**1. Introduction**

Tuberculosis caused by *M*. *tuberculosis* is the leading cause of human deaths from single infectious agent and fall in the top 10 causes of deaths worldwide. More than 10 million people suffered from TB in 2016 and the global case fatality and incident rates were 16% and 140/100,000 [1]. radiography, and volatile organic compound determination can detect active tuberculosis. The latter group of procedures is assisted by the appearance of clinical symptoms. As the form of mycobacterial detection differs among these methods, sensitivity, and time frame to

Paralleling of Diagnostic Endeavor for Control of Mycobacterial Infections and Tuberculosis

http://dx.doi.org/10.5772/intechopen.77316

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Whole blood sample can be used to diagnose both mycobacterial infections and tuberculosis based on the host immune response. Characteristics of blood parameters such as interferon-induced genes, myeloid genes, inflammatory genes and B and T-cells regulation genes, and proteomic profiles are used as markers in the detection of mycobacterial infections and tuberculosis [9].

IGRAs are immune cell-mediated in vitro blood tests that measure mononuclear cell (lymphocytes: T and B cells) release of interferon-γ (INF-γ) after stimulation by antigens specific for Mycobacterium. Following infection, the body immune response is triggered and immune cells such as macrophages, T-cells, B-cells, and natural killer cell are involved. Macrophages, which form the first defense line, engulf, kill, and eliminate *Mycobacteria tuberculosis*. Some *M*. *tuberculosis* escapes the immune mechanism and survives and replicate in macrophages. T-cells, especially CD4 and CD8 T-cells, produce cytokine—interferon-gamma, which in turn activate infected macrophages to produce reactive nitric oxide and related reactive nitrogen intermediates to kill the *M*. *tuberculosis* and eliminate it through the actions of phagosomes and lysosomes [10]. The lymphocytes can produce interferon-gamma in vitro whenever stimulated by *M*. *tuberculosis* antigen. This feature is used to assist in the diagnosis of *Mycobacteria tuberculosis* infection. Principally, the lymphocytes of a person infected with *M*. *tuberculosis* release interferon-gamma when mixed with *M*. *tuberculosis* derived antigens. There are two enzyme-linked assays; enzyme-linked immunosorbent assay (ELISA), and enzyme-linked immunosorbent spot (ELISPOT) assay. The assays detect INF-γ release by lymphocytes of sample donor following exposure to antigens found on the *M*. *tuberculosis* complex (MTBC). In ELISA based IGRA, fresh whole test blood sample is mixed with *M. tuberculosis* antigens and control. The antigen is made up of 6kDaA early secreted antigen target (ESAT-6), 10-kDa culture filtrate protein (CFP-10), and TB7.7 [11]. Normal saline is used as a control. The assay gives the concentration of INF-γ in international units per milliliter (IU/ml). The test result is considered positive when the difference in INF-γ response to the TB antigen between the test

diagnosis vary as well. Nevertheless, the goal remains to end TB by 2035 [7].

antigen value and the control value is greater than the cut-off of 0.35 IU [12].

Principally, the ELISPOT assay works on peripheral blood mononuclear cells (PBMCs) from a whole blood sample. The PBMCs are mixed with synthetic peptide antigens (ESAT-6 and CFP-10) and the control and incubated to stimulate interferon-γ secretion by the cells. Secreted interferon-γ is captured by specific antibodies and accumulated as spots. Thus, ELISPOT assay gives the number of interferon-γ producing cells (spots). The test result is

**2. Blood tests in TB diagnosis**

**2.1. Interferon-γ release assays (IGRAs)**

Inhalation of *M*. *tuberculosis* stimulates host cellular immune response with a consequence of either clearance of the organism or infection. Infection may result into latent mycobacteria infection (LTBI) (no clinical evidence) [2] or active tuberculosis (pulmonary or extra-pulmonary) [1].

The global LTBI prevalence is 23%, which is approximately 1.7 billion of the population [3]. About 5–15% of LTBI may progress to active TB [4]. LTBI is currently diagnosed by tuberculin skin test (TST) or gamma-interferon release assays (IGRA) [5]. On average the prevalence of active TB globally is 0.14% and the figures may vary according to regions [1].

The zoonotic potential of *M. bovis* constitutes a public health concern. Ingestion of *M. bovis* contaminated material is reported to be a primary cause of infection in humans and the resulting TB may take both pulmonary and extra-pulmonary form [6]. The burden of tuberculosis in humans due to *M. bovis* is variable in different countries, ranging from 5 to 28% with mortalities of 8.7% [6]. Therefore, this pathogen should be given due weight in TB diagnosis and consequently control plan.

According to WHO report, 53 million deaths have been averted from 2000 to 2016 following diagnosis and treatment. There is a big gap between diagnosis and treatment otherwise the number of deaths prevented could be even higher [1]. Every year the health systems fail to capture 3 million TB patients [7] some of them may be due to the nature of mycobacteria and diagnostic setup [6].

When prevention of pathogen-host contact is inadequate, early, rapid, and discriminative diagnosis become the primary factor for treatment success and reduction of further transmissions. Inappropriate diagnosis of symptomatic patients with active TB, LTBI, or other confounding diseases, for example, sarcoidosis, usually lead to delayed or wrong administration of full TB treatment or prophylactic dose [8]. This chapter, therefore, focuses on mycobacterial infections and tuberculosis diagnosis by assessing and comparing different procedures so as to suggest a best diagnostic method(s) and research direction.

The assessment and comparison of diagnostic procedures in this chapter are based on either single or combination of features such as the type of sample tested, pathological, or morphological changes or immunological reactions. Some of the known mycobacterial infections and tuberculosis diagnostic sample sources include sputum for smear, sniffing, and culture, blood for biomarkers such as interferon, inflammatory cells, proteins and transcriptomes, urine, and breath for volatile organic compounds (VOCs). Moreover, anatomical and physiological changes in tissues can allow diagnosis of tuberculosis through imaging techniques and skin reaction. Among these procedures, IGRA, TST and transcriptomic studies can detect mycobacterial infections while smear microscopy, culture and sniffing results of sputum, radiography, and volatile organic compound determination can detect active tuberculosis. The latter group of procedures is assisted by the appearance of clinical symptoms. As the form of mycobacterial detection differs among these methods, sensitivity, and time frame to diagnosis vary as well. Nevertheless, the goal remains to end TB by 2035 [7].
