Abstract
Leptospirosis is a worldwide veterinary and public health concern, and well recognized infectious disease of horses. Seroprevalence rates vary with geography, but many studies have confirmed a high exposure rate. The correlation between seropositivity and shedding status has not been made in horses, however. The aims of this study were to use semi-nested PCR on urine from apparently healthy horses to determine period prevalence of leptospiral shedding and to correlate these findings with MAT results to establish associations with client based survey data regarding horse management and environment. Serum and free-catch urine were collected from 204 healthy horses between May 2016-December 2017. Serum was used to determine GGT, creatinine concentrations, and six serovar MAT. Urine samples were submitted for PCR testing of leptospiral 23S rRNA. Client consent and survey data were collected for all subjects. Potential risk factors included drinking water source, exposure to livestock and dogs, geographical location, season, and precipitation. Two horses were positive on urine PCR for leptospirosis (shedding prevalence 1%), yet only one had a high reciprocal MAT titer of ≥ 800. Both horses were negative on urine PCR one month later without treatment. Approximately 77% of horses (157/204) were seroreactive (MAT reciprocal titer ≥ 100) with titers to serogroup Australis detected more frequently than others (47.5%; (97/204)). Apparently healthy horses infrequently shed Leptospira spp. in urine, yet seroreactivity in clinically normal horses is high (77%), confirming high exposure rates to Leptospira spp. in the Central Midwest.
Highlights
Leptospirosis, one of the most important worldwide zoonotic diseases, can present in horses in a number of ways
Our hypotheses were that seroprevalence would be high in the study population, urinary shedding of pathogenic leptospires would be lower than seroprevalence and not predicted by serological titers, and that horses stabled outside, living near fresh water sources such as ponds, and living in close proximity to dogs and/or livestock would be at greater risk for seropositivity and urinary shedding of pathogenic leptospires
Serum samples were submitted for measurement of creatinine and gamma glutamyl transferase (GGT), and performance of the microscopic agglutination test (MAT), while the urine sample was submitted for identification of pathogenic leptospires by polymerase chain reaction (PCR)
Summary
Leptospirosis, one of the most important worldwide zoonotic diseases, can present in horses in a number of ways. As many clinical signs associated with leptospirosis are non-specific, disease in horses may occur more frequently than is diagnosed, and exposure to Leptospira spp. may be more prevalent than was previously thought. Epidemiological studies typically employ the microscopic agglutination test (MAT) to determine a seroprevalence rate In these serological survey studies, the MAT provides information on exposure rates and suspected infecting serogroups in the geographic region being studied, but tells nothing about the carrier or shedding status of the horses. An investigation of urine shedding of Leptospira spp. by asymptomatic horses in the Central Midwest using PCR has not been performed This information would be of practical use for determining carrier prevalence in a specific geographical area, as well as increasing awareness of the potential for infectious and zoonotic spread by horses in the environment and to their owners
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