Artificial Irrigation Impacts the Seasonal Occurrence of Pathogenic Leptospira in Its Wild Reservoirs in a Mediterranean Environment

BACKGROUND: Human activities play a significant role in the emergence of infectious diseases. We aimed to test whether artificial irrigation affects the occurrence of a zoonotic bacteria sensitive to desiccation, pathogenic Leptospira species (pathoLep), in micromammals inhabiting Mediterranean ecosystems. METHODS: A total of 361 individuals, including 217 Algerian mice (Mus spretus), 79 wood mice (Apodemus sylvaticus), and 65 greater white-toothed shrews (Crocidura russula), were captured during the four seasons of 2022 in six sites along a riparian forest close to a large city in north-eastern Spain and the surrounding agricultural fields, which are irrigated by flooding. A piece of kidney from each individual was analysed by means of two real-time PCR protocols targeting the lipL32 gene, which is exclusively found in pathoLep. Generalised Linear Models were used to study the factors that may be related to the presence of pathoLep. RESULTS: DNA of pathoLep was detected in 28% of the individuals, a relatively high occurrence compared to similar studies. The best model for the general micromammal population included four significant factors: season, age, species, and habitat. Prevalence was significantly lower during the dry seasons; in juveniles than in adult individuals; in the wood mouse than in the Algerian mouse and the shrew; and in natural than in agricultural habitats. Prevalence was consistently higher in agricultural habitats during all the seasons, reaching over 55% prevalence in these areas during spring. For the core species, the Algerian mouse, the best model included two factors (seasons and habitat), in the same sense as the general population model. CONCLUSIONS: This study shows that pathoLep are widespread among micromammals in the Middle Ebro Valley and that their occurrence is shaped by intrinsic and extrinsic factors. We identified a human activity (artificial irrigation) as an important driver favouring leptospiral survival in rural environments.