Free-living amoebae (FLA) are protozoa widely distributed and have been isolated from the most diverse environments, such as tap water, swimming pools, cooling towers, air conditioners, dust, contact lenses and storage cases, among others. The genera Naegleria, Acanthamoeba, Balamuthia and Sappinia are part of this group (Khan, 2006). They are considered amphizoic and can become pathogenic if given the opportunistic (Trabelsi et al., 2012). They have two forms of life, the trophozoite through which they move, feed and reproduce and the cyst that is the form of resistance, protecting them from unfavorable conditions for their survival such as changes in temperature, pH and salinity (Khan, 2006; Schuster et al., 2004). One of the genera that have drawn attention for being more vulnerable to climate change and for being highly lethal is Naegleria (De Jonckheere, 2012).

This genus comprises several non-pathogenic species such as Naegleria australiensis and Naegleria italica (Visvesvara et al., 2007). In contrast the highly pathogenic Naegleria fowleri in most cases it leads to death. It is known popularly as the “brain-eating amoeba'' which has afflicted humans and animals (Mungroo et al., 2019). It is a thermophilic microorganism, supporting temperatures above 45 °C (Visvesvara et al., 2007). According to De Jonckheere (2011) N. fowleri is present on all continents except Antarctica. It is mainly found in lakes, ponds, and groundwater but not in sea water. The movement of the sediment at the bottom of these waters through boisterous play, causes the motile flagellated forms and trophozoites to enter the nose of individuals (mostly young males). When these encounter the nasal passages, they travel a path that will take them to the human olfactory epithelium and pass the cribriform plate to the brain through the olfactory cell axon (Baig et al., 2014; Visvesvara, 2013). N. fowleri settles in the meninges causing Primary Amoebic Meningoencephalitis (PAM), whose symptoms are similar to those of bacterial or viral meningitis: severe frontal headache, fever, neck stiffness, vomiting, mental confusion, hallucinations and cerebral hemorrhages. The course of this infection is approximately 7 days with a fatal outcome in the overwhelming majority of cases (Siddiqui and Khan, 2014; Heggie, 2010). In the USA alone, according to Centers for Disease Control (CDC), 151 cases of PAM were recorded in the period between 1962 and 2020, with only 5 survivors (CDC, 2021a). More cases have emerged around the world lately, not only through swimming, but also due to the use of neti pot or ablution rituals (Ghanchi et al., 2016). In recent years, cases among animals have also been reported more frequently. So far, there is no effective treatment against this disease (Mahmood, 2015; Siddiqui and Khan, 2014).

In the context, it is understood the need for a One Health approach linking the health of humans, animals, plants and the environment (McEwen and Collignon, 2018). Zinsstag et al. (2021) defined One Health as any added value for saving both human and animal lives, reducing costs and providing sustainable social and environmental services with interdisciplinary cooperation in favor of human and animal health. The four international agencies: the Food and Agriculture Organization of the United Nations (FAO), the World Organisation for Animal Health (OIE), the UN Environment Programme (UNEP) and the World Health Organization (WHO), have signed a agreement (Quadripartite MoU) to integrate human, animal, plant and ecosystem areas, reinforcing national and regional health systems and services (WHO, 2022). Depending on view and approaches, the One Health concept may be related with “One Medicine, One Medicine-One Health, One World-One Health, EcoHealth, and Planetary Health” (Pettan-Brewer et al., 2021). Several factors can influence the environment, causing instability. According to Ellwanger et al. (2020) global warming has consequences for the spread of infections, due to anthropogenic actions (emission of greenhouse gases from industries and extensive use of fossil fuels). The indiscriminate use of antimicrobials in human and animal health, pesticides and wildlife trade can lead to the transmission of pathogens that are often lethal (Hernando-Amado et al., 2019; Essack, 2018; Cunningham et al., 2017). Within this context there are microorganisms that have an ecological role in nature, but that, due to changes in the environment, can become pathogenic, such as free-living amoebae (FLA) (Samba-Louaka et al., 2019). According to Angelici et al. (2021), there is a need for a multidisciplinary and transdisciplinary integrated health approaches to understand and mitigate infectious diseases caused by neglected protist pathogens, which is in line with the One Health vision. In this review, we take a One Health approaches on occurrence of N. fowleri and their implications on human, animal, plant and environmental health.