Abstract
Denmark has not had cases of bovine tuberculosis (bovTB) for more than 30 years but is obliged by trade agreements to undertake traditional meat inspection (TMI) of finisher pigs from non-controlled housing to detect bovTB. TMI is associated with higher probability of detecting bovTB but is also more costly than visual-only inspection (VOI). To identify whether VOI should replace TMI of finisher pigs from non-controlled housing, the cost of error – defined here as probability of overlooking infection and associated economic costs - should be assessed and compared with surveillance costs. First, a scenario tree model was set up to assess the ability of detecting bovTB in an infected herd (HSe) calculated for three within-herd prevalences, WHP (1, 5 and 10%), for four different surveillance scenarios (TMI and VOI with or without serological test, respectively). HSe was calculated for six consecutive 4-week surveillance periods until predicted bovTB detection (considered high-risk periods HRP). 1-HSe was probability of missing all positives by each HRP. Next, probability of spread of infection, Pspread, and number of infected animals moved were calculated for each HRP. Costs caused by overlooking bovTB were calculated taking into account Pspread, 1-HSe, eradication costs, and trade impact. Finally, the average annual costs were calculated by adding surveillance costs and assuming one incursion of bovTB in either 1, 10 or 30 years. Input parameters were based on slaughterhouse statistics, literature and expert opinion. Herd sensitivity increased by high-risk period and within-herd prevalence. Assuming WHP=5%, HSe reached median 90% by 2nd HRP for TMI, whereas for VOI this would happen after 6th HRP. Serology had limited impact on HSe. The higher the probability of infection, the higher the probability of detection and spread. TMI resulted in lowest average annual costs, if one incursion of bovTB was expected every year. However, when assuming one introduction in 10 or 30 years, VOI resulted in lowest average costs. It may be more cost-effective to focus on imported high-risk animals coming into contact with Danish livestock, instead of using TMI as surveillance on all pigs from non-controlled housing.
Highlights
Denmark has been officially free from bovine tuberculosis (OTF) since the first declaration in 1980
Assuming within-herd prevalence (WHP) = 5%, herd sensitivty (HSe) reached 90% by the 2nd herd prevalence and time period* (HRP) for traditional meat inspection (TMI), whereas for visual-only inspection (VOI) this would only happen after the 6th HRP
The work undertaken illustrates a hypothetical situation, where bovTB is introduced to Danish non-controlled pigs, and where a subsequent detection by different surveillance approaches has economic consequences depending on the spread of disease before detection, control measures implemented thereafter, and reaction of TABLE 4 | Median probability of spreada of bovine tuberculosis from one hypothetical infected pig herd to one or more pig herds as well as number of moved infected pigs, divided according to time period (HRP) after introduction, while assuming a within-herd prevalence of 1, 5 or 10%
Summary
Denmark has been officially free from bovine tuberculosis (OTF) since the first declaration in 1980. The last detected, positive cases of bovine tuberculosis (bovTB) were seen in farmed deer in 1994 [1] and traced back to imported deer. The year of the last case of bovTB in Danish pigs is unknown, but it has not been detected for decades In the United Kingdom, which is not OTF, pigs are found positive for bovTB sporadically; from 2000 to 2010, between 0 and 29 pigs were found positive for bovTB annually [4]. This low number is probably a result of a spill-over from infected cattle or wildlife. Pigs usually serve as dead-end-hosts for M. bovis
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