Review on Bovine Tuberculosis: An Emerging Disease Associated with Multidrug-Resistant Mycobacterium Species

Abstract

Bovine tuberculosis is a serious infectious disease affecting a wide range of domesticated and wild animals, representing a worldwide economic and public health burden. The disease is caused by Mycobacteriumbovis and infrequently by other pathogenic mycobacteria. The problem of bovine tuberculosis is complicated when the infection is associated with multidrug and extensively drug resistant M. bovis. Many techniques are used for early diagnosis of bovine tuberculosis, either being antemortem or postmortem, each with its diagnostic merits as well as limitations. Antemortem techniques depend either on cellular or on humoral immune responses, while postmortem diagnosis depends on adequate visual inspection, palpation, and subsequent diagnostic procedures such as bacterial isolation, characteristic histopathology, and PCR to reach the final diagnosis. Recently, sequencing and bioinformatics tools have gained increasing importance for the diagnosis of bovine tuberculosis, including, but not limited to typing, detection of mutations, phylogenetic analysis, molecular epidemiology, and interactions occurring within the causative mycobacteria. Consequently, the current review includes consideration of bovine tuberculosis as a disease, conventional and recent diagnostic methods, and the emergence of MDR-Mycobacterium species.

High Specificity Test Algorithm for Bovine Tuberculosis Diagnosis in African Buffalo (<em>Syncerus caffe</em>r) Herds

“…These parameters are often considered constant across different populations [4]. However, sensitivity and specificity may be influenced by various factors, including infection stage and disease severity, and exposure to environmental mycobacteria [2,4]. Furthermore, the infection status of the herd is an important consideration for the optimal application of a diagnostic assay or algorithms.…”

“…African buffaloes (Syncerus caffer) are important maintenance hosts of bovine tuberculosis (bTB) in South Africa [1]. The causative agent of bTB in buffaloes is Mycobacterium bovis, a pathogenic member of the Mycobacterium tuberculosis complex (MTBC) [2]. Control measures in South Africa require mandatory screening for M. bovis infection prior to movement of buffaloes [1].…”

“…However, with an inverse relationship between sensitivity and specificity for an imperfect test, increasing test sensitivity results in compromised specificity, and vice versa [4]. Various factors influence bTB test sensitivity and specificity when using methods based on immune responses, including the test antigens selected for the assay, exposure of the host to environmental mycobacteria, and the specific host biomarkers measured in cytokine release assays (CRA) [2,4].…”

“…Ante-mortem diagnosis of M. bovis infection in buffaloes relies on the measurement of antigen-specific cell-mediated host immune responses [2,5]. These include the single comparative intradermal tuberculin test (SCITT), QuantiFERON ® -TB Gold Plus (QFT) or Bovigam ® interferon-gamma (IFN-γ) release assays (IGRA) and QFT IFN-γ inducible protein 10 release assay (IPRA) [6].…”

“…The SCITT and Bovigam ® IGRA measure host responses to purified protein derivatives (PPD), which are antigens consisting of a crude mixture of proteins, carbohydrates and lipids obtained from M. bovis (bovine PPD), M. avium (avian PPD), and in some cases from M. fortuitum (fortuitum PPD) [2,4,10]. Assays using PPDs typically have high sensitivity due to the greater number of antigens used to stimulate a detectable immune response, but often have compromised specificity due to cross-reactive responses to environmental mycobacteria that share antigens with MTBC [2,5,11]. The inclusion of avian PPD to these tests has led to increased specificity by accounting for sensitisation to M. avium and closely related nontuberculous mycobacterial (NTM) species [12].…”