Naegleria fowleri (Primary amebic meningoencephalitis)

Summary of Naegleria fowleri (Primary amebic meningoencephalitis)

Naegleria fowleri is an amoeba that can be pathogenic, causing a fulminant brain infection known as primary amoebic meningoencephalitis. This microorganism is typically found in bodies of warm freshwater, such as ponds, lakes, rivers, and hot springs, and may gain access to the central nervous system through the cribriform plate. Amoebas can be seen on spinal fluid analysis. Amphotericin B, though not typically effective, is the treatment of choice.

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Naegleria fowleri (Primary amebic meningoencephalitis)

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Chapter 64 Central Nervous System Infections TREATMENT MEDICATIONS ▪ Current treatment regimes uncertain (based on in vitro studies, case reports) ▫ Antifungal, antiparasitic agents in combination ▫ Empiric antifungal regime: miltefosine, ﬂuconazole, pentamidine isethionate +/- trimethoprim-sulfamethoxazole, metronidazole, macrolide antibiotic SURGERY ▪ Single cerebral lesions ▫ Surgical resection NAEGLERIA FOWLERI (PRIMARY AMEBIC MENINGOENCEPHALITIS) osmosis.org/learn/naegleria_fowleri PATHOLOGY & CAUSES ▪ Thermophilic, free-living ameba, found in bodies of warm (stagnant), freshwater TYPES ▪ Life cycle, three forms 1. Cyst ▫ Immotile, dormant, survival phase ▫ Smooth, single-layered cell wall with single nucleus, naturally resistant to environmental factors ▫ Formation of cysts induced by unfavorable conditions such as food shortage, overcrowding, desiccation, accumulation of waste products, cold temperatures (< 10° celsius) 2. Trophozoite (ameboid) ▫ Feeding, reproductive, infective phase ▫ Transformation into trophozoites occurs around 25° celsius ▫ Reproduction occurs via binary ﬁssion (single cell divides into two offspring), optimal temperature 42° celsius 3. Biﬂagellate (two ﬂagella) ▫ Mobile, infective phase ▫ Pear-shaped body with two ﬂagella ▫ Flagellate phase occurs when ameba encounters change in ﬂuid ionic concentration → allows movement to suitable environment ▪ In human tissues Naegleria fowleri exists as ameboid trophozoite; ﬂagellate form may be found in CSF/during initial nasal insufﬂation Primary amoebic meningoencephalitis ▪ AKA naegleriasis ▪ Rare infection, fatality rate > 95% ▪ Mechanism of entry ▫ Insufﬂated into sinuses during waterbased activities → attaches to olfactory epithelium → follows olfactory axon through cribiform plate → migration to olfactory bulbs → spread throughout brain → diffuse meningoencephalitis ▪ In tissues, Naegleria fowleri feeds via two mechanisms; feeding on neurological tissue → necrosis, bleeding ▫ Phagocytosis of red, white blood cells ▫ Piecemeal consumption of astrocytes, neurons via amoebostome (actin-rich sucking apparatus extended from cell surface) OSMOSIS.ORG 355

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Naegleria fowleri (Primary amebic meningoencephalitis)

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A 30-year-old woman is brought to the emergency department by her partner due to high fever and severe headache accompanied by nausea and vomiting. The partner reported that the patient was fine until 2 days ago, when she started complaining of a headache and rapidly became confused. Temperature is 38.9°C (102°F), pulse is 80/min, respirations are 20/min, and blood pressure is 135/85 mmHg. On physical examination, the patient is obtunded and responds only to noxious stimuli. Pupils are equal and responsive to light. When the neck is flexed, the patient flexes the lower limbs. A thorough skin examination reveals no rashes, petechiae, or purpura. CSF analysis shows elevated WBC count with polymorphonuclear predominance, low glucose, high protein, and numerous RBCs. A wet mount is performed and reveals the following:

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Further review of this patient's history will most likely reveal which of the following?