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Coxiella burnetii seropositivity and associated risk factors in sheep, goats, their farm workers and veterinarians in Ontario, Canada

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Title: Coxiella burnetii seropositivity and associated risk factors in sheep, goats, their farm workers and veterinarians in Ontario, Canada
Author: Meadows, Shannon
Department: Department of Population Medicine
Program: Population Medicine
Advisor: Menzies, PaulaJones-Bitton, Andria
Abstract: This thesis was conducted to investigate the seroprevalence and risk factors for Coxiella burnetii exposure in meat and dairy sheep and goats, their farm workers, and small ruminant veterinarians and veterinary students in Ontario. Four cross-sectional studies involving serological testing and questionnaire administration were conducted. Sera from reproductively active ewes and does were tested for C. burnetii specific antibodies using an Enzyme-Linked Immunosorbent Assay (IDEXX); human sera were tested using an Immuno-Fluorescence Assay (Focus Diagnostics). Seropositivity was common among all groups. The individual-level seroprevalence was 14.7% (95% CI=13.3-16.2) in sheep, 32.5% (95%CI=30.6-34.5) in goats, 64.5% (95%CI=57.2-71.4) in farm workers, and 59.4% (95%CI=41.9-75.2) in veterinarians/veterinary students. Overall, 48.6% (95%CI=37.2-60.1) of sheep farms and 63.2% (95%CI=51.9-73.4) of goat farms had at least one seropositive animal, while 76.3% (95%CI=65.8-84.6) of farms that participated in human testing had at least one seropositive farm worker. Mixed logistic multivariable models of individual seropositivity, and controlling for clustering by farm, were constructed for sheep, goats and farm workers. The sheep and goat models highlighted the importance of farm hygiene and biosecurity measures. Female flock size (log10 scale), lambing/kidding in a separate airspace, and failure to disinfect lambing/kidding pens were positively associated with seropositivity in both the sheep and goat models. For goats, male herd size (log10 scale), and kidding outdoors in the absence of swine on farm were negatively associated with seropositivity; the presence of other sheep/goat farms within 5km was positively associated with seropositivity. For sheep, loaning sheep was positively associated with seropositivity. Workers on dairy goat farms had higher odds of seropositivity, compared to working on meat goat or dairy sheep farms. Increasing proportions of seropositive sheep/goats on farm was also positively associated with farm worker seropositivity. Veterinary students had significantly lower odds of seropositivity than practicing veterinarians in univariable exact logistic regression.
Date: 2014-05
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