Identification of equine mares as reservoir hosts for pathogenic species of .

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 from 37 asymptomatic mares. Three asymptomatic mares, designated as H2, H8, and H9, were PCR-positive for , a gene specific for pathogenic species of . One asymptomatic mare, H9, was culture-positive, and the recovered isolate was classified as serogroup Australis serovar Rushan. DNA capture and enrichment of genomic DNA from PCR-positive, culture-negative samples determined that asymptomatic mare H8 was also shedding serogroup Australis, whereas asymptomatic mare H2 was shedding 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 serogroup Pomona serovar Pomona. Comparison of serogroup Australis strain H9 with that of 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 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 species via urine. This report also details the detection of serogroup Australis serovar Rushan, a species and serotype of , not previously reported in the US.