Ecoepidemiological determinants of Borrelia infection in sigmodontine rodents from the Delta and Parana Islands ecoregion, Argentina.

We screened lung tissue from 770 sigmodontine rodents sampled in the Delta and Paraná Islands ecoregion for Borrelia spp. and obtained sequences clustered within the Borrelia burgdorferi sensu lato (s.l.) complex. Seventeen individuals were PCR-positive (prevalence 2.2%), distributed mainly in Akodon azarae (n = 11) and across five additional species. Using GLMMs that accounted for site and trapping session, infection probability was positively associated with individual body length and with ecological proxies of prior host and vector abundance: Ak. azarae abundance two sessions earlier (lag S-2) and Ixodes loricatus nymph abundance in the previous session (lag S-1) were the strongest predictors. These results point to transmission dynamics driven by recent host and immature-tick abundance rather than by climatic descriptors. Presence of cattle was associated with lower Borrelia prevalence in grazed grids (0.5% vs. 4.8% in Ak. azarae), and a univariable model restricted to Ak. azarae detected a significant negative association with cattle; however, this effect was not statistically significant in multivariable models that included host size and lagged abundance metrics. Our findings indicate localized endemic circulation of B. burgdorferi s.l. linked to host/vector demography, and highlight the need for integrated vector and reservoir monitoring to resolve mechanistic pathways and potential implications for animal and public health.