MODELLING WITHIN-HERD TRANSMISSION OF PARATUBERCULOSIS INAN IRISH DAIRY HERD: INFECTION DYNAMICS AND THE EFFECT OF TESTINGAND CULLING

摘要

Johne's disease is a chronic bacterial infection of cattle caused by Mycobacterium avium subspecies paratuberculosis {Map), inducing large economic losses to farmers. We simulated Map transmission in Irish dairy herds with a seasonal pasture-based milk production system and compact spring calving. We used this stochastic model to investigate Map persistence, relative importance of transmission routes, and effectiveness of control measures. Mean within herd prevalence in absence of control measures 15years after Map introduction was 63.5%. The main transmission routes were a contaminated general environment and in utero infection. The most effective control measures were culling all high shedding test positive animals within 4 weeks after testing (28% absolute decrease in prevalence after 15 years) and managing calf exposure by separating calves from cows on pasture (15% absolute decrease in prevalence). Both control measures effectively reduce persistence and slow the rate with which prevalence increases over time.