Date of Award

2017

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Jim O'Mahony

Second Advisor

Dr. Riona Sayers

Abstract

Johne’s disease (JD) is an enteritis of ruminants with potential zoonotic implications. JD diagnosis and control present difficulties given JDs prolonged subclinical nature. In order to improve JD control in Ireland, PhD aims included conducting a national survey documenting high-risk husbandry practices employed on Irish farms, thereby targeting areas for improved management. Furthermore as JD has been associated with on-farm economic losses internationally, this research programme aimed to analyse production losses associated with testing JD ELISA positive on Irish dairy farms. A longitudinal study was also conducted to assess if successful JD control can be achieved using gold-standard protocols. Due to the prolonged nature of the disease, diagnosis of MAP is notoriously difficult. None of the available tests for MAP report perfect test sensitivity or specificity. A further complicating issue in Ireland is the high level of bovine tuberculosis (bTB) testing that is conducted. Multiple investigations relating to bTB-testing and its relationship with MAP diagnostics were conducted. Across all investigations, 312 farms were recruited, samples were collected from 4500 cows, and 10000 test results were generated (ELISA, PCR, faecal culture). Irish farms engaged in high-risk management practices facilitating JD transmission, however, no significant associations were identified between JD ELISA positivity and production parameters. On-farm sero-prevalence was decreased by implementation of gold standard protocols. Eradication was not achieved, however, highlighting the long-term commitment required for effective JD control. Annual bTB testing was associated with an increased prevalence of JD ELISA positive results and indicates that sampling for the purposes of JD surveillance should be avoided for 71 days post-TB test administration. Antibody responses and interferon-y production were significantly increased post-bTB testing. As cell-mediated immunity is particularly important in the control of JD systemically, bTB testing may be contributing to the low levels of clinical JD in Ireland and warrants further investigation. This research programme has greatly contributed to our knowledge of JD in Ireland and improves understanding of practical measures necessary to interpret ELISA diagnostics and aid JD control.

Access Level

info:eu-repo/semantics/openAccess

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