Authors: Hamond Camila, Adam Emma N, Stone Nathan E, LeCount Karen, Anderson Tammy, Putz Ellie J, Camp Patrick, Hicks Jessica, Stuber Tod, van der Linden Hans, Bayles Darrell O, Sahl Jason W, Schlater Linda K, Wagner David M, Nally Jarlath E
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Equine leptospirosis poses significant reproductive and ocular threats, yet the disease's epidemiology in asymptomatic carrier horses remains poorly characterised in the United States. Researchers used PCR, bacterial culture, and genomic sequencing to screen urine samples from 37 clinically normal mares, alongside serological testing via microscopic agglutination test (MAT) and comparative virulence assessment using a hamster infection model. Three mares shed pathogenic Leptospira DNA, with one culture-positive isolate confirmed as *L. kirschneri* serogroup Australis serovar Rushan—the first documented case of this strain in the US—whilst DNA analysis revealed a second mare was shedding *L. kirschneri* Australis and a third was shedding *L. interrogans* serogroup Icterohaemorrhagiae; notably, 94.6% of the asymptomatic cohort were seropositive with MAT titres ranging from 1:100 to 1:3200. Strain comparison revealed distinct lipopolysaccharide profiles and virulence differences between the subclinical and abortion-associated isolates, indicating that vaccine efficacy depends on matching circulating strains. These findings underscore that UK and international equine populations likely harbour multiple pathogenic Leptospira species via unapparent shedders, necessitating updated vaccine formulations, enhanced diagnostic protocols that cover emerging serovars, and epidemiological surveillance of breeding stock to mitigate reproductive losses and transmission risk.
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Practical Takeaways
- •Horses in the US act as asymptomatic reservoir hosts and can persistently shed multiple pathogenic Leptospira species in urine, posing transmission risk to other animals and potentially humans
- •High seroprevalence (94.6%) indicates widespread exposure in equine populations; current vaccines may not protect against all circulating species/serovars, particularly L. kirschneri Australis
- •Serological testing alone cannot identify active shedders—PCR and culture are needed to identify subclinical carriers; consider urinary shedding risk when managing mares with reproductive failure and high MAT titers
Key Findings
- •3 of 37 asymptomatic mares (8.1%) were PCR-positive for pathogenic Leptospira lipL32 gene; 1 mare was culture-positive
- •94.6% of asymptomatic mares (35/37) were seropositive for Leptospira by MAT with titers ranging from 1:100 to 1:3200
- •Two distinct pathogenic species identified: L. kirschneri serogroup Australis and L. interrogans serogroup Icterohaemorrhagiae in asymptomatic carriers; L. interrogans serogroup Pomona in aborting mare
- •L. kirschneri serogroup Australis serovar Rushan detected in US horses for the first time; different LPS profiles between subclinical carrier and aborting strains suggest differential virulence