Browsing by Author "Kastelic, John Patrick"

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    Antimicrobial Stewardship: A One Health approach with a focus on antimicrobial reduction in dairy cattle
    (2023-05-01) McCubbin, Kayley Dawn; Barkema, Herman W.; Orsel, Karin; Sanchez, Javier; Kelton, David Francis; Kastelic, John Patrick
    Antimicrobial resistance (AMR) is considered one of the greatest threats facing humanity. Without intervention, AMR impacts are expected to be substantial, compromising human, animal, environmental health. The complex interplay of contributing factors highlights the need for a One Health approach in AMR mitigation. Improving antimicrobial stewardship (AMS) is an integral component of AMR mitigation success. Therefore, thesis objectives included: 1) describe the current state of AMR knowledge in Canada available in the literature, and identify the gaps in our understanding; 2) identify perspectives of AMS, including perceived drivers and barriers across the One Health spectrum of relevant Canadian professionals; 3) focus on the dairy industry as an example where AMS efforts are possible through selective dry cow therapy (SDCT); and 4) describe current SDCT uptake and related practices in the Canadian dairy industry. Current limitations in the understanding of AMR in Canada are described through a comprehensive review focussed on: 1) treatment optimization; 2) surveillance of antimicrobial use (AMU) and AMR; and 3) prevention of transmission of AMR. Whereas identified barriers to AMS described by Canadian professionals included: 1) lack of various prescribing and AMU support mechanisms; 2) shift in prescriber attitudes to drive change; and 3) stronger economic considerations to support shifting prescribing practices. Only treating cows who could benefit from antimicrobials at drying off (i.e., SDCT), represents an opportunity to reduce AMU in the dairy industry. A narrative review was conducted summarizing available literature regarding impacts of SDCT on udder health, milk production, economics, AMU motivations, and AMR. An observational study was conducted utilizing 2 in-person questionnaires between July 2019 and September 2021 on 144 dairy farms in 5 Canadian provinces. Overall, 31% reported adopting SDCT, with approximately 50% less intramammary AMU at drying off compared to treating all cows. A slight majority of farms (56%) applied teat sealants (TS) to all cows at drying off, whereas 12% used TS selectively, and 32% did not use TS. Results highlighted the variability in antimicrobial and TS use protocols at drying off on Canadian dairy farms, and the potential for further AMU reduction with increased SDCT adoption.
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    Modeling of Antimicrobial-Resistant Enterococci Exposure Risks in Canadian Beef Cattle Production System Using Existing Data
    (2024-04-17) Strong, Kayla; Checkley, Sylvia L.; Checkley, Sylvia L.; Kastelic, John Patrick; Otto, Simon James G.; Reid-Smith, Richard; Waldner, Cheryl Lynne; Lhermie, Guillaume; Noyes, Noelle
    Antimicrobial resistance occurs when microbes change, and antimicrobials previously used to treat them are no longer effective. Antimicrobial resistance presents a global risk to health and food safety, with previously treatable infections becoming increasingly costly and challenging. Antimicrobial resistance is a quintessential One Health issue, given its impact and drivers across human, animal, and environmental health, and requires transdisciplinary interpretations and solutions. This thesis considers methods of risk interpretation using a case study of antimicrobial-resistant Enterococcus spp. within Canadian beef production systems. Five objectives were considered: (1) to identify factors associated with antimicrobial-resistant enterococci within Canadian beef production systems; (2) to construct an integrated assessment model for interpretation of factors potentially associated with antimicrobial-resistant enterococci; (3) to construct a risk profile for interpretation of risks associated with antimicrobial-resistant enterococci in Canadian beef; (4) to construct a Bayesian model for interpretation of enterococci resistance within beef production; and (5) to describe integrated strengths and weaknesses of modeling approaches. Factors assessed for association with antimicrobial-resistant Enterococcus spp. within Canadian beef production systems included antimicrobial and nutritional supplement administration to cattle, environmental factors, and type of processing plant. Resistance trends were often nuanced to unique gene and phenotypic resistance. Patterns varied by species of enterococci. When data were available, the integrated assessment model utilized crude odds ratios extracted from identified factors. Limited data for baseline seeding and factor inclusion limited the model's interpretability. Recommendations and best practices are proposed for future model applications. The risk profile was developed to meet the Codex 77 guidelines and demonstrated the scarce evidence of enterococci resistance transference from beef products, and limited human pathogenicity of enterococci from foodborne consumption. The risk profile highlighted the need for Canadian surveillance studies of enterococci in food products for more informed decision-making. The Bayesian model incorporated available evidence with current estimates of enterococci resistance trends, integrating expert opinion within the model. The model suggests that less than 0.3% of beef products carry antimicrobial-resistant E. faecalis. Individual models and risk discussions uniquely fill niches in resistance discussions and interpretations but were insufficient for providing a holistic interpretation required by stakeholders across the production chain. Drawing findings from multiple reports supported a better understanding and enhanced decision-making.
