Distribution and Current State of Molecular Genetic Characterization in Pathogenic Free-Living Amoebae

Free-living amoebae (FLA) are protozoa widely distributed in the environment, found in a great diversity of terrestrial biomes. However, few genera of FLA are linked to human infections. Within these genera, Acanthamoeba spp., classified by genotypes (T1-T23), being T1, T2, T4, T5, T10, T12, and T18 as capable of causing granulomatous amoebic encephalitis (GAE) in immunocompromised patients mostly and Acanthamoeba keratitis related to genotypes T2, T3, T4, T5, T6, T10, T11, T12 and T15 in apparently healthy patients. Meanwhile, Naegleria fowleri is the causative agent of an acute infection called primary amoebic meningoencephalitis (PAM), while Balamuthia mandrillaris, like some Acanthamoeba genotypes, causes GAE, differing from the latter in the description of numerous cases in patients immunocompetent. Finally, other FLA related to the pathologies mentioned above have been reported; Sappinia pedata is responsible for one case of amoebic encephalitis; Vermamoeba vermiformis has been found in cases of ocular damage, and its extraordinary capacity as endo-cytobiont for microorganisms of public health importance such as Legionella pneumophila, Bacillus anthracis, Pseudomonas aeruginosa, among others. In this review, issues related to the epidemiology of each one are addressed, updating their geographic distribution and cases reported in recent years for pathogenic FLA.