Submitted to: Veterinary Record
Publication Type: Other
Publication Acceptance Date: 5/24/2012
Publication Date: 5/25/2012
Citation: Waters, W.R. 2012. Bovine TB and the 'singleton protocol': reward without risk. Veterinary Record. 2012(170):514-515.
Interpretive Summary: Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is increasing in cattle in the US, UK, and the Republic of Ireland and causes serious trade hindrances. Control of bTB is complicated by the presence of numerous wildlife reservoirs such as white-tailed deer, European badgers, and brush-tailed possums. Reasons for the failure to eradicate the disease are multi-factorial. Limitations in the sensitivity and specificity of diagnostic tests are factors contributing to the persistence of bTB. Test interpretation and accuracy are confounded by variations in the frequency of tuberculin testing, ambiguities in test result interpretation, and the use of varying tuberculin preparations. In the present report, a scientific editorial is provided to discuss the ramifications of use the ‘Singleton Protocol’ to enable earlier restoration of health status for herds at low risk with a single bTB reactor animal. These findings will provide positive financial implications for Irish producers.
Technical Abstract: The ‘Singleton Protocol” was initiated in 1996 by the Irish Department of Agriculture Fisheries and Food to address the shortfall in specificity of the single intradermal comparative cervical test (SICCT) for bTB. Findings from Murray et al., demonstrate that singleton candidates (i.e., from low risk herds meeting test criteria) had a significantly (P < 0.001) lower lesion rate compared with non-candidate single reactors (43.2% versus 61.9%). While the ‘Singleton Protocol’ does not influence reactor retest results (i.e., singleton herds did not differ from non-singleton reactor herds), the study reaffirms (Good and Duignan, 2011) the low rate of herd breakdowns (i.e, ~6 - 8%) upon retest of singleton reactor herds as previously demonstrated by Olea-Popelka (2004). Additional risk factors identified were size of induration upon SICCT and animal origin in regards to bTB prevalence. The risk was 7.6X greater for animals with a skin test response of > 12 mm (difference in M. bovis and M. avium PPD response) as compared to 1 to 5 mm difference. Herds within districts with bTB incidence rates in the three upper quartiles had > 7X retest breakdown rates as compared to those herds in the lowest quartile. Thus, the qualifying criteria are effective in identifying lower risk herds. Overall, Murray et al demonstrate that early restoration of singleton herds to disease free status does not incur an increased risk for herd retest breakdown. The ‘Singleton Protocol’ provides positive financial implications for cattle producers; thus, this policy provides reward without significant risk.