Rishi Desai, MD, MPH

Naegleria fowleri (Primary amebic meningoencephalitis)

Wikipedia

First Aid 

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   