Relative effectiveness of Irish factories in the surveillance of slaughtered cattle for visible lesions of tuberculosis, 2005-2007

Abstract

BackgroundIn Ireland, every animal is examined at slaughter for its fitness for human consumption. The aim of this study was to determine the relative effectiveness of factories in submitting and subsequently in having suspect lesions confirmed as bovine tuberculosis (TB) lesions during the years 2005-2007. This work provides an update from previously published data for years 2003-2004. During 2005-2007 data were available on 4,401,813 cattle from attested herds (i.e. herds classified free of bovine TB), from which data for potential confounding factors were available for 3,344,057 slaughtered animals at one of the 37 export-licensed factories.FindingsFrom these animals, 8,178 suspect lesions were submitted for laboratory confirmation. Lesions from 5,456 (66.7%) animals tested as positive, and 269 (3.2%) were inconclusive for bovine TB. Logistic regression was used to determine adjusted submission and confirmation risks for each factory while controlling for confounding factors. Factory rankings based on adjusted and crude risks were similar. The average crude submission risk for all the factories was 25 lesions per 10,000 animals slaughtered, ranging from 0 to 52. The crude confirmation risk varied between 30.3% and 91.3%.ConclusionsSubstantial variation in the effectiveness of lesion submission and subsequent confirmation as bovine TB was found among the 37 factories. Compared to previous years (2003-2004), there was an increased bovine TB lesion submission and confirmation risk. Continued monitoring of the effectiveness of slaughter surveillance in Ireland is recommended; emphasis should be placed on efforts to improve bovine TB surveillance in factories with lower rankings.

Understanding and managing bTB risk: Perspectives from Ireland

“…Collins (1997) suggests that variations in factory surveillance efficiency may be due to factory-related circumstances, for example, line speed and light intensity, and/or to factors related to the veterinary inspector, for example, their experience, interest, motivation and workload. In a later study, using equivalent data from 2005 to 2007, improvement was evident, including an observed 5-fold difference in submission risk between abattoirs (range 11-58 per 10,000, average 25 per 10,000; Olea-Popelka et al, 2012). Between 2006 and 2012, the submission risk rose from 26.8 to 37 per 10,000, whereas the confirmation risk fell from 18.2 to 14.9 per 10,000.…”

Risk factors for visible lesions or positive laboratory tests in bovine tuberculosis reactor cattle in Northern Ireland

“…Several studies (Frankena et al, 2007;Olea-Popelka et al, 2012;Shittu et al, 2013;Wright et al, 2013) There isn't a specific and defined time frame for the development of the different curves in Figure 2 since a number of variables including the route of infection, the infectious dose and host related factors will determine the onset and development of the antimycobacterial response .…”

“…The sensitivity of gross post-mortem examination depends on the method employed and the anatomical sites examined. The detection rate of visible lesions varies significantly between abattoirs (Frankena et al, 2007;Olea-Popelka et al, 2012;Shittu et al, 2013;Wright et al, 2013). In Northern Ireland all reactors with visible lesions are subjected to histology examination of which the majority shows tuberculoid granulomata.…”

Scientific Opinion on the public health hazards to be covered by inspection of meat (bovine animals)

“…Comparisons between the results, however, are difficult, partly because a common gold standard is not available and partly because inspection procedures may vary in efficiency between slaughterhouses and inspectors (Martin et al, 2003;Frankena et al, 2007;Biffa et al, 2010;Olea-Popelka et al, 2012).…”

“…The proportion of cattle showing lesions and the proportion of suspected lesions which are in fact due to M. bovis (confirmation rate) are affected by the prevalence on infection in an area, and by factors related to the slaughterhouse and laboratory (Corner et al, 1990;Frankena et al, 2007;Olea-Popelka et al, 2012). The proportion of skin test reactors not showing lesions may be as high as 10 % after a detailed necropsy (Corner, 1994), and as high as 60 % applying current MI procedures (Costello et al, 1997;Karolemeas et al, 2012 The importance of this process of confirmation of infection is higher when the prevalence of bTB is further reduced.…”