Post-mortem examination and laboratory-based analysis for the diagnosis of bovine tuberculosis among dairy cattle in Ecuador

Abstract

a b s t r a c tVeterinary inspection in slaughterhouses allows for the detection of macroscopic lesions reminiscent of bovine tuberculosis, but the presence of Mycobacterium bovis must be confirmed by laboratory methods. This study aimed at comparing the performances of the standard diagnostic tools used to identify M. bovis in tissue specimens sampled from suspicious animals. During a two years period, 1390 cattle were inspected at the Machachi abattoir in the Mejia canton -Ecuador. A total of 33 animals with granulomatous lesions were detected, representing 2.33% (16/687) and 2.42% (17/703) animals examined in 2007 and 2008, respectively. Ninety-four tissue specimens were sampled and screened for the presence of mycobacteria. Acid-fast bacilli were identified in one third of the suspicious cattle (11/33) and suggestive microscopic lesions in 27.3% (9/33) of the samples examined by direct microscopy and histopathology, respectively. Culturing on Stonebrink medium and 16S-rRNA-based polymerase chain reaction (PCR) yielded 36.4% (12/33) and 27.3% (9/33) of positives, respectively. Compared to culture, other diagnostic procedures displayed a lower sensitivity, with 56.5% for PCR, and 43.5% for direct microscopy and histopathology; however, the specificity was higher (94.4% for PCR and microscopy, and 97.2% for histopathology). We conclude that reliable post-mortem laboratory testing either requires the combination of a set of available diagnostic tools or necessitates the development of improved new-generation tools with better sensitivity and specificity characteristics.

Estimation of Sensitivity and Specificity of Bacteriology, Histopathology and PCR for the Confirmatory Diagnosis of Bovine Tuberculosis Using Latent Class Analysis

“…In Taylor et al [22], comparison of RD4 PCR and IS 1081 PCR with the gold standard of bacteriology showed a sensitivity of approximately 50% and 70% respectively. Thacker et al [23] reported that out of 30 M. bovis culture positive tissues, only 20 were positive using IS 6110 real-time PCR and in Proaño-Perez et al [24], eight animals were found PCR positive over the twelve positive in bacteriology. Only Cardoso et al [25] reported a frequency of PCR-positive results similar to that of culture-positive results (51.5% versus 54.5%) over 35 lymph nodes samples from animals with macroscopic lesions consistent with M. bovis infection.…”

Situation of bovine tuberculosis in Ecuador

“…Vigilance is recommended, however, since not all infected cattle exhibit gross lesions. On the other hand, detailed meat inspection allows the identification of lesions in apparently healthy animals, which increases the number of detected animals and avoids the consumption of BTB-infected cattle (40).…”

Bovine Tuberculosis in the Republic of Macedonia: Postmortem, Microbiological and Molecular Study in Slaughtered Reactor Cattle

“…However, being unable to identify 100% of infected animals, this method cannot be considered as such even in samples with bTB lesions. The sensitivity of the method varies depending of different factors such as sampling procedure, type of samples, sample storage and implemented bacteriology protocols (type of decontamination, culture media) (13) and ranges from 4.7% to 85% (12,33,34,35,36,37).…”