Diagnosis of tuberculosis: Available technologies, limitations, and possibilities

Abstract

Rapid diagnosis and treatment are important for preventing transmission of Mycobacterium tuberculosis. However, the diagnosis of tuberculosis continues to pose serious problems, mainly because of difficulties in differentiating between patients with active tuberculosis and those with healed lesions, normal mycobacterium boris BCG (Bacillus Calmette Guerin) vaccinated individuals, and unvaccinated Manteux positives. Physicians still rely on conventional methods such as Ziehl-Neelsen (ZN) staining, fluorochrome staining, sputum culture, gastric lavage, and other non-traditional methods. Although the tuberculin test has aided in the diagnosis of tuberculosis for more than 85 years, its interpretation is difficult because sensitization with nontuberculous mycobacteria leads to false-positive tests. There have been numerous unsuccessful attempts to develop clinically useful serodiagnostic kits for tuberculosis. A number of proteinaceous and nonprotein antigens (such as acyltrehaloses and phenolglycolipids) have been explored from time to time for the development of such assays but they have not proved to be clinically useful. It has been difficult to develop an ELISA utilizing a suitable antigen because M. tuberculosis shares a large number of antigenic proteins with other microorganisms that may or may not be pathogenic. With the advent of molecular biology techniques, there have been significant advances in nucleic acid-based amplification and hybridization, which are helping to rectify existing flaws in the diagnosis of tuberculosis. The detection of mycobacterial DNA in clinical samples by polymerase chain reaction (PCR) is a promising approach for the rapid diagnosis of tuberculous infection. However, the PCR results must be corrected for the presence of inhibitors as well as for DNA contamination. In the modern era of genetics, marked by proteomics and genomics, the day is not far off when DNA chip-based hybridization assays will instantly reveal mycobacterial infections.

Tuberculosis in Elephants: Antibody Responses to Defined Antigens of Mycobacterium tuberculosis , Potential for Early Diagnosis, and Monitoring of Treatment

“…Since the estimation is based on the results of trunk wash culture and this method has inadequate sensitivity, the true number of elephants harboring TB is likely higher. In humans, TB diagnosis is based on evaluation of clinical symptoms and laboratory methods, such as chest X-ray, smear microscopy, culture, or PCR probes (7,29). In cattle, the intradermal skin test remains the primary screening tool in most countries, while the in vitro whole-blood gamma interferon Bovigam assay (Prionics AG, Schlieren, Switzerland) is generally used as an ancillary test (28).…”

Analysis of the Shotgun Expression Library of the Mycobacterium tuberculosis Genome for Immunodominant Polypeptides: Potential Use in Serodiagnosis

“…In addition, the procedures involved should be simple, not capital intensive, and environmentally friendly and should have a low cost per test, particularly for developing countries. A number of attempts (6,7,9,22,23,25,29,36,37,39) select antigens relevant for serodiagnosis, but none of them have been reported to be promising (10). Three antigens of M. tuberculosis, viz., Mtb11, Mtb8, and Mtb48, produced as a genetically fused polyprotein were tested together with the previously reported 38-kDa protein in an ELISA to detect antibodies in TB patients.…”

“…Because of low-sensitivity (direct staining of acid-fast bacilli) and time-consuming (culture) diagnostic techniques, a fast etiological confirmation is essential for further management of patients. In this context, approaches based on serological diagnosis have been developed in the past (6,7,9,22,23,25,29,36,37,39), but differentiation of patients with active disease from Mycobacterium bovis BCG-vaccinated individuals or those with Mantoux-positive testing and clinical signs of disease still remains a major problem (10,30). The efforts to explore candidate antigens have received a great boost with the complete sequencing of the Mycobacterium tuberculosis H37Rv genome, comprising 4,411,529 bp with 3,924 open reading frames (ORFs), accounting for ϳ91% of the potential coding capacity.…”

Enhancement of Diagnostic Efficiency by a Gamma Interferon Release Assay for Pulmonary Tuberculosis

“…However, its sensitivity is only 40 to 60% under field conditions, 50% in paucibacillary subjects, and 35 to 70% in children and adults with extrapulmonary TB (7,10,14). Limitations of these traditional microbiological methods have led to the development of additional methods, such as the gamma interferon (IFN-␥) release assay, as an aid in clinical and laboratory investigations of cases of human TB.…”