Serogroup Distribution and High Seroprevalence of Bovine Leptospirosis in Southeastern Portalegre, Portugal

Abstract

Bovine leptospirosis is a globally distributed zoonotic disease with significant implications for animal health, public health, and livestock productivity. This study aimed to characterize the epidemiological status of leptospirosis in cattle from the Alto Alentejo region (Portugal), with particular emphasis on serogroup distribution and infection dynamics. Between February and June 2025, a total of 83 cattle from 11 farms were sampled across four municipalities. Serological analysis was performed using the microscopic agglutination test (MAT), while molecular detection of pathogenic Leptospira DNA was conducted using polymerase chain reaction (PCR) in selected calf samples. Overall, 81% of animals tested positive, suggesting widespread exposure and endemic circulation. The most prevalent serogroups were L. Pomona (27%), L. Mozdok (23%), and L. Pyrogenes (13%), accounting for over 78% of positive cases. Multiple serogroup reactivity was frequently observed, reflecting either repeated exposure or cross-reactivity. Infections were geographically widespread, with higher frequencies in extensive production systems. PCR confirmed active infection in calves, supporting the role of leptospirosis in acute disease and mortality events. Climatic conditions, particularly increased precipitation, likely contributed to environmental persistence and transmission. Overall, the findings suggest a complex epidemiological scenario involving multiple serogroups, environmental reservoirs, and host interactions in cattle from Alto Alentejo. However, the conclusions should be interpreted cautiously due to the relatively small sample size, limited geographic coverage, cross-sectional study design, and the restricted use of PCR analysis in selected samples. . These findings emphasize the need for improved surveillance, adapted vaccination strategies, and integrated control measures to mitigate the impact of bovine leptospirosis in southern Portugal.