Naegleria species (& their close relative Acanthamoeba) are pathogenic free-living amoebae, i.e. opportunistic rather than obligate pathogens, e.g. Naegleria fowleri. These organisms are ubiquitous in the environment, in soil, water and air. Infections in humans are rare but may be acquired through water entering the nasal passages (usually during swimming) and by inhalation.