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. 2009 Mar 1;62(3):182-90.
doi: 10.1186/2046-0481-62-3-182.

An evaluation of Irish cattle herds with inconclusive serological evidence of bovine brucellosis

M Hayes  1 , S Ashe, Dm Collins, S Power, K Kenny, M Sheahan, G O'Hagan, Sj More
Affiliations

An evaluation of Irish cattle herds with inconclusive serological evidence of bovine brucellosis

M Hayes et al. Ir Vet J. .

Abstract

Since 1998, there has been a steady decline in herd restrictions and de-populations in Ireland due to bovine brucellosis. There is concern that the interpretation of laboratory results may become increasingly problematic, as brucellosis prevalence falls in Ireland. Therefore, the purpose of the current study was to evaluate the infection status of Irish herds and animals with inconclusive serological evidence of bovine brucellosis. During 12 months from September 1, 2004, laboratory and observational epidemiological data were collected from all Irish herds where animal testing identified at least one animal with a complement fixation test (CFT) reading greater than zero and/or a positive result to the indirect enzyme-linked immunosorbent assay (iELISA). Due to the observational nature of the study, we have robust estimates of the relative, but not the absolute, performance of the CFT, iELISA and brucellin skin test (BST). Herds were divided into three categories (Group A, B or C) on the basis of test results at initial assessment. A total of 639 herds were enrolled into the study, and observed for at least two years following enrolment. A rising CFT titre, with a CFT reading of 111 International CFT Units (IU) or greater at the subsequent blood test, was generally associated with herds where other evidence of infection was also available. Knowledge of the CFT reading at the initial and a subsequent blood test proved useful in distinguishing false-positive and true-positive brucellosis results. There was poor correlation between the CFT and iELISA results, and between the CFT and BST results. As a result of this study, national policy has been modified to include re-sampling of all animals with CFT readings of 20 IU or greater. This project has also led to a reduction in the number of herds restricted, as well as restriction duration. It has also contributed to a reduction in the number of herds listed for contiguous tests, and therefore the potential for contiguity testing of false positive results.

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Figures

Figure 1
Figure 1
National policy changes, relevant to the eradication of bovine brucellosis, between 1965 and 2004.
Figure 2
Figure 2
New herd restrictions and depopulations due to bovine brucellosis in Ireland during 1994 to 2007. Herd depopulation data was not available for 1994 and 1995.
Figure 3
Figure 3
A flow diagramme highlighting the protocol for annual herd testing in Ireland, the process of herd categorisation in this study, and the diagnostic tests applied to the different study groups. A range of diagnostic tests are mentioned, including the microtitre serum agglutination test (MSAT), complement fixation test (CFT), the indirect enzyme-linked immunosorbent assay (iELISA) and the brucellin skin test (BST).
Figure 4
Figure 4
The location of the study herds.
Figure 5
Figure 5
Risk factors and diagnostic test results at the subsequent assessment for 334 study animals in 198 Group B herds. A range of diagnostic tests are mentioned, including the complement fixation test (CFT), the indirect enzyme-linked immunosorbent assay (iELISA) and the brucellin skin test (BST).
Figure 6
Figure 6
Risk factors and diagnostic test results for 252 animals in 244 Group C herds. A range of diagnostic tests are mentioned, including the complement fixation test (CFT), the indirect enzyme-linked immunosorbent assay (iELISA) and the brucellin skin test (BST).
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References

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