Seroprevalence of Mycobacterium avium subsp. paratuberculosis (MAP) and associated risk factors in Northern Ireland dairy cattle herds

Abstract Background Johne’s disease is a chronic granulomatous enteritis of cattle and other ruminants of economic, animal and public health significance, caused by Mycobacterium avium subsp. paratuberculosis . It is endemic in UK, but there is currently limited information in Northern Ireland. To address this gap, for the first time surveillance data were used to estimate seroprevalence and explore risk factors for a cohort of herds that participate in a voluntary scheme. Methods A Bayesian approach, Gibbs sampling was used to estimate animal-level true prevalence. The effects of test sensitivity, specificity, and true prevalence and number of animals tested and critical number of positive reactors were considered for herd test sensitivity, specificity and true prevalence estimation. Logistic regression was used to develop a model associating herd status with putative risk factors. Results 46,715 cattle in 431 dairy herds were tested by ELISA between 2010 and 2019. 2138 (4.6%) animals were positive. At least one ELISA-positive case was detected in 239 herds (55.4%, 95%CI: 50.7 - 60.1) whereas, 152 herds recorded ≥2 ELISA-positives (35.2 %, 95% CI: 30.7 - 39.8). The mean true herd prevalence was estimated to be 34.7% and 43.9 % for k ≥1 and k ≥2 critical number of reactor herds respectively. The study estimated 9.5 % (95%PPI: 0.5 - 21.4), 32.8 % (95 % PPI: 17.1 - 50.8) and 98.3 % (95 % PPI: 95.6 - 99.9), median values for animal-level true prevalence, test sensitivity and specificity respectively.Herds sized ≥ 100 were between 1.8 and 5.5(95%CI: of the OR) times more likely to test MAP ELISA-positive than herds with < 100 cattle. Herds with mean animal age of ≥5 years were between 1.5 and 3.6 (95% CI: of the OR) times more likely to have MAP ELISA-positive results than herds with a mean animal age of < 5 years. Conclusion Results of this study estimated disease prevalence and identified some associated risk factors which improves understanding of the local epidemiology, and indicate the need for establishing a sustainable control programme. Further investigation is required to better understand local epidemiology and associated production and economic losses.