Appraisal of Interpretation Criteria for the Comparative Intradermal Tuberculin Test for Diagnosis of Tuberculosis in Cattle in Central Ethiopia

Abstract

Accurate detection and removal of infected cattle, using immunodiagnostic tests such as the comparative intradermal tuberculin (CIDT) test, are the basis of control strategies for bovine tuberculosis (TB). According to the Office des Internationale Epizooties recommendation, the cutoff point for positivity of the CIDT test, calculated as the difference between skin thicknesses after bovine tuberculin (B) and avian tuberculin (A) injections (B ؊ A), is >4 mm. This cutoff point is used worldwide, although it is likely that local conditions influence test performance. Thus, this study was formulated to determine CIDT test cutoff points applicable to cattle in central Ethiopia. Receiver operating characteristic analysis was performed for the CIDT test, using data from 186 Bos indicus (zebu) and Bos taurus (Holstein) cattle. Detailed postmortem examination for the presence of TB lesions was used to define disease status. At a cutoff of >2 mm, CIDT test sensitivity was 69% (95% confidence interval [95% CI], 58.5 to 79%), while it was 59% (95% CI, 49 to 69%) at a cutoff of >4 mm. In contrast, specificities of the CIDT test at these two cutoff values were identical, at 97% (95% CI, 89 to 100%). Thus, the maximum sensitivity of the CIDT test can be realized using a >2-mm cutoff without affecting specificity. The apparent prevalence was significantly ( 2 ‫؍‬ 13.56; P < 0.001) higher at a cutoff of >2 mm (16.0%; n ‫؍‬ 5,424) than at a >4-mm cutoff (13.5%; n ‫؍‬ 5,424). Nonetheless, no significant difference ( 2 ‫؍‬ 2.15; P ‫؍‬ 0.14) in true prevalence was observed at a cutoff of >2 mm (19.6%) and at a cutoff of >4 mm (18.5%). Thus, our study demonstrates the importance of defining local, relevant cutoff values to maximize test sensitivity, and we suggest the application of the >2-mm cutoff for testing of cattle in central Ethiopia.The tuberculin skin test is the primary diagnostic test for tuberculosis (TB) in both humans and cattle. Tuberculins are crude antigen preparations derived from heat-killed cultures of mycobacteria and contain mixtures of proteins, polypeptides, nucleic acids, and substantial amounts of polysaccharides (4). The comparative intradermal tuberculin (CIDT) test involves the intradermal injection of tuberculins, purified protein derivatives (PPDs) from Mycobacterium bovis and Mycobacterium avium, and the subsequent detection of swelling and indurations at the injection site 72 h later. The relative change in skin thickness at the two sites is used to differentiate M. bovis infection from infection with nontuberculous mycobacteria. According to the Office des Internationale Epizooties (OIE) (27) recommendation, the difference between the increase in skin thickness following the intradermal administration of bovine PPD (B) and the increase in skin thickness following the intradermal administration of avian PPD (A), B Ϫ A, should be Ͼ4 mm for the animal to be considered positive for bovine TB (bTB). Thus, the OIE advocates the use of this cutoff point for the diagnosis of bTB in live animals. Nonetheless...

Prevalence of camel tuberculosis and associated risk factors in camels slaughtered at Akaki Abattoir, Ethiopia

“…After 72 hours, the skin thickness at the injection sites was measured and recorded. Results were interpreted according to the recommendations of the Office International des Epizooties (OIE, 2009) at ≥ 4 mm cut-off and also at ≥ 2 mm cut-off (Ameni et al, 2008). Thus, at cut-off ≥ 4 mm, if the increase in skin thickness at the injection site for bovine PPD (PPD-B) was greater than the increase in skin thickness at the injection site for avian PPD (PPD-A) and; If PPD-B minus PPD-A was < 4mm or ≥ 4mm, the animal was classified as negative, or positive for BTB, respectively.…”

Tuberculosis Infection in Cattle and Cattle Owners in North Eastern Parts of Ethiopia

“…As it is shown in Table 4, according to previous cut off proved by Ameni et al [22] of the tested cattle 10 (10/381) (2.63%) were positive for the test. Highest positivity (with a reading >4 mms) was recorded in Raya-Kobo Woreda, in Adis alem Kebele, where 5 (~8.…”

“…Of the positives females contribute 50% of skin test positivity. In general, according to Ameni et al [22] report among the ten positive cattle, 4 (40%), 1 (10%) and 5 (50%) cattle were positive for the test in Dega, Woina Dega and Kolla Woredas, respectively.…”

“…The results were interpreted according to the manufacturer recommendations [19] using the cutoff point for positivity of the test, that is >4 mms difference, calculated as the difference between skin thicknesses of bovine tuberculin (B) and avian tuberculin (A) injection sites (B -A). But, Ameni et al [22] reported >2 mm difference as positive in Ethiopia. Based on his report, the test was considered positive if the difference was greater than 2 mm.…”

“…Based on this, the prevalence of BTB in this study was 0.013 (95% CI, 1-03%). In another scenario when the cut of skin fold measurements is taken as >2 mms, according to Ameni et al, [22] the number of positive cattle recorded lifted to 10, which in turn raises the prevalence to 2.63%. Six (6/9, nearly 67%) individuals among nine who owned positive cattle and reported having a chronic cough were having the habit of drinking unboiled milk.…”