America. Rev Chilena Infectol. 2006. 23: 197-9

18. Singh P, Kochhar R, Vashishta RK, Khandelwal N, Prabhakar S, Mohindra S. Amebic meningoencephalitis: Spectrum of imaging findings. AJNR Am J Neuroradiol. 2006. 27: 1217-21

19. Tunkel AR, Glaser CA, Bloch KC, Sejvar JJ, Marra CM, Roos KL. The management of encephalitis: Clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2008. 47: 303-27

20. Visvesvara GS. Free-living amoebae as opportunistic agents of human disease. J Neuroparasitol. 2010. 1: 1-13

21. Visvesvara GS, Moura H, Schuster FL. Pathogenic and opportunistic free-living amoebae: Acanthamoeba spp. Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunol Med Microbiol. 2007. 50: N100802

22. Vollmer ME, Glaser C. A Balamuthia survivor. JMM Case Rep. 2016. 3: e005031

23. Zhang H, Cheng X. Various brain-eating amoebae: The Protozoa, the pathogenesis, and the disease. Front Med. 2021. 15: 842-66