Assay Development and Characterization of Mycoplasma Ovis

Kathy Ann Johnson, Purdue University

Abstract

The hemotrophic mycoplasma, Mycoplasma ovis, is found in sheep and goats throughout the world. This pathogenic bacterium is capable of causing an acute, life-threatening infection as well as chronic or subclinical infections in these animals. The purposes of the present studies were to develop M. ovis-specific assays for detection of this hemoplasma, and to better understand infection dynamics within pregnant ewes and lambs. The first study describes the development and validation of a SYBR® Green quantitative PCR (qPCR) assay, which was subsequently used to determine the prevalence of M. ovis infection within a population of goats and to evaluate risk factors for infection. This highly sensitive and specific assay consistently detected as few as 10 copies of plasmid/reaction. Convenience-based sampling of 362 goats from 61 farms located in Indiana revealed a prevalence of infection of 18% (95% confidence interval (CI), 14% to 22%). Bacterial loads of M. ovis ranged from 1.05 x 103 to 1.85 x 105 copies/mL of blood with a mean of 1.31 x 104 copies/mL of blood. The only risk factor associated with hemoplasma infection was the production use of the goat; dairy goats had a 3.3 fold increase compared with the prevalence in goats used for meat. This study not only demonstrates that M. ovis infection is common in goats in Indiana, but shows the variability of bacterial loads that can be found in chronically-infected animals. While sub-clinically infected goats may have a bacteremia, levels are characteristically less than 2.0 x 105 copies/mL. The second project utilized a combination of cross-sectional and longitudinal studies to estimate the prevalence of M. ovis infection from a cohort of naturally-infected pregnant ewes, assess changes in their bacterial loads, and determine the incidence of M. ovis in lambs pre- and post-weaning. The prevalence of M. ovis infection in ewes was not found to be significantly different during pregnancy, and before and after weaning of the lambs, with prevalence estimates of 45% (95% CI, 23.1 – 68.5), 36% (95% CI, 17.9 – 57.4), and 44%, (95% CI, 24.4 – 65.1), respectively. Bacterial loads of the ewes from the cross-sectional study ranged from 104 to 109 copies/mL of blood, with the median bacterial load at 105 copies/mL of blood. While higher bacterial loads are typical of an acute infection, none of the ewes in this study had overt clinical signs. The data suggest that M. ovis loads may be higher in pregnant sheep, particularly in ewes half-way through pregnancy. Most of the M. ovis infections in the study lambs were detected postweaning which suggests that transplacental or transmammary infection of M. ovis are unlikely routes. In the third study, a subset of M. ovis genes for use in a multi-locus sequence typing assay (MLST) were evaluated.

Degree

Ph.D.

Advisors

Camp, Purdue University.

Subject Area

Entomology|Epidemiology|Genetics|Immunology|Systematic biology

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