Seroprevalence study of paratuberculosis: Johne's disease, a neglected infection in dairy herds in Apulia (southern Italy)

Introduction: Paratuberculosis (PTB) is a disease caused by Mycobacterium avium subsp. paratuberculosis (MAP). In Italy, voluntary PTB control plans have been imple- mented; nonetheless, so far, data on the prevalence of PTB in dairy herds are fragmented and incomplete, especially in the south of the country. Objectives: The objectives were to determine the apparent (AP) and true (TP) prevalences of MAP infection, at the inter-herd (between-herd, BH) and intra-herd (within-herd, WH) levels, and the odds ratio (OR) to assess the probability of both cattle and herds testing positive in the provinces of Apulia, in southern Italy. Methods: A total of 6056 serum samples collected from 341 different dairy farms were analysed by ELISA. The number of farms and cattle required, BH and WH prevalence estimates, ORs, 95% confidence interval values (CIs) and p-values (p) were calculated. Results: A low overall TP was estimated at both the BH level (17.14%) and WH level (0.82%). Statistically significant differences in OR (p < 0.05) were found for the provinces of Foggia, with a high risk of positive animals at both BH (OR = 2.6569) and WH (OR = 2.5583) levels and Taranto, with a low risk at the WH (OR = 0.5043) level. Conclusions: Our results provide the first data on the prevalence of PTB in Apulian dairy herds, according to the following criteria: (i) use of a multi-step sample size calcu- lation procedure considering the test’s imperfection; (ii) selection of larger sample sizes of both herds; (iii) inclusion of herds and cattle from the Apulia region only recruited randomly; and (iv) analysis of the test results using non-Bayesian approaches