1. Tuberculosis
Cecilia Calabrese

2. Definition
Tuberculosis is a chronic specific inflammatory infectious disease caused by Micobacterium tuberculosis in humans.
Usually affects the lungs but it can also affect any parts of the body.

3. Epidemiology
Tuberculosis is the most prevalent communicable infectious disease on earth and remains out of control in many developing nations
Roughly one of every three people on earth is infected by M.Tuberculosis. Disease, however, only occours in about 10% of case of infection, when the balance between host resistance and the pathogenecity of the bacteria tips in favour of the pathogenecity.

4. Currently, 95% of tuberculosis cases occur in developing countries where HIV/AIDS epidemics have had the greatest impact and where resources are often unavailable for proper identification and treatment of these diseases.
In many industrialized countries, most cases of tuberculosis occur in foreign-born.
The distribution is very uneven, with the highest incidences found in southern Asia and sub-saharan Africa
22 countries have 80% of TB cases today

5. Mycobacterium tuberculosis
In 1882, the microbiologist Robert Koch discovered the tubercle bacillus, at a time when one of every seven deaths in Europe was caused by TB. .

6. The agent: Mycobacteria sp.
TB is caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis)
M. tuberculosis and seven very closely related mycobacterial species (M. bovis, M. africanum, M. microti, M. caprae, M. pinnipedii, M. canetti and M. mungi) together comprise what is known as the M. tuberculosis complex.
M. tuberculosis, by far the commonest, is transmitted between humans through the airborne route.
M. bovis may penetrate the gastrointestinal mucosa or invade the lymphatic tissue of the oropharynx when ingested in milk from diseased cows.
Human infection with M. bovis has decreased significantly in developed countries as a result of the pasteurisation of milk and effective tuberculosis control amongst cattle.
Infection with the other organisms is relatively rare
Nontuberculous mycobacteria (NTM) are all the other mycobacteria which  do not cause tuberculosis but can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, or disseminated disease.

7. Mycobacterium – Bacterial caracteristics
strict aerobic,
nonmotile
non-spore-forming rod
it is an intracellular pathogen with interhuman transmission
the lipid richness of their cell wall gives the mycobacteria some particular characteristics:
- resistance to dehydration and chemical agents and therefore a long survival in outdoor environments
slow multiplication time
alcohol acid resistance (Ziel Nelhesen coloring)
most of the common antibiotics are ineffective
MT have a high complex lipid in their wall that readily binds with Ziel. Neelsen (Carbol fucsin) stain BUT subsequently resist decolorization by Acyd (Sulfuric Acid)

8. Transmission of TB
M. tuberculosis is carried in airborne particles, called droplet nuclei, of 1– 5 microns in diameter. Infectious droplet nuclei are generated when persons who have pulmonary or laryngeal TB disease cough, sneeze, shout, or sing.

9. Factors that Determine the Probability of M. tuberculosis Transmission
There are four factors that determine the probability of transmission of M. tuberculosis (Table 2.1).
The risk of developing active TB is greatest in patients with altered host cellular immunity, including extremes of age, malnutrition, cancer, immunosuppressive therapy, HIV infection, end-stage renal disease, and diabetes

11. Transmission of TB
Droplet nuclei containing tubercle bacilli are inhaled, enter the lungs.
Although the majority of inhaled bacilli are trapped in the upper airways and expelled by ciliated mucosal cells, a fraction (usually <10%) reach the alveoli

12. Alveolar macrophages that have not yet been activated phagocytize the bacilli through the bynding of the bacterial cell wall with a variety of macrophage cell-surface molecules
In the initial stage of host–bacterium interaction, 2 events may happen:
1) fusion between phagosomes and lysosomes preventing bacillary survival
2) After a phagosome forms, the survival of M. tuberculosis within it seems to depend on reduced acidification. The bacterial cell-wall may inhibit the intracellular increase of Ca2+. Thus, the Ca2+/calmodulin pathway, leading to phagosome–lysosome fusion, is impaired, and the bacilli may survive within the phagosomes. the bacilli begin to multiply, ultimately killing the macrophage.
After cell lysis , a variety of chemoattractants are released (e.g., complement components, bacterial molecules, and cytokines) that recruit additional immature monocyte-derived macrophages, including dendritic cells, which migrate to the draining lymph nodes and present mycobacterial antigens to T lymphocytes.

