Development and diagnostic validation of an ELISA based on an antigenic mixture for the detection of bovine tuberculosis

Programs for the eradication of bovine tuberculosis (bTB) focus on the tuberculin skin test (TST) and slaughter of reactor cattle. However, the disease remains an animal health concern in several countries and improving the efficiency of the TST has become a critical issue. The detection of Mycobacterium bovis antibodies in serum, within weeks after the TST, may be a rapid and inexpensive way to improve bTB control. This study reports the validation of an enzyme-linked immunosorbent assay (ELISA) to detect bovine tuberculosis as an ancillary test to TST in dairy farms in Argentina. The estimated validation parameters were within the established requirements of the World Organization for Animal Health (OIE). The test demonstrated high repeatability, with coefficients of variation <25%. High test reproducibility through interlaboratory testing was also found, with an estimated Pearson coefficient of 0.9648 (95% confidence intervals 0.9315-0.9820). The ELISA detected tuberculous cattle unidentified by the TST. Of 43 animals sent to slaughterhouses that were ELISA positive 15-17 days after a negative TST, 36 were confirmed as infected with M. bovis by histopathology and IS6110 PCR. According to ROC curve analysis of results of 145 cattle from M. bovis-free herds and the 36 M. bovis-infected cattle, at a corrected optical density cut-off point of 0.3853, specificity was 95.95% and the positive predictive value at this cut-off was 83.72%. The ELISA detection test validated in this study could be readily applied in dairy farms, to complement a prior TST and improve livestock health.

Comparison of reverse-transcription real-time PCR and immunohistochemistry for the detection of canine distemper virus infection in raccoons in Ontario, Canada

Canine distemper virus (CDV) is a widespread morbillivirus that causes subclinical to fatal infections in domestic and wild carnivores. Raccoons ( Procyon lotor) are CDV reservoirs and suffer from associated disease. Aspects of pathogenesis may lead to difficulty in the interpretation of commonly used testing modalities, such as reverse-transcription real-time (RT-rt)PCR and immunohistochemistry (IHC). The reliance upon such tests is greater for wildlife, which are often submitted as carcasses with no clinical history. We compared CDV RT-rtPCR results to immunohistochemistry (the gold standard) in tissues from 74 raccoons. These tests had high kappa agreement (lymph node: 0.9335; lung: 0.8671) and a negative correlation between IHC score and threshold cycle (Ct) value for lymph node and lung (Spearman rank correlation coefficient [ r_s] = -0.8555 and -0.8179, respectively; p < 0.00001). An RT-rtPCR Ct value of 30 in lung and lymph node with sensitivity and specificity of 92.3 and 92.6% and 86.8 and 96.4%, respectively, was suitable for determining CDV involvement. Conjunctival swabs provide an alternative for distemper diagnosis, as there was a strong correlation between Ct values of conjunctival swabs and tissues ( r_s = -0.8498, p < 0.00001, n = 46). This information will aid in more efficient and accurate diagnoses in individuals, small-scale outbreaks, and epidemiologic investigations in wildlife.