Letters to the Editor

GROWTH INHIBITION OF NÆGLERIA FOWLERI BY TETRACYCLINE, RIFAMYCIN, AND MICONAZOLE

Naegleria fowleri is a free-living amoeba that occurs ubiquitously in soil and water worldwide. As the infective form for humans, N. fowleri trophozoite enters the nasal cavity during recreational activities in contaminated water, crosses the olfactory neuroepithelium, travels through the olfactory nerves and the cribriform plate, and reaches the olfactory bulbs in the central nervous system, where it produces primary amoebic meningoencephalitis (PAM). Characterized by an extensive and robust inflammatory reaction, this acute and fatal disease is mainly attributed to the activities of neutrophils and some macrophages. In the absence of accurate diagnosis and specific treatment, this disease has a mortality rate of 95%–97% and a recovery rate of only 5%. Therefore elucidation of the pathogenic mechanisms and identification of the virulence factors of N. fowleri are critical for the development of novel therapeutic approaches for its ultimate control and eradication.

Primary amebic meningoencephalitis (PAM) is an emerging disease with a rapidly fatal outcome. Only eight reports of cured cases have appeared in the medical literature to date.

A 10-year-old boy developed PAM caused by Naegleria fowleri 1 week after swimming in an irrigation canal. He was admitted to our hospital after 9 h of severe headache and vomiting, fever, ataxic gait, mild confusion, and seizures were evident. Trophozoites were identified in the cerebrospinal fluid (CSF). Treatment with intravenous (i.v.) dexamethasone, amphotericin B, fluconaloze, and oral rifampicin was started. After several hours of conflicting clinical signs, recovery began, and on the third day he was conscious again. Hospital discharge occurred on day 23, after a normal brain CT scan. There was no sequel to the disease during the following 12 months.

The amebas present in the CSF were identified and confirmed as N. fowleri after observation of wet mounts and of cultures seeded on 1.5% non-nutrient agar plates covered with Escherichia coli, vegetative and cystic forms, enflagellation experiments in distilled water at 98°F, temperature tolerance testing and by indirect immunofluorescence using N. fowleri LEE antibody. The genotype was determined by PCR amplification and sequencing of the internal transcribed spacers (ITS) including the 5.8S rDNA.

Early treatment of PAM by i.v. administration of amphotericin B and fluconazole, and oral administration of rifampicin can offer some hope of cure for this devastating disease.

Primary amoebic meningoencephalitis due to Naegleria fowleri was found in a 38-year-old Chinese man living in Hong Kong who presumably acquired the infection from swimming in a hot spring in neighbouring China. Amoebic cysts were identified in tissue taken from a brain abscess. The patient responded to surgical drainage and a 6-week course of amphotericin B, rifampicin and chloramphenicol. This is one of 6 cases of successful treatment of primary amoebic meningoencephalitis documented in the medical literature.

During the past ten years it has become increasingly apparent that acanthamoebae can directly infect the cornea, usually after trauma, associated with contaminated water or soft contact lens wear. Thirteen cases of acanthamoebic keratitis have been published. In only three of these cases was the diagnosis first made by microbiologic methods, while in the others it was made only after pathologic examination of resected corneal specimens or enucleated eyes. We report three additional cases, two of which were accurately diagnosed by corneal scrape-smears and cultures before penetrating keratoplasty was performed. The reason for the accurate laboratory diagnosis in these cases was the presence of a diagnostic paracentral annular corneal infiltrate or abscess, a feature identified in over two-thirds of the earlier cases but one which has not been adequately emphasized or pursued for its early diagnostic value. We review the other clinical and epidemiological features of this entity, microbiological diagnostic techniques, the pathologic aspects, the role of topically and systemically administered medicaments, and finally point out the almost unavoidable role of penetrating keratoplasty after the temporizing effects of medical treatments have been achieved.

Primary amebic meningoencephalitis is a disease caused by the free-living amebae of the genera Naegleria or Acanthamoeba. The clinical course may result in death a few days after presentation or it may be insidious, with progressive neurologic deterioration and death after a chronic course. This article describes the organisms involved, the clinical course, pathology, diagnosis, and treatment of the disease.