Evaluation of Surveillance for Documentation of Freedom from Bovine Tuberculosis

The objective was to study how surveillance for bovine tuberculosis (bTB) could be made more resource-effective in a bTB free country. A stochastic scenario tree model was developed to: (1) evaluate the sensitivity (CSe) of four surveillance system components (SSC) ( i.e. , meat inspection of slaughtered domestic cattle, farmed deer and pigs, and tuberculin testing of adult export cattle) given that bTB would enter one of these components, (2) estimate the probability of freedom (PFree) from bTB over time, and (3) evaluate how future alternative programmes based on visual meat inspection would affect the confidence in freedom from bTB at the very low animal-level design prevalence 0.0002% and a low probabilities of introduction (1%). All, except the export cattle component reached a PFree above 96% within five years. The PFree was slightly reduced if surveillance was changed to visual inspection, e.g., PFree was reduced from 96.5% to 94.3% in the cattle component, and from 98.5% to 97.7% in the pig component after 24 years. In conclusion, visual meat inspection of pigs and cattle will only reduce the confidence in freedom from bTB slightly. However, with negligible probability of introduction (0.1%) the PFree could be maintained well above 99% in the cattle, pigs and deer components, which highlights the importance of rigid testing and quarantine procedures in trade of livestock.