Animal leptospirosis, exempt in rodents, manifests as peculiar biology where the animal can function, simultaneously or not, as a susceptible host or reservoir. In the first case, clinical symptoms are likely. In the second case, infection is subclinical and manifestations are mild or absent. Mild clinical symptoms encompass reproductive failure in production animals for host-adapted Leptospira sp. serovars. This work presents a study on Leptospira sp. infection in a mixed-species (bovine and swine) farm with documented reproductive disorders in the cattle unit. A long calving interval (above 450 days) was the hallmark observed in cows. Some cows (2/26 tested) presented a high titre of antibodies against Leptospira sp. serogroup Sejroe, but the overall within-herd prevalence was low (11.5% and 7.7% for cut-off titres of 1:30 and 1:100, respectively). The in-herd prevalence of leptospirosis in the sow unit (determined for 113/140 animals) was high when using a lowered cut-off threshold (32.7% vs. 1.8% for cut-off titre of 1:30 and 1:100, respectively). In this unit, the most prevalent serogroup was Autumnalis. The final diagnostic confirmation of Leptospira sp. maintenance within the farm was obtained through detection by PCR of Leptospira sp. DNA in an aborted swine litter. Despite the fact that a common causative infective agent was diagnosed in both species, the direct link between the two animal units was not found. Factors such as drinking from the same water source and the use of manure prepared with the swine slurry might raise suspicion of a possible cross-contamination between the two units. In conclusion, this work suggests that leptospirosis be included in the differential diagnosis of reproductive disorders and spontaneous abortions in production animals and provides data that justify the use of a lowered threshold cut-off for herd diagnosis.
Keywords: PCR; diagnosis of leptospirosis; diagnostic cut-off; reproductive problems; spontaneous abortion.