Equine mares as reservoir hosts for pathogenic species of Leptospira

Identification of equine mares as reservoir hosts for pathogenic species of Leptospira
Front Vet Sci. 2024 May 9:11:1346713. doi: 10.3389/fvets.2024.1346713. eCollection 2024.
Authors
Camila Hamond 1 2 , Emma N Adam 3 , Nathan E Stone 4 , Karen LeCount 1 2 , Tammy Anderson 1 2 , Ellie J Putz 5 , Patrick Camp 1 , Jessica Hicks 1 , Tod Stuber 1 , Hans van der Linden 6 , Darrell O Bayles 5 , Jason W Sahl 4 , Linda K Schlater 1 2 , David M Wagner 4 , Jarlath E Nally 2 5
Affiliations

1 National Veterinary Services Laboratories, Animal and Plant Health Inspection Service, U.S. Department of Agriculture, Ames, IA, United States.
2 National Centers for Animal Health Leptospira Working Group, U.S. Department of Agriculture, Ames, IA, United States.
3 Department of Veterinary Science, University of Kentucky, Maxwell H. Gluck Equine Research Center, Lexington, KY, United States.
4 The Pathogen and Microbiome Institute, Northern Arizona University, Flagstaff, AZ, United States.
5 Infectious Bacterial Diseases Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Ames, IA, United States.
6 Department of Medical Microbiology and Infection Prevention, World Organisation for Animal Health (WOAH) and National Collaborating Centre for Reference and Research on Leptospirosis, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, Netherlands.

PMID: 38784659
PMCID: PMC11112012
DOI: 10.3389/fvets.2024.1346713

Abstract

Equine leptospirosis can result in abortion, stillbirth, neonatal death, placentitis, and uveitis. Horses can also act as subclinical reservoir hosts of infection, which are characterized as asymptomatic carriers that persistently excrete leptospires and transmit disease. In this study, PCR and culture were used to assess urinary shedding of pathogenic Leptospira from 37 asymptomatic mares. Three asymptomatic mares, designated as H2, H8, and H9, were PCR-positive for lipL32, a gene specific for pathogenic species of Leptospira. One asymptomatic mare, H9, was culture-positive, and the recovered isolate was classified as L. kirschneri serogroup Australis serovar Rushan. DNA capture and enrichment of Leptospira genomic DNA from PCR-positive, culture-negative samples determined that asymptomatic mare H8 was also shedding L. kirschneri serogroup Australis, whereas asymptomatic mare H2 was shedding L. interrogans serogroup Icterohaemorrhagiae. Sera from all asymptomatic mares were tested by the microscopic agglutination test (MAT) and 35 of 37 (94.6%) were seropositive with titers ranging from 1:100 to 1:3200. In contrast to asymptomatic mares, mare H44 presented with acute spontaneous abortion and a serum MAT titer of 1:102,400 to L. interrogans serogroup Pomona serovar Pomona. Comparison of L. kirschneri serogroup Australis strain H9 with that of L. interrogans serogroup Pomona strain H44 in the hamster model of leptospirosis corroborated differences in virulence of strains. Since lipopolysaccharide (LPS) is a protective antigen in bacterin vaccines, the LPS of strain H9 (associated with subclinical carriage) was compared with strain H44 (associated with spontaneous abortion). This revealed different LPS profiles and immunoreactivity with reference antisera. It is essential to know what species and serovars of Leptospira are circulating in equine populations to design efficacious vaccines and diagnostic tests. Our results demonstrate that horses in the US can act as reservoir hosts of leptospirosis and shed diverse pathogenic Leptospira species via urine. This report also details the detection of L. kirschneri serogroup Australis serovar Rushan, a species and serotype of Leptospira, not previously reported in the US.

Keywords: Australis; Leptospira; equine; kirschneri; leptospirosis.

Copyright © 2024 Hamond, Adam, Stone, LeCount, Anderson, Putz, Camp, Hicks, Stuber, van der Linden, Bayles, Sahl, Schlater, Wagner and Nally.