13. THE HOST RESPONSE
About 2–4 weeks after infection, two host responses to M. tuberculosis develop:
The Delayed -Type Hypersensitivity Reaction, a tissue-damaging response; it destroys unactivated macrophages that contain multiplying bacilli but also causes caseous necrosis of the involved tissues
The Cellular mediated Immunity (CMI) a T cell–mediated phenomenon resulting in the activation of macrophages that are capable of killing and digesting tubercle bacilli.
Although both of these responses can inhibit mycobacterial growth, it is the balance between the two that determines the form of tuberculosis that will develop subsequently.

14. THE DELAYED-TYPE HYPERSENSITIVITY REACTION
In a minority of cases, the macrophage-activating response is weak, and mycobacterial growth can be inhibited only by intensified DTH reactions, which destroys unactivated macrophages that contain multiplying bacilli leading to lung tissue destruction and causing caseous necrosis of the involved tissues
The result of the reaction is the formation of a caseous necrosis at the center of tuberculous granuloma surrounded by lymphocytes, macrophages, Langhans epithelioid cells.
The caseum is an unfavorable environment for the growth of mycobacteria due to the low oxygen tension.
The evolution of the caseous necrosis is variable, as it can undergo a fibrotic and calcifying transformation or it can undergo to colliquation that restore the optimal conditions for microbial growth due to the increase of oxygen tension .
The liquefied caseous material, containing large numbers of bacilli, can be drained through bronchi. and cavities are formed.Within the cavity, tubercle bacilli multiply, spill into the airways, and are discharged into the environment through expiratory maneuvers such as coughing and talking.

15. The Cellular mediated Immunity (CMI)
In the majority of infected individuals, the Cellular mediated Immunity (CMI) a T cell–mediated phenomenon resulting in the activation of macrophages that are capable of killing and digesting tubercle bacilli
Most of the bacilli are killed, but some survive within nonactivated macrophages, which carry them through lymphatic vessels to the regional lymph nodes
Control of Mycobacterium tuberculosis is mainly the result of productive teamwork between T-cell populations and macrophages (Mφ). M. tuberculosis survives within macrophages and dendritic cells (DCs) inside the phagosomal compartment. Gene products of MHC class II are loaded with mycobacterial peptides that are presented to CD4 T cells. CD8 T-cell stimulation requires loading of MHC I molecules by mycobacterial peptides in the cytosol,
The CD4 T-helper (Th) cells polarize into different subsets.
Th1 cells produce IL-2 for T-cell activation, interferon-γ (IFN-γ), or tumor necrosis factor (TNF) for macrophage activation.
Th17 cells, which activate polymorphonuclear granulocytes (PNGs), contribute to the early formation of protective immunity in the lung after vaccination..
CD8 T cells produce IFN-γ and TNF, which activate macrophages. They also act as cytolytic T lymphocytes (CTL) by secreting perforin and granulysin, which lyse host cells and directly attack M. tuberculosis. These effector T cells (Teff) are succeeded by memory T cells TM). TM cells produce multiple cytokines, notably IL2, IFN-γ, and TNF. During active containment in solid granuloma, M. Tuberculosis recesses into a dormant stage and is immune to attack. Exhaustion of T cells is mediated by interactions between T cells and DCs through members of the programmed death 1 system. Treg cells secrete IL10 and TGF-β, which suppress Th1. This process allows resuscitation of M. tuberculosis, which leads to granuloma caseation and active disease. B, B cell.
Macrophages process and present mycobacterial antigens in combination with MHC class II molecules to naive CD4 T cells that recognize through their TCR the complex Ag_MHCII.
CD4 T cells preferentially differenziate into Th1 cells that produce IL-2 for T-cell activation, interferon-γ (IFN-γ), or tumor necrosis factor (TNF) for macrophage activation.
TNF and IFN g act on macrophages, mobilize them and modify them into epithelioid cells. A few epithelioid cells get tranformed into multinucleated giant cell.
CD8 T-cell stimulation requires loading of MHC I molecules by mycobacterial peptides. CD8 T cells produce IFN-γ and TNF, which activate macrophages. They also act as cytolytic T lymphocytes (CTL) by secreting perforin and granulysin, which lyse host cells and directly attack M. tuberculosis. These effector T cells (Teff) are succeeded by memory T cells TM). TM cells produce multiple cytokines, notably IL2, IFN-γ, and TNF.

