Bovine leptospirosis: Pathogenic species and serovars of Leptospira associated with dairy cows

Leptospirosis is an economically important zoonotic bacterial infection of livestock that causes abortions, stillbirths, infertility, and loss of milk production. Bovine leptospirosis occurs worldwide and is caused by infection with pathogenic bacteria in the genus Leptospira that can colonize the kidney or genital tract of both males and females to maintain disease transmission via shedding in urine, the reproductive tract, or via vertical transmission to a fetus. Cattle are a reservoir host for L. borgpetersenii serovar Hardjo but can also shed other pathogenic species and serovars associated with bovine infection and zoonotic transmission. In this observational study, urine samples (n = 384) were collected from dairy cows in a California slaughterhouse to test for the presence of pathogenic Leptospira. In total, 56 urine samples (15%) were positive, with 55 (14%) positive by lipL32 rtPCR and 24 (6%) positive by culture. Characterization of cultured isolates identified L. borgpetersenii serovar Hardjo (n = 18), L. interrogans serovar Pomona (n = 5), and L. interrogans serovar Copenhageni (n = 1). Leptospira targeted amplicon sequencing analysis of 32 lipL32 PCR-positive but culture-negative urine samples identified 23 as positive for L. borgpetersenii, one as positive for a mixed infection comprising L. borgpetersenii and L. santarosai, and 4 as positive for L. santarosai; 4 remained undefined. Phylogenetics identified a new genotype of L. borgpetersenii that was not readily amenable to culture using current medium formulations. The identification of species and serovars of Leptospira currently circulating in cattle is critical for efficacious surveillance, diagnostic, and prevention strategies.