Author ORCID Identifier

https://orcid.org/0000-0001-6458-7320

Year of Publication

2021

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department/School/Program

Veterinary Science

First Advisor

Dr. Craig N. Carter

Abstract

Leptospirosis is a reemerging zoonotic infection of worldwide importance and affects all mammals. The bacterium is transmitted to animals and humans by urine, fetal membranes and body fluids. Leptospira shedding in the urine contaminates both soil and water, exposing both humans and animals to the bacterium. Leptospirosis in horses can cause abortion and is one of the etiologies of equine recurrent uveitis which can lead to blindness. Equine leptospiral abortion in Central Kentucky is primarily caused by serovar Pomona, with occasional cases attributed to serovar Grippotyphosa. There are a few reports in the literature attributing abortion to serovar Bratislava in the United States. Interestingly, Bratislava has the highest seropositivity in the horse in the United States.

Two studies were conducted that are included in this dissertation. The first was to determine the prevalence of leptospirosis in horses located in Central Kentucky submitted for necropsy to the University of Kentucky Veterinary Diagnostic Laboratory. Heart, vitreous humor, kidney and urine samples were collected for microagglutination testing (MAT) and real-time PCR (qPCR). Heart blood and vitreous were tested using MAT for serovars Grippotyphosa, Pomona and Bratislava. Kidney, vitreous and urine samples were tested for pathogenic Leptospira by qPCR. MAT test results for heart blood indicated an increased seroprevalence for Bratislava as compared to Grippotyphosa and Pomona. Three horses had positive titers for serovar Bratislava in vitreous and heart blood samples. All urine samples tested negative by qPCR, and only one kidney sample had a weak positive result. Four vitreous samples tested positive for leptospirosis by qPCR, but all samples were negative upon MAT testing. No samples with positive MAT titers were positive by qPCR for any of the samples tested. Females were more likely to have positive MAT titers and were considerably older than males. MAT titers in females were also significantly higher as compared males. Finally, there was widespread seroprevalence in horses, regardless of the reason for necropsy submission. This suggests that exposure to Leptospira on Central Kentucky horse farms is common and the risk of exposure to humans and other animals is possible.

The second study evaluated the enzyme heme oxygenase-1 (HO-1) and its potential as a marker for abortion in pregnant mares with elevated MAT titers. HO-1 is the rate-limiting step in the breakdown and degradation of heme to carbon monoxide, free iron and biliverdin, which is converted to bilirubin. Increased levels of HO-1 and its’ by-products are upregulated during inflammation and sepsis. HO-1 together with its by-products are essential in protecting the body from both increased inflammation and in reducing the risk of sepsis in humans, mice and rats. HO-1 together with its by-products are also essential in helping maintain pregnancy in humans, mice and rats. HO-1 in the serum of horses has not been previously investigated. The presence of HO-1 in the serum of healthy non-pregnant mares (NPM), pregnant mares throughout pregnancy (PMOT), pregnant mares 7 months pregnant with and without placentitis (PM) and pregnant mares with high MAT titers (MATS) was investigated. HO-1 levels in both NPM and PMOT were lower than PM, and significantly lower than MATS. Pregnancy alone increased HO-1, the same has been shown in other mammals and humans. Additionally, mares pregnant with elevated leptospiral titers had significantly higher HO-1 levels compared to other mares. This indicates that both pregnancy and high MAT titers increase the animals’ HO-1 response. Further investigation of HO-1 in horses is needed to ascertain its’ importance during infection and/or pregnancy and potential therapeutics.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.371

Funding Information

This study was supported by the following grants:

Zoetis Animal Health-16EQRGBIO01 in 2015

Southeast Center for Agricultural Health and Injury Prevention, Via National Institute for Occupational Safety and Health/Center for Disease Control Cooperative Agreement (U50OH007547) in 2015

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