Seroprevalence, frequency of leptospiuria, and associated risk factors in horses in Kansas, Missouri, and Nebraska from 2016-2017.
Authors: Trimble Amanda C, Blevins Christopher A, Beard Laurie A, Deforno Ashley R, Davis Elizabeth G
Journal: PloS one
Summary
# Editorial Summary: Leptospirosis in Central Midwest Horses Leptospirosis poses significant occupational risks to equine professionals, yet the relationship between serological evidence of exposure and actual bacterial shedding remains poorly understood in horses. Researchers collected serum and urine samples from 204 clinically healthy horses across Kansas, Missouri, and Nebraska between May 2016 and December 2017, testing for leptospiral antibodies via microscopic agglutination testing (MAT) and shedding via PCR of urinary leptospiral 23S rRNA, whilst correlating findings with management practices and environmental factors. Whilst 77% of horses (157/204) demonstrated seroreactivity at MAT titres ≥1:100—with serogroup Australis most prevalent at 47.5%—active urinary shedding was remarkably rare at just 1% (2/204), and notably, neither horse required treatment to clear infection within a month. These findings suggest that seropositivity substantially overestimates infection risk in apparently healthy horses, which has important implications for biosecurity protocols and zoonotic transmission concerns amongst farriers, veterinarians, and handlers who may otherwise assume seropositive horses represent an ongoing infectious threat. The high exposure rates documented across this region warrant continued vigilance around occupational exposure prevention, particularly given the public health implications, but practitioners should recognise that routine screening of clinically normal horses may generate false alarm regarding active shedding status.
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Practical Takeaways
- •High seroprevalence (77%) indicates most horses in this region have been exposed to Leptospira, but active shedding is uncommon—focus on biosecurity and environmental management rather than treating all exposed horses
- •A positive serology result does not indicate current infection or shedding status; urine PCR may be needed if active leptospirosis is suspected in a clinical case
- •Consider Leptospira spp. exposure as a potential risk factor when managing herds in the Central Midwest, particularly regarding water sources and contact with other species
Key Findings
- •77% of apparently healthy horses (157/204) were seroreactive to Leptospira spp., indicating high exposure rates in the Central Midwest
- •Serogroup Australis was the most frequently detected serovar at 47.5% (97/204) of the population
- •Only 1% of horses (2/204) shed leptospiral DNA in urine despite high seroprevalence, suggesting active shedding is rare in healthy horses
- •Seroreactivity did not correlate with active shedding status, as only 1 of 2 PCR-positive horses had high MAT titers ≥800