Author
|
Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/7/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Eradication of bovine tuberculosis (TB) is important because of public health and trade issues. Final eradication of bovine TB has been hindered in the U.S. in recent years due to multiple factors including inability to depopulate very large infected dairy herds and importation of infected cattle from Mexico. Improved diagnostic tests are needed to identify infected herds and individual infected animals, so they can be eliminated and/or not imported into the United States. The Bovine Gamma Interferon (gIFN) Test, which measures an immune response, has been approved as a supplemental test for diagnosis of TB in cattle; its performance as a tool in the U.S. Bovine TB Eradication Program is still being assessed. Cattle under stress in certain production and shipping situations may have a suppressed immune response. In this study, using an experimental model of stress in cows with TB, false negative results in the gIFN test were observed. These results indicate that cattle with TB may not be detected b the gIFN test if samples are collected from animals that are stressed, such as after shipping, or that have been treated with certain commonly used anti-inflammatory drugs. The results have implications for the management, shipping conditions, and medical treatment schedule under which samples for the gIFN Test are collected from cattle, and provide information for the assessment of the gIFN test for use in the Eradication Program. Technical Abstract: The effect of dexamethasone (DEX) treatment on results of a commercial Mycobacterium bovis gamma-interferon (gIFN) test was examined. The gIFN test is an enzyme immunoassay of plasma from bovine whole blood samples that have been cultured with M. bovis and M. avium tuberculin purified protein derivatives (PPDs); it is approved as a supplemental test for diagnosis of bovine tuberculosis. Blood was drawn prior to, during, and after three days of DEX treatment in naturally-infected cows. gIFN tests results were evaluated by optical density (OD), and by three OD calculation methods. Before DEX treatment, all cows had positive gIFN tests by each calculation method. As early as 24 hr after the first DEX injection, PPD stimulated gIFN production decreased in samples from all cows, as reflected in OD data. Calculated gIFN test results were negative after DEX treatment for all but one cow, which produced relatively large amounts of gIFN. Degree of suppression of gIFN production, and number of days gIFN test results were negative after DEX treatment (1-8 days), varied by cow and by data calculation method. Treatment with DEX is associated with suppressed PPD-stimulated gIFN production, which may be reflected as false negative results in the gIFN test depending on the data calculation method applied. Results have implications for the management conditions and medical treatment schedule under which samples for the gIFN test are collected. |
