Seroprevalence, frequency of leptospiuria, and associated risk factors in horses in Kansas, Missouri, and Nebraska from 2016-2017

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.

Seroprevalence of Leptospira in Racehorses and Broodmares in New Zealand

“…As found in the current study, similar studies in Kansas [ 32 ] and Switzerland [ 33 ] reported high titres in the horses sampled that could be consistent with active infection, but no clinical signs of disease were reported in the horses. High antibody levels do not indicate if a horse is currently shedding Leptospira , as horses can be both seropositive or negative and be shedding the bacteria [ 8 , 32 ]. Although no inference about active infections in the cohort of horses reported in this study can be made, horses with active infections that are shedding may be a risk to both animals and people in contact with them [ 35 ].…”

“…A quarter of the horses in the cohort tested positive to at least one serovar, which is the same as the seroprevalence rates reported in Korea (25%) [ 28 ] and slightly lower than a study in Australia (29%) [ 29 ]. Studies in Brazil, Italy, and North America have reported higher rates of 45%, 67%, and 77% of horses testing positive to at least one serovar, respectively [ 30 , 31 , 32 ]. Direct comparisons of seroprevalence across geographic regions may be difficult due to variations in the positive titre cut-off used between studies and differences in endemic serovars across regions.…”

“…Flooding and increased rainfall have also been identified as risk factors for exposure to Leptospira in horses [ 32 , 44 ]. In contrast, the results of this study showed a reduced risk of exposure to any serovar with flooding.…”

Leptospira Seroprevalence in Bardigiano Horses in Northern Italy

“…Seroprevalences of 58.5% and 79% were found in Switzerland and in the Netherlands, respectively [14,15]. In a Brazilian study, the percentage of seropositivity was 71.4% [16] and a recent study carried out in some States of the American Midwest reported a 77% seroprevalence in healthy horses [17]. Surprisingly, a group of Italian researchers [10,11] reported a seroprevalence of 11.4% and 1.5%, respectively.…”

Seroprevalence of Leptospira spp. in Colorado equids and association with clinical disease

“…Serovar Bratislava is considered to be a host-adapted serovar for horses, which is reflected by high seroprevalence in the absence of clinical signs. 4,15,18,20 Serovars for which the horse is the incidental host generally cause more significant clinical disease. In horses, the serovars most commonly associated with severe morbidity are Pomona, notably Pomona strain Kennewicki, 7 and Grippotyphosa.…”