Predicting Naegleria fowleri freshwater habitat suitability in the United States for the present-day and future using ecological niche modeling.

Habitat suitability for the freshwater pathogen Naegleria fowleri, commonly known as the brain-eating amoebae, was assessed through ecological niche modeling. Using the machine learning algorithm Maxent and occurrence data from three datasets, present-day habitat suitability maps for the contiguous United States (US) were created, and the averaged models were used to project future habitat suitability for N. fowleri in 2021-2040 and 2041-2060 across three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5). The highest percent contributor for averaged present-day models was land cover followed by a different temperature-related variable for each dataset (mean diurnal range, isothermality, and mean temperature of the coldest quarter). Present-day maps of N. fowleri habitat suitability showed the highest values in the southern portion of the US, where hotspots of highly suitable habitat were observed, especially in states such as Florida and Texas. Large areas of highly unsuitable habitat were also noted within the US, suggesting that the distribution of N. fowleri is not uniform. Habitat suitability predictions also revealed that suitable habitat for N. fowleri varied significantly by watershed and state. Future habitat suitability was nuanced, with some areas experiencing increases and others decreases in habitat suitability. Although N. fowleri generally persist at elevated water temperatures and primary amoebic meningoencephalitis cases are predicted to increase in the future due to climate variability, future habitat suitability values decreased across many areas in the US for all three datasets, especially in areas that are considered current hotspots. Differences between future and present-day predictions showed that increases in habitat suitability for some geographic regions, especially in northern states, suggested a potential northward expansion of N. fowleri. Future research should experimentally test associations between environmental variables and the presence, survival, and proliferation of N. fowleri to further refine ecological niche models for these pathogenic amoebae.