ABSTRACT
Between December 2002 and April 2006, 114 cattle farms in the south west of England were visited at least once, with 100 farms visited three times. A total of 29,782 serum samples were collected from 15,736 individually identified cattle. The sera were tested for the presence of antibodies against Mycobacterium avium subsp. paratuberculosis (MAP) using an indirect enzyme-linked immunosorbent assay (ELISA). The mean seroprevalence in herds sampled three times was 7.1%; 10.1% of cattle had at least one positive result. There were 78%, 75% and 75% dairy herds with at least one positive bovine at the first, second and third routine visits, respectively. In comparison, 44%, 42% and 46% suckler herds had at least one positive bovine for the first, second and third routine visits, respectively. In most herds (>90%), within herd seroprevalence of MAP remained stable over time. Markov chain Monte Carlo (MCMC) simulation methods were used to re-estimate the test sensitivity and specificity. The sensitivity results were 33.3% (95% CI, 28.8-37.8%), 34.5% (95% CI, 30.3-38.8%) and 34.8% (95% CI, 30.8-38.9%) for the first, second and third routine visits and the specificity results were 99.7% (95% CI, 99.3-99.9%), 99.8% (95% CI, 99.4-99.9%) and 99.7% (95% CI, 99.3-99.9%) for the first, second and third routine visits, respectively. The expected true prevalence was also estimated, 11 (21.1%) suckler herds and 1 (2.1%) dairy herd were predicted to be truly free from infection during the study period. The seroprevalence of antibodies against MAP increased with cattle age. There was a significantly higher seroprevalence of MAP in dairy breeds of cattle compared with suckler breeds of cattle. This was more pronounced in Channel Island breeds. Smaller dairy herds (<100 cattle) had a relatively lower seroprevalence of MAP than dairy herds with >/=100 cattle. In 8 (42%) of the 19 herds with > or =100 cattle born into the same herd, seropositive cattle were clustered by birth month whilst in the remaining herds clustering was not apparent. Daughters were significantly more likely to be MAP seropositive when born to a seropositive dam.
