Nationwide seroepidemiology of canine exposure to Ehrlichia canis and Babesia spp. in Portugal (2015-2025): One Health biosentinel surveillance.

BACKGROUND

Ehrlichia canis and canine Babesia spp. are widely distributed tick-borne pathogens of veterinary and One Health relevance. Contemporary nationwide data on canine exposure and associated determinants in Portugal are limited. This study aimed to estimate seropositivity proportions and explore epidemiological determinants of exposure to E. canis and Babesia spp. in clinically suspected dogs from Portugal over an 11-year period (2015-2025).

METHODS

Serum samples from 2960 dogs collected between 2015 and 2025 were analysed using commercial enzyme-linked immunosorbent assay kits to detect immunoglobulin G antibodies to E. canis and Babesia spp. Associations with demographic and geographic variables were assessed using chi-square and Fisher's exact tests. Univariable and multivariable logistic regression were used to identify potential risk factors (P < 0.05), and model performance was evaluated using the Hosmer-Lemeshow test, Nagelkerke's R2, and the area under the receiver operating characteristic curve.

RESULTS

Overall seropositivity was 4.0% (116/2,872) for E. canis and 12.0% (337/2,818) for Babesia spp. Borderline results accounted for 3.0% (88/2,960) and 4.8% (142/2,960), respectively. E. canis seropositivity varied significantly by Nomenclature of Territorial Units for Statistics level 2 region (P < 0.001), with highest values in the Algarve (15.3%; odds ratio [OR] = 4.3, P < 0.001) and Setúbal Peninsula (50.0%; OR = 23.9, P = 0.025). Age was associated with E. canis exposure (P = 0.014), with increased odds in dogs aged 6 to < 11 years and ≥ 11 years (both OR = 2.1, P < 0.05). No significant geographical association was observed for Babesia spp. (P = 0.803), and sex and age were not significant predictors. Seropositivity to Babesia spp. was a risk factor for seropositivity to E. canis (OR = 3.6, P < 0.001). Multivariable models retained no independent predictors (Nagelkerke R2 = 0.15; area under the curve = 0.71).

CONCLUSIONS

This study provides a nationwide, long-term retrospective assessment of serological exposure to E. canis and Babesia spp. among clinically suspect dogs in Portugal. Exposure to E. canis showed marked regional heterogeneity, particularly in southern Portugal, whereas Babesia spp. showed no significant regional association. Co-seropositivity, although uncommon, is consistent with shared tick-borne exposure pathways. These findings support risk-based tick control and continued surveillance within a One Health framework.