1. INTRODUCTION
Free-living amoebae (FLA) are cosmopolitan and ubiquitous microorganisms
widely distributed in the environment and can be opportunistic and/or
pathogenic (Visvesvara et al., 2007). They have been isolated from many
natural and anthropogenic environmental matrices, including plants,
soil, air conditioning dust, bottled mineral water, drinking water
treatment and distribution system, and cooling towers (Landell et al.,
2013; Maschio et al., 2015; Javanmard et al., 2017; Soares et al., 2017;
Wopereis et al., 2020; Pazoki et al., 2020). They have also been
isolated from contact lenses, swimming pools, and other recreational
waters (Fabres et al., 2016; Santos et al., 2021; Fabros et al., 2021).
Among its representatives with importance for human health, the generaAcanthamoeba , Naegleria and Balamuthia stand out.Acanthamoeba spp. can cause illnesses in healthy people, such asAcanthamoeba keratitis (AK) which primarily affects contact lens
(CL) wearers, usually due to lens wear while swimming or improper lens
cleaning (Dos Santos et al., 2018). In immunosuppressed individuals, it
can cause Granulomatous Amebic Encephalitis (GAE), which can be fatal
(Visvesvara et al., 2007; Sarink et al., 2022). Acanthamoeba spp.
has also been reported to cause skin infections (Murakawa et al., 1995;
Paltiel et al. 2004). In addition, was isolated from 26% (17/63) of
critically ill patient urine samples (Santos et al., 2009); similarly,Acanthamoeba (T4) was isolated from 22% (11/50) of urine samples
collected from patients with recurrent urinary tract infection (Saberi
et al., 2021).
Naegleria fowleri is known as a “brain-eating amoeba”, and
primarily affects healthy young people using recreational waters,
causing primary amoebic meningoencephalitis (PAM) (Fowler and Carter,
1965). PAM is a serious and usually fatal disease if adequate treatment
is not initiated at the onset of symptoms (Król-Turmińska & Olender,
2017). The rapid deterioration in the health status of patient affected
by PAM, combined with the ease of being confused with bacterial
meningoencephalitis (since the symptoms are similar), as well as erratic
or late diagnosis, contribute to a high prevalence of deaths
(> 97%) (Capewell et al., 2010; Johnson et al., 2016).Balamuthia mandrillaris and Sappinia pedatta also
cause encephalitis (Gelman et al., 2001; Visvesvara et al., 2007; Cope
et al., 2019) however, there are no reports of the isolation of S.
diploidea pedatta from swimming pools and recreational waters.
The FLA essentially have two forms of life, namely, the trophozoite form
(with or without flagellum) which is the active form of the protozoan,
in which it feeds, reproduces and expresses pathogenicity; and the form
of cysts (which is the form of environmental resistance). Cysts have a
double-layer wall made essentially of cellulose (Garajová, et al., 2019)
that protects the protozoan against unfavorable conditions (e.g., food
shortages, dissection, extreme pH and temperatures) or antimicrobial
agents (e.g., NaCl, chlorine, drugs, UV, heat) (Aksozek et al., 2002;
Thomas et al., 2008; Chaúque and Rott, 2021; Chaúque et al., 2021). FLA
are considered the ”Trojan Horse” of the microbial world, as
phylogenetically diverse microorganisms including bacteria, fungi and
viruses survive and multiply within them; these microorganisms are
called amoeba-resistant microorganisms (ARM) (Greub & Raoult, 2004;
Scheid 2014 ; Delafont et al., 2016; Hubert et al., 2021; Rayamajhee et
al. 2021). A wide range of pathogens of public health importance have
been described as being ARM, including Legionella pneumophila,
Mycobacterium leprae, Pseudomonas spp., Candida auris and
various viruses (Maschio et al., 2015; Staggemeier et al., 2016; Balczun
& Scheid, 2017; Turankar et al., 2019; Nisar et al., 2020; Hubert et
al., 2021). All these aspects that characterize the profile of FLA
constitute the main attributes that determine the great importance of
these protozoa for human health and the environment.
Although increasingly prevalent, diseases caused by FLA remain rare;
however, the presence of these protozoa, especially in the aquatic
environment, is well documented (Stapleton, 2021; Saburi et al., 2017;
Caumo et al., 2009). The presence of FLA in swimming pools and other
recreational waters is of concern, as they can be pathogenic or
opportunistic and/or lead to the persistence of non-amoebic pathogens in
the water, including waters treated with chlorine-based disinfectants
(Siddiqui & Khan, 2014; Kiss et al., 2014; Dey et al., 2021). It was
determined that the prevalence of Naegleria spp in different
water sources around the world (considering data from 35 countries) was
26.42%, in recreational water it was 21.27% (10.80 - 34.11) and in
swimming pools was 44.80% (16.19 - 75.45 ) (Saberi et al., 2020),
however, the global prevalence of AFL in swimming pools and recreational
waters remains to be determined. The present systematic review and
meta-analysis aimed to determine the prevalence of FLA in swimming pools
and recreational waters worldwide.