16. The Cellular mediated Immunity (CMI)
Furthermore, macrophages process and present mycobacterial antigens in combination with MHC class I molecules to CD 8 T cells that recognize through their TCR the complex Ag_MHCI.
CD8 T cells produce IFN-γ and TNF, which activate macrophages. They also act as cytolytic T lymphocytes (CTL) by secreting perforin and granulysin, which lyse host cells and directly attack M. tuberculosis. 
These effector T cells (Teff) are succeeded by memory T cells TM). TM cells produce multiple cytokines, notably IL2, IFN-γ, and TNF.
Most of the bacilli are killed, but some survive within nonactivated macrophages, which carry them through lymphatic vessels to the regional lymph nodes
Control of Mycobacterium tuberculosis is mainly the result of productive teamwork between T-cell populations and macrophages (Mφ). M. tuberculosis survives within macrophages and dendritic cells (DCs) inside the phagosomal compartment. Gene products of MHC class II are loaded with mycobacterial peptides that are presented to CD4 T cells. CD8 T-cell stimulation requires loading of MHC I molecules by mycobacterial peptides in the cytosol,
The CD4 T-helper (Th) cells polarize into different subsets.
Th1 cells produce IL-2 for T-cell activation, interferon-γ (IFN-γ), or tumor necrosis factor (TNF) for macrophage activation.
Th17 cells, which activate polymorphonuclear granulocytes (PNGs), contribute to the early formation of protective immunity in the lung after vaccination..
CD8 T cells produce IFN-γ and TNF, which activate macrophages. They also act as cytolytic T lymphocytes (CTL) by secreting perforin and granulysin, which lyse host cells and directly attack M. tuberculosis. These effector T cells (Teff) are succeeded by memory T cells TM). TM cells produce multiple cytokines, notably IL2, IFN-γ, and TNF. During active containment in solid granuloma, M. Tuberculosis recesses into a dormant stage and is immune to attack. Exhaustion of T cells is mediated by interactions between T cells and DCs through members of the programmed death 1 system. Treg cells secrete IL10 and TGF-β, which suppress Th1. This process allows resuscitation of M. tuberculosis, which leads to granuloma caseation and active disease. B, B cell.

17. Some lesions may heal by fibrosis with subsequent calcification
In the majority of infected individuals, the activated macrophages aggregate around the lesion’s center and effectively neutralize tubercle bacilli without causing further tissue destruction.
This response not only destroys macrophages but also produces early solid necrosis in the center of the tubercle, resembling soft cheese (caseous necrosis).
Although M. tuberculosis can survive, its growth is inhibited within this necrotic environment by low oxygen tension and low pH.
With the development of specific immunity, the accumulation at the site of the primary lesion of lymphocytes and large numbers of activated macrophages that evolve toward epithelioid and giant cells , lead to the granolomatous lesions (tubercles).
Some lesions may heal by fibrosis with subsequent calcification
granolomatous lesions (tubercles)

18. PRIMARY INFECTION
Typically, the inhaled bacilli implant in the distal airspaces of the lower part of the upper lobe or the upper part of the lower lobe, usually close to the pleura. As sensitization develops, a 1- to 1.5-cm area of gray-white inflammation with consolidation emerges, known as the Ghon Focus. In most cases, the center of this focus undergoes caseous necrosis. TBC bacilli within phagocytes, drain to the regional nodes, which also often caseate. This combination of parenchimal lung lesion and nodal involvement is referred to as the Ghon complex. The Ghon complex undergoes progressive fibrosis, often followed by radiologically detectable calcification (Ranke complex).
This is the Primary infection that usually occurs in the high endemic areas in children, otherwise in late adolescence and adulthood.
The clinical symptomatology is absent and the only signs of primary infection are radiological and biological (positivity of tuberculin tests between the fourth and sixth week of infection)

