Opportunistic free-living amoebal pathogens

Abstract

Pathogenic free-living amoebae affecting the central nervous system are known to cause granulomatous amoebic encephalitis (GAE) or primary amoebic meningoencephalitis (PAM). Although hosts with impaired immunity are generally at a higher risk of severe disease, amoebae such as Naegleria fowleri and Balamuthia mandrillaris can instigate disease in otherwise immunocompetent individuals, whereas Acanthamoeba species mostly infect immunocompromised people. Acanthamoeba also cause a sight-threatening eye infection, mostly in contact lens wearers. Although infections due to pathogenic amoebae are considered rare, recently, these deadly amoebae were detected in water supplies in the USA. This is of particular concern, especially with global warming further exacerbating the problem. Herein, we describe the epidemiology, presentation, diagnosis, and management of free-living amoeba infections.

Keywords: Balamuthia; CNS infection; Free-living amoebae; Naegleria; acanthamoeba; encephalitis; keratitis; meningoencephalitis.

Figure 1.

A PhyML phylogenetic tree (GTR model) based on the 18S ribosomal gene of the three pathogens discussed in this study. Sequences obtained from genbank (https://www.ncbi.nlm.nih.gov/genbank/) were aligned using ClustalW version 2 [179] and the trees calculated using seaview version 4 [189]. The tree was rooted with Giardia intestinalis (AF473852.1) and Giardia ardeae (Z17210.1). Bootstrap analysis was performed using 1000 pseudo-replicates. The scale bar shows the evolutionary distance for the nucleotide substitutions per site.

Figure 2.

Diagnosis and management of brain-eating amoebae. Diagnostic tools and techniques used in the detection of A. castellanii, N. fowleri and B. mandrillaris are depicted. The compounds/drugs utilized in cases with successful outcomes and those tested in vitro against the three amoebae are also portrayed.