Environmental and management drivers of gastrointestinal nematodes in shelter dogs across mainland Portugal revealed by ecological niche modelling.

Gastrointestinal nematodes (GIN) are a major health concern in dogs, particularly in high-density environments such as shelters. Toxocara canis, Ancylostoma spp., and Trichuris vulpis are widely distributed, with recognised veterinary and zoonotic relevance. Effective prevention requires improved understanding of environmental and management-related risk factors driving transmission. This study investigated determinants of GIN infections in shelter dogs across Portugal. Faecal samples (n = 189), collected between November 2021 and October 2022 from 19 shelters, were analysed using coprological (mini-FLOTAC) and molecular (targeted PCR) methods. Infection risk was assessed using Boosted Regression Trees, Random Forest models, and ecological niche modelling (ENM), integrating climate, land use, shelter management, and host-related variables. Key risk factors included housing density (number of dogs per enclosure), age group, and deworming regimen, with parasite-specific patterns. Environmental predictors varied across species, with solar radiation, temperature, and soil characteristics influencing T. canis distribution, while land cover and precipitation were more relevant for T. vulpis and A. caninum. Marked spatial differences in the ecological suitability of the three GIN were evident. Spatial predictions indicated widespread risk of T. canis and T. vulpis across mainland Portugal, whereas higher-risk areas for A. caninum were concentrated in southern regions. Altogether, our findings highlight the combined influence of environmental conditions and shelter management on GIN transmission. The integration of eco-epidemiological and spatial modelling approaches using machine learning and ENM provide a useful framework for understanding local and regional nematode transmission dynamics and identifying high-risk settings, supporting targeted surveillance and more effective, shelter- and region-specific parasite control strategies.