19. Pathogenesis
Most of the bacilli are killed, but some survive within nonactivated macrophages, which carry them through lymphatic vessels to the regional lymph nodes
Control of Mycobacterium tuberculosis is mainly the result of productive teamwork between T-cell populations and macrophages (Mφ). M. tuberculosis survives within macrophages and dendritic cells (DCs) inside the phagosomal compartment. Gene products of MHC class II are loaded with mycobacterial peptides that are presented to CD4 T cells. CD8 T-cell stimulation requires loading of MHC I molecules by mycobacterial peptides in the cytosol,
The CD4 T-helper (Th) cells polarize into different subsets.
Th1 cells produce IL-2 for T-cell activation, interferon-γ (IFN-γ), or tumor necrosis factor (TNF) for macrophage activation.
Th17 cells, which activate polymorphonuclear granulocytes (PNGs), contribute to the early formation of protective immunity in the lung after vaccination. Th2 cells and regulatory T cells (Treg) counter-regulate Th1-mediated protection via IL4, transforming growth factor β (TGF-β), or IL10.
CD8 T cells produce IFN-γ and TNF, which activate macrophages. They also act as cytolytic T lymphocytes (CTL) by secreting perforin and granulysin, which lyse host cells and directly attack M. tuberculosis. These effector T cells (Teff) are succeeded by memory T cells TM). TM cells produce multiple cytokines, notably IL2, IFN-γ, and TNF. During active containment in solid granuloma, M. Tuberculosis recesses into a dormant stage and is immune to attack. Exhaustion of T cells is mediated by interactions between T cells and DCs through members of the programmed death 1 system. Treg cells secrete IL10 and TGF-β, which suppress Th1. This process allows resuscitation of M. tuberculosis, which leads to granuloma caseation and active disease. B, B cell.
In contrast a differentitaion of naive CD4 cells toward Th2 cells and regulatory T cells (Treg) counter-regulate Th1-mediated protection, via IL4, transforming growth factor β (TGF-β), or IL10.
This process allows resuscitation of M. tuberculosis, which leads to granuloma caseation and active disease.

21. Clinical manifestations
1. LATENT INFECTION
2. PRIMARY TUBERCULOSIS
3. POST-PRIMARY TUBERCULOSIS

22. 1. Latent Tuberculosis Infection (LTBI)
LTBI is a condition in which M.tuberculosis survive in the body in a dormant state.
Persons with LTBI do not feel sick and do not have any symptoms.
They are also not contagious, and cannot spread the infection to others.
Chest X-ray is normal
LTBI may be detected by using the tuberculin skin test (TST) or an interferon-gamma release assay (IGRA).
Persons with LTBI do not have active tuberculosis but may develop it in the future. The risk of developing active TB is about 10%.
However, the risk is considerably higher for persons whose immune systems are weak, especially those with HIV co-infection.

23. Persons at increased risk
Persons at increased risk* for progression of infection to active tuberculosis include:
persons with human immunodeficiency virus (HIV) infection;
infants and children aged <5 years;
persons who are receiving immunosuppressive therapy such as tumor necrosis factor--alpha (TNF-α) antagonists, systemic corticosteroids equivalent to ≥15 mg of prednisone per day, or immune suppressive drug therapy following organ transplantation;
persons who were recently infected with M. tuberculosis (within the past 2 years);
persons with a history of untreated or inadequately treated active tuberculosis, including persons with fibrotic changes on chest radiograph consistent with prior active tuberculosis;
persons with silicosis, diabetes mellitus, chronic renal failure, leukemia, lymphoma, or cancer of the head, neck, or lung;
persons who have had a gastrectomy or jejunoileal bypass;
persons who weigh <90% of their ideal body weight;
cigarette smokers and persons who abuse drugs or alcohol; and
populations defined locally as having an increased incidence of active tuberculosis, possibly including medically underserved or low-income populations

24. 2. Primary Tuberculosis
Primary pulmonary tuberculosis occurs soon after the initial infection with Micobacterium tuberculosis.
In areas of high tuberculosis transmission, this form of disease is often seen in children or it can occurr in persons with impaired immunity (e.g., those with malnutrition or HIV infection),
Because most inspired air is distributed to the middle and lower lung zones, these areas of the lungs are most commonly involved in primary tuberculosis.
The initial lesion increases in size and can evolve in different ways. .