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    Mycobacterium avium subsp. paratuberculosis: herd prevalence and calf-to-calf transmission
    (2018-05-10) Corbett, Caroline Susan; Barkema, Herman Wildrik; De Buck, Jeroen M.; Orsel, Karin; Kastelic, John Patrick; Buret, Andre G.
    Johne’s disease results in a progressive chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), leading to economic losses among dairy producers worldwide. In the absence of an effective vaccine to prevent infection and treatment for infected animals, control is primarily based on decreasing the number of new transmissions within a herd. Control programs have been implemented in countries and regions around the world; however, comparisons among prevalence estimates of difference regions and control programs are difficult and unreliable due to different tests used to identify infected animals and herds. Therefore, the first objectives of this thesis were to elucidate the influences of environmental sample characteristics on the outcome status of a herd, and to estimate the prevalence of MAP based on 2 environmental samples (and 3 environmental samples when including young stock) in Canada. Six environmental samples were collected twice, 3.5 years apart, from 148 dairy farms to determine whether difference in prevalence between sampling periods were associated with herd size and sample characteristics. All environmental samples regardless of type, had decreased odds of testing positive in the second sampling, and the largest herds had increased odds of testing positive than smaller herds at both sample periods. Across 4 regions (10 provinces) in Canada, 2 environmental samples, one from the lactating cow area and one the manure storage, were collected from 362 dairy farms, with an additional sample collected from breeding age heifers. Prevalence was lowest among tie-stall herds, in herds ≤ 100 cows, and in Québec; and although breeding age heifer samples did not affect prevalence estimates, they provided additional evidence that young stock are shedding MAP on farm. Therefore, the second objectives of this thesis were to determine the extent to which calf-to-calf transmission occurs among group-housed penmates, and to quantify the amount of fecal shedding that occurs among these infectious calves. An experimental transmission study was conducted, where 32 newborn calves were grouped into 7 experimental groups of 4, consisting of 2 inoculated (IN), and 2 contact exposed (CE) calves, and 1 control pen with 4 non-exposed calves. Calves were group-housed for 3 months, during which fecal, blood and environmental samples were collected frequently. The based reproduction ratio (R0) was estimated as a parameter of transmission of MAP infection using a final size (FS) model with a susceptible-infected-recovered (SIR) model based on ELISA and tissue culture. In addition, transmission rate parameter () was estimated using a GLM with a susceptible-infected-susceptible (SIS) model based on fecal culture during group housing. Throughout group housing, all IN and CE calves had MAP-positive fecal samples, and although there was a difference between frequency of shedding, there was no difference between the quantities of MAP shed in feces. All IN calves had positive MAP-tissue samples, and 7 (50%) of CE calves had positive tissue samples. Based on fecal shedding, the basic reproduction ratio R0 for CE calves (R0CE) was 3.24 (95% CI: 1.14, 7.41). R0I (based on interferon- results from blood samples) was 0.90 (95% CI: 0.24, 2.59), and R0T (based on tissue) was 1.36 (95% CI: 0.45, 3.94). Additionally, the effects of freezing on the ability to identify MAP in tissue samples were found to be minor; however, there may be a greater effect for CE calves that should be considered when freezing tissue samples. In conclusion, environmental samples characteristics did not influence the infection status of a herd, and collecting 2 environmental samples could be used to estimate prevalence and compare differences among regions. Shedding calves transmit infection to fellow penmates; therefore, future control programs should consider monitoring and testing of young stock to further decrease new transmissions on farm.