Exploring the impacts of El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) on the spatial distribution of Fasciola spp. in the Gilan province, Iran.

This study investigated the correlation between large-scale climate phenomena, particularly El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), and the distribution of Fasciola species in Gilan province, Iran. Climate change significantly impacts animal health, particularly through vector-borne diseases. Fasciola spp. is highly sensitive to temperature and soil moisture conditions, making its relationship with climate complex and influenced by various meteorological variables. ENSO and NAO index data were obtained from National Oceanic and Atmospheric Administration (NOAA). Local meteorological data from 4 Gilan stations and Fasciola spp. distribution data were collected for 20-year period. Correlation analysis between climate factors and Fasciola spp. distribution was performed, considering time lags at 95 % confidence level. Results showed a significant relationship (P-value <0.05) between monthly precipitation, ENSO indices (Southern Oscillation Index, Oceanic Niño Index, Multivariate ENSO Index), and the NAO index with varying time lags. Fasciola spp. distribution in livestock demonstrated significant correlations with the SOI index (negative correlation) and the ONI index (positive correlation), as well as strong negative correlations with average monthly temperature, soil temperature, and wet temperature. In conclusion, the distribution of Fasciola spp. based on the ONI index, was generally higher in years with El Niño events than in years with La Niña events. El Niño's increased rainfall creates ideal conditions for intermediate host snails, facilitating Fasciola spp. transmission. Conversely, La Niña's drier conditions restrict intermediate host survival, decreasing Fasciola spp. distribution. These findings enhance understanding of Fasciola spp. transmission dynamics in Gilan, aiding development of climate-responsive control strategies.