Free‐living amoebae: pathogenicity and immunity

Abstract

Free-living amoebae causes three well-defined disease entities: (i) primary amoebic meningoencephalitis, caused by Naegleria fowleri, (ii) granulomatous amoebic encephalitis and (iii) chronic amoebic keratitis, caused by species of Acanthamoeba. Both Naegleria infections and chronic amoebic keratitis occur in healthy individuals while granulomatous amoebic encephalitis is often associated with patients with acquired immunodeficiencies. The different pathogenic behaviour of these organisms is associated with differences in life cycle, amoeboidal locomotion, enzyme composition (such as phospholipase A), and cytotoxins, as well as natural host immunity. Immunity against these amoebae (whether acquired or natural) involves a combination of complement, antibody and cell-mediated immunity. Evidence suggests that the major mechanisms of immunity against these amoebae is activation of phagocytic cells, especially neutrophils, by lymphokines and opsonization of the amoebae by antibody which promote an antibody dependent cellular destruction of the organism.

Autoimmunity in the Mediation of Granulomatous Amoebic Encephalitis: Implications for Therapy

“…Conversely, amoebae can evade immune mechanisms by binding to a C1q component, as shown in the case of A. culbertsoni, and the parasite-derived serine proteases can degrade IgG and IgA , Kong, et al, 2000, Na, et al, 2002, Marciano-Cabral & Cabral, 2003. Neutrophils, macrophages, and microglia can destroy amoebae, and their amoebicidal effects are mediated in part by respiratory burst and nitric oxide under the influence of IL-1 , IL-1 , TNF-and/or IFN- (Ferrante, 1991a, Ferrante, 1991b, MarcianoCabral & Toney, 1998, Marciano-Cabral, et al, 2000, Benedetto & Auriault, 2002a, Benedetto & Auriault, 2002b, Dudley, et al, 2007, Khan, 2008. Affected patients, including healthy individuals upto 90%, carry the Acanthamoeba-reactive antibodies of IgM, IgG, and IgA isotypes with no significant differences between males (86.2%) and females (89.2%), indicating that humans are regularly exposed to Acanthamoeba and become sensitized with the amoebic antigens (Chappell, et al, 2001, McClellan, et al, 2002, Schuster, 2002, Khan, 2005a, Brindley, et al, 2009, da Rocha-Azevedo, et al, 2009.…”

Improvement of Antiamoebic Activity of Rokitamycin Loaded in Chitosan Microspheres

“…Since the early 1960s, Acanthamoeba has been recognized as an opportunistic human pathogen capable of causing infections in both immunocompetent and immunocompromised hosts [14,15]. In particular, Acanthamoeba spp.…”

Post-mortem culture of Balamuthia mandrillaris from the brain and cerebrospinal fluid of a case of granulomatous amoebic meningoencephalitis, using human brain microvascular endothelial cells

“…PAM, caused by Naegleria fowleri, is a fast progressing disease (lasting 7-14 days), affecting both immunocompromised and immunocompetent hosts. N. fowleri gains entry into the central nervous system (CNS) through the olfactory neuroepithelium, producing necrotizing and haemorrhagic meningoencephalitis, and is associated with stiff neck, headache, vomiting, fever and nausea (Barnett et al, 1996;Ferrante, 1991;Ma et al, 1990;Martinez & Visvesvara, 1997). In contrast, GAE can be caused by both Balamuthia mandrillaris and Acanthamoeba species and is thought to be initiated by the entry of amoebae through the lower respiratory tract or skin lesions, followed by haematogenous spread (reviewed by Khan, 2003;Marciano-Cabral & Cabral, 2003).…”