25. Pleural effusion, which is found in up to two-thirds of cases, results from the penetration of bacilli into the pleural space from an adjacent subpleural focus.

26. In severe cases, the primary site rapidly enlarges, its central portion undergoes necrosis, and cavitation develops (progressive primary tuberculosis).

27. Tuberculosis in young children is almost invariably accompanied by hilar or mediastinal lymphadenopathy caused by the spread of bacilli from the lung parenchyma through lymphatic vessels.
Enlarged lymph nodes may compress bronchi, causing obstruction and subsequent segmental or lobar collapse.
Partial obstruction may cause obstructive emphysema, and bronchiectasis may also develop.
Right-sided hilar lymphadenopathy and collapse-consolidation lesions of primary tuberculosis in a 4 yr old child.

28. Hematogenous dissemination, which is common and often asymptomatic, may result in the most severe manifestations of primary M. tuberculosis infection.
Bacilli reach the bloodstream and can disseminate into various organs, where they may produce granulomatous lesions.
Although healing frequently takes place, immunocompromised persons may develop miliary tuberculosis, tuberculous meningitis, or both.
Bilateral micronodular interstitial pattern indicative of miliary tuberculosis

29. Miliary or Disseminated Tuberculosis
Although it is often the consequence of primary infection in children, it may be caused by either recent infection or reactivation of old disseminated foci in adults.
The lesions are usually yellowish granulomas 1–2 mm in diameter that resemble millet seeds (thus the term miliary, coined by nineteenth-century pathologists).
The clinical manifestations are nonspecific:
Fever, night sweats, anorexia, weakness, and weight loss are presenting symptoms in the majority of cases. At times, patients have a cough and other respiratory symptoms caused by pulmonary involvement as well as abdominal symptoms.
Physical findings include hepatomegaly, splenomegaly, and lymphadenopathy.
Eye examination may reveal choroidal tubercles, which are pathognomonic of miliary tuberculosis, in up to 30% of cases.
Meningismus occurs in <10% of cases

30. 3. Postprimary Tuberculosis
Also called adult-type, reactivation, or secondary tuberculosis,
Postprimary disease results from endogenous reactivation of latent infection
It is usually localized to the apical and posterior segments of the upper lobes, where the substantially higher mean oxygen tension favors mycobacterial growth. In addition, the superior segments of the lower lobes are frequently involved.

31. The extent of lung parenchymal involvement varies greatly, from small infiltrates to extensive cavitary disease.
With cavity formation, liquefied necrotic contents are ultimately discharged into the airways, resulting in satellite lesions within the lungs that may in turn undergo cavitation

32. Massive involvement of pulmonary segments or lobes, with coalescence of lesions, produces tuberculous pneumonia.
Although up to one-third of untreated patients reportedly succumb to severe pulmonary tuberculosis within a few weeks or months after onset (the classical “galloping consumption” of the past),
others undergo a process of spontaneous remission or proceed along a chronic, progressively debilitating course (“consumption”).
Under these circumstances, some pulmonary lesions become fibrotic and may later calcify, but cavities persist in other parts of the lungs. Individuals with such chronic disease continue to discharge tubercle bacilli into the environment

33. Diagnosis of TBC
Symptoms
Microbiology
Radiology
Response to treatment

34. 1. SYMPTOMS
The key to the diagnosis of tuberculosis is a high index of suspicion. Symptoms and signs are often nonspecific and insidious, consisting mainly of
Systemic symptoms
Weight loss
Loss of appetite
Night sweats
Fever, often low-grade and intermittent, in up to 80% of cases and wasting. (Absence of fever, however, does not exclude tuberculosis)
Respiratory symptoms
Coughing
Purulent sputum, sometimes with blood streaking
Massive hemoptysis may ensue as a consequence of the erosion of a blood vessel in the wall of a cavity, or from rupture of a dilated vessel in a cavity (Rasmussen’s aneurysm) or from aspergilloma formation in an old cavity.

