Isolation and characterization of pathogenic leptospires associated with cattle

Authors: Nally, Jarlath; Hornsby, Richard; Alt, David; Bayles, Darrell; Wilson-Welder, Jennifer; Palmquist, Debra; BAUER, NATHAN - Food Safety Inspection Service (FSIS)

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2018
Publication Date: 3/19/2018
Citation: Nally, J.E., Hornsby, R.L., Alt, D.P., Bayles, D.O., Wilson-Welder, J.H., Bauer, N.E. 2018. Isolation and characterization of pathogenic leptospires associated with cattle. Veterinary Microbiology. 218:25-30. https://doi.org/10.1016/j.vetmic.2018.03.023.
DOI: https://doi.org/10.1016/j.vetmic.2018.03.023

Interpretive Summary: Pathogenic species of Leptospira cause leptospirosis, a global disease that is transmitted from animals to humans. Leptospires survive in the kidney of domestic and wild animal species, from where they are excreted via urine; contact with infected urine, or water contaminated with infected urine, can result in disease since pathogenic leptospires can penetrate breaches of the skin, or mucosal surfaces. Bovine leptospirosis is endemic in the United States and infection in cattle causes abortion, stillbirth, premature birth and reproductive failure. The disease is controlled using bacterin vaccines using isolates of leptospires cultured from cattle over 25 years ago. In this study, we applied a novel high throughput approach to culture new isolates of leptospires during visits to an abattoir facility. Our results indicate that 7.2% of cattle sampled were excreting leptospires. Twenty-three new isolates were obtained and these were all typed as L. borgpetersenii serovar Hardjo. These new isolates are being used to understand pathogenic mechanisms of persistent renal infection of cattle.

Technical Abstract: Pathogenic leptospires colonize the renal tubules of reservoir hosts of infection, including cattle, and are excreted via urine. In order to identify circulating serovars of pathogenic leptospires in beef cattle, and their associated rates of urinary excretion, a cross sectional study was performed. Fifty urine samples were collected one day each month over 12 consecutive months, directly from the bladder of beef cattle at a single slaughter facility and assessed for the presence of leptospires by culture and the fluorescent antibody test (FAT). Where possible, a matched serum sample was also collected for the microscopic agglutination test (MAT). Forty-three urine samples were either culture positive or FAT positive, indicating that 7.2% of sampled beef cattle were actively excreting leptospires in urine. Twenty-three urine samples were culture positive. Sequence analysis of 16S ribosomal DNA indicated that all isolates were Leptospira borgpetersenii. Typing by serology indicated that all isolates were serovar Hardjo. An overall seroprevalence of 20% (MAT = 1:25) was determined; positive bovine sera was most reactive to serogroup Sejroe (serovar Hardjo) (8.1%), and serogroup Australis (serovar Bratislava) (6.7%). There was poor correlation between seroprevalence and excretion of leptospires since 18/43 cattle, which were positive by culture or FAT, were seronegative. The virulence of two selected isolates of L. borgpetersenii serovar Hardjo was confirmed by experimental infection in small animal models of infection. Results confirm that serovar Hardjo continues to circulate in beef cattle and that multiple diagnostic assays are required to detect active shedding. These findings also highlight beef cattle as a reservoir host for the potential zoonotic transmission of leptospires.