A lateral-flow immunoassay (BrockTB Stat-Pak) for detecting tuberculosis in Eurasian badgers was 49% sensitive and 93% specific against culture for M. bovis (n ‫؍‬ 1,464) at necropsy. However, the sensitivity was significantly higher (66 to 78%) in animals with more severe tuberculosis, indicating that the BrockTB Stat-Pak may be useful for the detection of badgers with the greatest risk of transmitting disease.Despite attempts to control bovine tuberculosis (TB), the average incidence of disease in cattle in Great Britain increased an estimated 225% between the years 1996 and 2006 (7), causing considerable economic loss to the government and the farming community. In parts of Great Britain and Ireland, Eurasian badger (Meles meles) populations constitute a reservoir of infection with Mycobacterium bovis and a potential source of infection to cattle (8,14,15). In an effort to simplify the serodetection of badger TB, we developed a lateral-flow immunoassay (13) that is now manufactured as the BrockTB Stat-Pak assay (Chembio Diagnostic Systems, Inc., Medford, NY). We report here the results of ongoing evaluation of the assay, in particular the influence of disease severity on diagnostic accuracy.Badger sera were obtained in Great Britain from two sources and stored frozen at Ϫ20°C until testing (i) 1,464 animals killed as part of the defra/Independent Scientific Group Randomized Badger Culling Trial (RBCT) (8) and (ii) 68 animals captured, sampled, and then released as part of an ongoing ecological and epidemiological study in Woodchester Park (WP), southwest England (6). Each badger from the RBCT was subjected to routine necropsy examination and culture for the presence of M. bovis. Carcasses were stored at 4°C and examined by a standardized necropsy protocol within 3 days of submission. A range of tissues and lymph nodes were examined for evidence of TB. In badgers with no lesions the bronchial, mediastinal, and retropharyngeal lymph nodes were placed in 1% cetyl-pyridinium chloride prior to bacterial culture. In badgers with lesions the lesion tissue was always submitted for culture. Bite wounds were sampled separately. Tissues were processed within 72 h of sampling. The cetyl-pyridinium chloride was discarded, and the tissues were rinsed in saline and then emulsified before inoculation onto six slopes of modified Middlebrook 7H11 agar. The slopes were incubated at 37 Ϯ 2°C. Any growth of organisms characteristic of mycobacteria was identified by spoligotyping (9). The infection status of WP badgers was determined by bacterial culture of clinical samples of feces, urine, sputum, pus from abscesses, and bite wound swabs as described previously (3).Compared to the culture results from tissues taken at necropsy (n ϭ 1,464), the findings were as follows: BrockTB StatPak positive, culture negative, n ϭ 74; BrockTB Stat-Pak negative, culture negative, n ϭ 1,004; BrockTB Stat-Pak positive, culture positive, n ϭ 190; and BrockTB Stat-Pak negative, culture positive, n ϭ 196. Thus, the BrockTB Stat-Pak had a sensitivity ...

BackgroundIn parts of Great Britain and Ireland, Eurasian badgers (Meles meles) constitute a reservoir of Mycobacterium bovis infection and a potential source of infection for cattle. In vitro diagnostic tests for live badgers are an important component of strategies to control TB in this species. Immunological tests have been developed for badgers, although little is known about the influence of the age of the animal on test performance. To address this, we evaluated the performance of three immunological tests for badgers with respect to the age of the animal: the Brock Test and BrockTB STAT-PAK® serological tests and the recently developed interferon-gamma enzyme immunoassay (IFNγ EIA). Data published elsewhere suggested that seropositivity was associated with more progressive forms of TB in the badger. To gain further evidence for this, we used longitudinal data from a well-studied population of badgers to test for an association between the sensitivity of the Brock Test and the duration of TB infection.ResultsSensitivity of the two serological tests was approximately 54% for both cubs and adults. Sensitivity of the IFNγ EIA was lower in cubs (57%) compared with adults (85%) when a common cut-off value was used to define test positivity. Taking data from the cubs alone, the IFNγ EIA cut-off value could be adjusted to increase the sensitivity to 71% with no loss in specificity. As a general observation, specificity of all tests was higher in cubs, although only significantly so in the case of the Brock Test. Using logistic regression analysis to adjust for age, sensitivity of the Brock Test was significantly lower at first culture positive event (58%), but increased to >80% as infection progressed.ConclusionThese data suggest that serodiagnosis could be a valuable tool for detecting a higher proportion of badgers with the greatest probability of transmitting infection. The age category of the badger appeared to exert little influence on the performance of the serological tests. Although data were only available for the IFNγ EIA in a small number of cubs, reduced sensitivity of the test in these individuals suggests a lower cut-off may be needed when testing younger animals.