The Sensitivity of Gross Necropsy, Caudal Fold and Comparative Cervical Tests for the Diagnosis of Bovine Tuberculosis

Abstract

Bovine tuberculosis (bTb) was diagnosed in 22 cattle herds in the northeast comer of Michigan's lower peninsula. Of these 22 herds, 494 animals in 7 herds were examined by gross necropsy, histopathologic exam, mycobacterial culture, and polymerase chain reaction (PCR) assay performed only on samples that were histologically compatible for bTb. Results of culture and PCR assay interpreted in parallel were used as the reference test for calculation of the sensitivity of 1) the caudal fold test (CFT), 2) the caudal fold and comparative cervical skin tests used in series (CFTCCTSER), and 3) gross necropsy. Mycobacterium bovis was isolated from 43 animals. Using all 7 herds, the sensitivities of the CFT, the CFTCCTSER, and gross necropsy were 93.02%, 88.37%, and 86.05%, respectively. When the data were stratified by low- and moderate-prevalence herds, the sensitivities were 83.33%, 75.0%, and 83.33% in low-prevalence herds and 96.77%, 93.55%, and 87.10% in moderate-prevalence herds. The sensitivities of the 2 skin tests were slightly higher when 2 or more gross lesions were present, and the sensitivity of gross necropsy was significantly higher (P = 0.049). The sensitivity of the CFT was found to be notably higher than most estimates in other studies; however, a direct comparison was not possible because the amount of purified protein derivative and the reference methods were different in this study compared with other published studies. Although the sensitivities are high, 2 of the 7 herds (29%) would have had 1 or more positive animals left in the herd if a test-and-removal program had been used. This suggests that when positive herds are identified, selective culling of skin test reactors is a less acceptable disease control strategy than is complete depopulation.

Post-mortem examination and laboratory-based analysis for the diagnosis of bovine tuberculosis among dairy cattle in Ecuador

“…However, the true prevalence, taking into account the Se (83.33%) (Norby et al, 2004) and Sp (95%) calculated for this method, was lower (1.50%). As this study was the first of its kind in the Mejia canton, we cannot compare our results with previous data of this region, even though it is the most important dairy region in the north of Ecuador.…”

“…This approach makes possible inferences about Se and Sp with 95% probability interval (95% PI) of necropsy used in this study. The prior distribution on Se was elicited from a previous study that considers the most likely value (modal), thus the Se of necropsy was 0.8 with a 10th percentile of 0.55; which is acceptable for this test and was chosen because a similar procedure during the necropsy was performed in the same lymph nodes (Norby et al, 2004), and based on the same measures through veterinary inspection to discard carcasses in Ecuador (Personal communication). The prior distribution for the Sp was elicited from the experience of veterinarian inspectors from the slaughterhouse of the Mejia canton, taking into account the presence of other infectious diseases causing lesions in lymph nodes specially in dairy cattle, thus a modal value of 0.95 with a 5th percentile of 0.80 were set to model the uncertainty about Sp.…”

“…Additionally the effect of different prior distributions for the parameters of the model was analyzed in order to evaluate how prior beliefs could affect the posterior estimates of TP, Se and Sp. Seven scenarios were built assuming prior different beliefs about the parameters (Table 1): (Scenario 1) No prior constraints: TP ∼ Uniform (0, 1), Se ∼ Uniform (0, 1) and Sp ∼ Uniform (0, 1); (Scenario 2) Prior distributions for Se and Sp uniformly distributed according to ranges suggested by Norby et al (2004), and expert opinion of veterinaries in slaughterhouses TP ∼ Uniform (0, 1), Se ∼ Uniform (0.51, 0.98) and Sp ∼ Uniform (0.80, 0.90); (Scenario 3) True prevalence constrained uniformly to values less that 10% and Se and Sp with similar values to previous experiences TP ∼ Uniform (0, 0.10), Se ∼ Uniform (0.50, 1.00) and Sp ∼ Uniform (0.70, 1.00); (Scenario 4) True prevalence constrained uniformly to values less that 5% and Se and Sp with similar values to previous experiences but widen: TP ∼ Uniform (0, 0.05), Se ∼ Uniform (0.40, 1.00) and Sp ∼ Uniform (0.60, 1.00); (Scenario 5) Assuming that Se of the necropsy is 70% and Sp 80% but with high uncertainty TP ∼ Uniform (0, 1.00), Se ∼ Beta (8.00, 4.00) and Sp ∼ Uniform (9.00, 2.00); Scenario 6) Assuming that Se of the necropsy is 70% and Sp 80% but with low uncertainty TP ∼ Uniform (0,1), Se ∼ Beta (71.0, 31.0) and Sp ∼ Uniform (86.0, 16.0); and finally (Scenario 7) TP ∼ Uniform (0, 1), Beta (5.28, 2.07) and Beta (21.20, 2.06) which correspond to our beliefs about necropsies. The agreement among the different laboratory-based diagnostic methods applied in this study was assessed by Cohen kappa statistic under cluster sampling (svykappa function) under R environment, described by Lumley (2004), which is the approach used to asses different tests without assuming that one is the best.…”

“…Compared to the recently observed CITT-based prevalence data among dairy cattle from the Mejia canton (Proaño-Pérez et al, 2009), our veterinary-inspectionbased prevalence was lower. This could reflect the lower sensitivity of post-mortem examination (Norby et al, 2004), implicating that a high number of animals might be classified as negative by this method. Routine abattoir inspection can be affected by the method employed, the anatomical sites examined and the stage of infection (Corner, 1994); it will fail to detect infected animals if lesions are present in tissues not being inspected.…”

A Case Study of Bovine Tuberculosis in Calf in Albania

“…Young animals react less than adult animals in tests based in late hypersensitivity and serological test. Postmortem diagnosis is based on gross lesion characteristics, microscopic lesions, culturing and ZN staining (Norby, et al, 2004, Menin, et al, 2013.…”