Evaluation of Three Commercial Interferon-γ Assays in a Bovine Tuberculosis Free Population

Abstract

The interferon-γ assay has been used worldwide as an ancillary test for the diagnosis of bovine tuberculosis (bTB). This study aimed to describe, based on the bTB-free status in Switzerland, the difference of applying a more stringent cutoff point of 0.05 compared with 0.1 for bTB surveillance. Moreover, the effect of time between blood collection and stimulation, culture results, optical density values, and the influence of testing different breeds were evaluated. Blood samples from a total of 118 healthy cows older than 6 months were tested with three commercial interferon-gamma assays. To confirm the bTB-free status of the tested animals and to investigate potential cross-reactions with nontuberculous mycobacteria, pulmonary and abdominal lymph nodes in addition to ileal mucosa from each cattle were used for the detection of viable Mycobacteria spp. by specific culture. Significant differences regarding the proportion of false-positive results between the two Bovigam tests and between Bovigam 2G and ID Screen were found. Samples analyzed with Bovigam 2G were 2.5 [95% confidence interval (CI) 1.6–3.9] times more likely to yield a false-positive test result than samples analyzed with Bovigam TB. Similarly, the odds ratio (OR) for testing samples false-positive with ID Screen compared with Bovigam TB was 1.9 (95% CI 1.21–2.9). The OR for testing false-positive with ID Screen compared with Bovigam 2G was less to equally likely with an OR of 0.75 (95% CI 0.5–1.1). When using a cutoff of 0.05 instead of 0.1, the OR for a false-positive test result was 2.2 (95% CI 1.6–3.1). Samples tested after 6 h compared with a delayed stimulation time of 22–24 h were more likely to yield a false-positive test result with an OR of 3.9 (95% CI 2.7–5.6). In conclusion, applying a more stringent cutoff of 0.05 with the Bovigam 2G kit generates a questionable high number of false-positive results of one of three tested animals. Furthermore, specific breeds might show an increased risk to result false-positive in the Bovigam 2G and the ID Screen assays.

Comparative diagnosis of bovine tuberculosis using single intradermal cervical tuberculin technique, conventional methods, enzyme-linked immunosorbent assay, and the gamma-interferon assay

“…Furthermore, it can be immediately repeated on the same animal, which can only be handled once [ 7 ]. The IFN-γ test is also directed to specific antigens absent in Bacillus Calmette-Guerin or other non-tuberculous mycobacteria [ 37 ].…”

“…However, the tuberculin test is limited by variable specificity and sensitivity due to common skin reactive antigens that cause reactions in animals sensitized to non-tuberculous mycobacteria [ 6 ]. Others disadvantages of tuberculin test include the individual variation in test performance in injection, measurement ability, and test interpretation [ 7 ]. Alternative laboratory tests have been developed to overcome the drawbacks of the tuberculin test [ 8 ], including serological methods like the enzyme-linked immunosorbent assay (ELISA).…”

“…The gamma-interferon (IFN-γ) assay has been developed and used either alone or as an ancillary to the tuberculin test in TB diagnosis [ 10 ]. The IFN-γ assay has many advantages over the tuberculin test, such as early diagnosis of infected animals in endemic areas and easy standardization and interpretation [ 7 ].…”

Infection of a Free-Living Wild Boar (Sus scrofa) with a Bacterium from the Mycobacterium kansasii Complex

“…Mycobacteriosis caused by MKC may also misrepresent the individual's disease status in skin tests and other assays used in the diagnosis of tuberculosis in animals and humans and produce false positive results. This fact significantly complicates the treatment process in humans and is the reason for wrong decisions to slaughter the animal [42][43][44].…”

Effect of a recent parenteral dexamethasone and ketoprofen administration on the immunological diagnosis of tuberculosis in goats

“…Both of these techniques, which are based on the cellular immune response, are valuable diagnostic tools, although they are not perfect in terms of sensitivity and specificity, and several factors could affect their performance ( 11 – 15 ). One of these factors is the administration of anti-inflammatory substances, which are, according to previous studies in goats ( 16 ) and cattle ( 17 , 18 ), able to modify the results of official TB diagnostic tests carried out in ruminants.…”