35. 2. MICROBIOLOGY
For patients with suspected pulmonary tuberculosis, three sputum specimens, preferably collected early in the morning, should be submitted to the laboratory for AFB smear and mycobacterial culture
ACID-FAST BACILLI MICROSCOPY has relatively low sensitivity (40–60%) in confirmed cases of pulmonary tuberculosis
MYCOBACTERIAL CULTURE Definitive diagnosis depends on the isolation and identification of M. tuberculosis from a clinical specimen.
Specimens may be inoculated onto egg- or agar-based medium (e.g., Lowenstein-Jensen or Middlebrook 7H10) and incubated at 37°C (under 5% CO2 for Middlebrook medium). Because most species of mycobacteria, including M. tuberculosis, grow slowly, 4–8 weeks may be required before growth is detected. A variety of biochemical tests have traditionally been used to speciate mycobacterial isolates

36. MYCOBACTERIAL NUCLEIC ACID AMPLIFICATION
MYCOBACTERIAL NUCLEIC ACID AMPLIFICATION. These systems permit the diagnosis of tuberculosis in as little as several hours. High costs.
DRUG SUSCEPTIBILITY TESTING the initial isolate of M. tuberculosis should be tested for susceptibility to isoniazid, rifampin, and ethambutol.
In addition, expanded susceptibility testing is mandatory when resistance to one or more of these drugs is found or the patient either fails to respond to initial therapy or has a relapse after the completion of treatment.

37. 3. RADIOGRAPHIC PROCEDURES
Chest radiograph in the typical cases show upper-lobe infiltrates with cavitation.
In contrast, immunosuppressed patients, including those with HIV infection, may have “atypical” findings on chest radiography (e.g., lower-zone infiltrates without cavity formation).
CT scan may be useful in interpreting questionable findings on plain chest radiography

43. DIAGNOSIS OF LATENT M. TUBERCULOSIS INFECTION
1. Tuberculin Skin Testing (Mantoux skin test (PPD)
0.1 ml of PPD (a purified protein derivative of tuberculin) equal to 5U is injected into the forearm just under the skin.
a health professional should read the test 48 to 72 hours after it is administered to check for a reaction.
if there is a reaction (swelling -papula ), an X-ray or sputum sample is needed to confirm active disease that occurs only in 10%. of people who test positive for TB infection

44. False positive reactions may be caused by infections with nontuberculous mycobacteria and by bacille Calmette- Guerin (BCG) vaccination
HIV can also produce a false negative reading on the Mantoux skin test

45. DIAGNOSIS OF LATENT M. TUBERCULOSIS INFECTION
2. IFN-γ Release Assays (IGRAs)
Two in vitro assays that measure T cell release of IFN-γ in response to stimulation with the highly tuberculosis-specific antigens ESAT-6 and CFP-10 are available:
QuantiFERON-TB Gold® (Cellestis Ltd., Carnegie, Australia) is a wholeblood enzyme-linked immunosorbent assay (ELISA) for measurement of IFN-
T-SPOT.TB® (Oxford Immunotec, Oxford, UK) is an enzyme-linked immunospot (ELISpot) assay.
IGRAs are more specific than the TST as a result of less cross-reactivity because of BCG vaccination and sensitization by nontuberculous mycobacteria.

46. THERAPY
The treatment regimen of choice for virtually all forms of tuberculosis in both adults and children consists of a 2-month initial phase of isoniazid, rifampin, pyrazinamide, and ethambutol followed by a 4-month continuation phase of isoniazid and rifampin. Treatment may be given daily throughout the course or intermittently three times weekly,.

47. MONITORING THE RESPONSE TO TREATMENT
Bacteriologic evaluation of sputum is the preferred method of monitoring the response to treatment for tuberculosis.
Patients with pulmonary disease should have their sputum examined monthly until cultures become negative.
With the recommended regimen, >80% of patients will have negative sputum cultures at the end of the second month of treatment.
By the end of the third month, virtually all patients should be culture negative