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An Overview of Parasite Diversity
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Discoba is an example of a group of organisms strongly supported and united by similar sequences in a number of genes but for which it is hard to define a unifying morphological trait. Nonetheless, included are some important parasite groups. One representative of note is Naegleria fowleri (Figure 2.9B) which typically dwells in warm, aerobic aquatic habitats, including some swimming pools. It can assume an amoeboid morphology, may transiently grow two flagella for swimming and dispersal and then disassemble them, or it can round up and encyst. It is worth mentioning here because occasionally people swimming in a habitat occupied by N. fowleri snuff this organism deep into their nasal chambers. If so, it can move through the small passages in the cribiform plate that separates the nasal chamber from the brain. It then begins to phagocytose cells of the brain, an ailment called primary amebic meningoencephalitis, or PAM. N. fowleri is frequently characterized as an opportunistic parasite though human infections for the otherwise free-living organism are a dead end. Infections, though rare, are almost always fatal for the affected person.
Central Nervous System Infections
Published in Miriam Orcutt, Clare Shortall, Sarah Walpole, Aula Abbara, Sylvia Garry, Rita Issa, Alimuddin Zumla, Ibrahim Abubakar, Handbook of Refugee Health, 2021
Meningoencephalitis is defined as inflammation of both the meninges and the brain. Most organisms that can cause meningitis or encephalitis can cause meningoencephalitis. Rarer aetiologies to consider include primary amoebic meningoencephalitis, which is associated with swimming in warm fresh water, and Naegleria fowleri, which is transmitted intranasally, leading to CNS invasion. Meningoencephalitis presents with fever, meningism and convulsions.
Liposomal Amphotericin B
Published in M. Lindsay Grayson, Sara E. Cosgrove, Suzanne M. Crowe, M. Lindsay Grayson, William Hope, James S. McCarthy, John Mills, Johan W. Mouton, David L. Paterson, Kucers’ The Use of Antibiotics, 2017
Nenad Macesic, Neil R. H. Stone, John R. Wingard
Naegleria fowleri is a free-living amoeba that can cause primary amoebic meningoencephalitis (PAM), an extremely rare yet almost universally fatal infection of the CNS. DAmB has been part of treatment regimens in the few cases of survival (Vargas-Zepeda et al., 2005). A mouse model found LAmB to be less effective than DAmB in vitro (Goswick and Brenner, 2003); therefore liposomal formulations of AmB are generally avoided in the treatment of PAM.
Epidemiology of free-living amoebae in the Philippines: a review and update
Published in Pathogens and Global Health, 2022
Giovanni D. Milanez, Frederick R. Masangkay, Gregorio L. Martin I, Ma. Frieda Z Hapan, Edilberto P. Manahan, Jeffrey Castillo, Panagiotis Karanis
Among the FLAs, the genera belonging to Naegleria, Acanthamoeba, Balamuthia, and Sappinia are considered by the World Health Organization (WHO) as medically important due to the morbidity or mortality reports in humans [16]. The route of cerebral infections for pathogenic FLA, in particular Naegleria spp., is initiated by the entry of the amoeba via the nasal cavity usually upon inhalation of contaminated water [17]. Upon reaching the brain via the cribriform plate, FLAs can mediate cytopathic effects resulting in the inflammation of the brain known as meningitis [18]. Depending on the FLA species or genotype and type of infection, conditions have been referred to as Primary Amoebic Meningoencephalitis (PAM) for Naegleria spp. infections [19], Granulomatous Amoebic Meningoencephalitis (GAE) for Acanthamoeba spp. infection [20], Balamuthia Amoebic Encephalitis (BAE) for Balamuthia mandrillaris infection, and Sappinia Amoebic Encephalitis (SAE) for Sappinia spp. infections [21]. Clinical conditions have almost equal morbidity to mortality ratio due to the rapid progression of the disease following the onset of symptoms [22]. Further, the symptoms presented by FLA-related meningitis mimic viral and bacterial forms, thus, making diagnosis and management of the disease challenging for clinicians and almost always leads to death [23]. Among the FLAs, pathogenic genotypes of Acanthamoeba spp. can inflict extra-cerebral infections like Acanthamoeba keratitis, and in rare cases, disseminated cutaneous infection [24–27].
Opportunistic free-living amoebal pathogens
Published in Pathogens and Global Health, 2022
Mohammad Ridwane Mungroo, Naveed Ahmed Khan, Sutherland Maciver, Ruqaiyyah Siddiqui
Acanthamoeba spp. infect the CNS, causing granulomatous amoebic encephalitis (GAE), and can also cause a sight-threatening eye infection known as Acanthamoeba keratitis (AK) [10, 11, 12]. B. mandrillaris is known to instigate Balamuthia amoebic encephalitis (BAE) in the CNS and infect other organs such as the lungs and skin, in both immunocompetent and immunocompromised individuals [11]. N. fowleri infects the CNS, causing primary amoebic meningoencephalitis (PAM), triggering a prompt onset of disease and leading to death within days [11, 13]. Treatment of CNS infection with amoebae is complicated and hampered by the selectivity of the blood-brain barrier (BBB) that affects drug permeability into the brain. The purpose of this review is to briefly describe the epidemiology, presentation, diagnosis and management of CNS complications due to free-living amoeba and keratitis caused by pathogenic Acanthamoeba.
Drug discovery for primary amebic meningoencephalitis: from screen to identification of leads
Published in Expert Review of Anti-infective Therapy, 2021
Naegleria spp. are free-living amebae that belong to the family Vahlkampfiidae and class Heterolobosea. Although these amebae are around for more than 100 years, a thermophilic ameboflagellate N. fowleri has attracted much attention because it causes a rapidly progressive and often fatal meningoencephalitis known as primary amebic meningoencephalitis (PAM). The infective form of N. fowleri is the trophozoite state, which is able to infect human by entering through the nasal cavity during swimming or other recreational water activities, and nasal cleansing. The trophozoite then attaches to the nasal mucosa, penetrates the olfactory neuroepithelium, migrates through the olfactory nerve, crosses the cribriform plate and reaches the olfactory bulb [1,2]. Once N. fowleri trophozoites reach brain parenchyma, they induce extensive inflammation, leading to the destruction of host nerves and the subsequent tissue damage in the central nervous system (CNS) [3]. The clinical symptoms can be divided into stage 1 and stage 2. Symptoms in stage 1 include severe frontal headache, nausea, vomiting, and a fever. Progression of these initial symptoms leads to a more severe stage 2 that includes stiff neck, altered mental status, seizures, cerebral edema, cerebellar herniation, and finally coma leading to death in approximately one week after the onset of symptoms [4]. These symptoms resemble the signs of bacterial or viral meningitis and delay the timely diagnosis of PAM.