Seropositivity and Antigen-Specific Seroreactivity to Leptospira spp. In Equids from Three Regions of Veracruz, Mexico

Information on Leptospira spp. exposure in Mexican equids remains limited. This cross-sectional study evaluated seropositivity and antigen-specific seroreactivity in 313 apparently healthy equids enrolled by convenience sampling in Los Tuxtlas (n = 119), Sotavento (n = 108), and Capital (n = 86), Veracruz, Mexico, from 2 October 2023 to 6 March 2024. Sera were examined by the microscopic agglutination test (MAT) against 13 antigens; titers ≥ 1:100 defined seropositivity. Overall seropositivity was 57.5% (180/313; 95% confidence interval [CI]: 52.0–62.9), with regional proportions of 49.6%, 65.7%, and 58.1%, respectively (unadjusted p = 0.048). Modified Poisson models with robust variance were fitted separately for region with species and region with sex. For Sotavento versus Los Tuxtlas, the adjusted prevalence ratio was 1.33 after adjustment for species (95% CI: 1.06–1.67) and 1.33 after adjustment for sex (95% CI: 1.06–1.66). Antigen-specific seroreactivity was most frequent for Australis (63/313; 20.1%), Bratislava (62/313; 19.8%), and Pyrogenes (57/313; 18.2%); these are overlapping antigen responses, not mutually exclusive serogroup estimates. Environmental and management exposures were not measured at the animal level. The findings support surveillance at the animal–human–environment interface but do not demonstrate active shedding or zoonotic transmission.