TUBERCULOSIS [ Symptoms and signs / Cause / Pathogenesis / Primary Tuberculosis / Reactivation Disease / Risk factors / Complication] 


       In 2018 ,an estimated people 10 million people fell ill with tuberculosis [TB] worldwide . A total of 1.5 million people died from TB in 2018 . worldwide , TB is one of the top 10 cause of death and the leading cause from a single infectious agent . tuberculosis generally affects the lungs, but can also affect other parts of the body . about 25 % of TB patients of the world are Indians . in India , each year , approx. 220,000 deaths an reported due to tuberculosis.


Pulmonary Tuberculosis

    Symptoms and Signs

       *Cough up sputum

       *Cough up blood

       *Consistent low- grade fever

       *Night sweats

       *Chest pains

       *Unexplained weight loss


Causes

       Pulmonary TB is caused by the bacterium mycobacterium tuberculosis. TB is contagious . This means the bacteria is easily spread from an infected person to someone else. You can get TB by breathing in air droplets from a cough [or] sneeze of an infected person. The resulting lung infection is called primary

Pathogenesis

  The characteristic pathologic changes depend on the type of infection :

  *Primary pulmonary TB[primary exposure]

          It is characterized by the Ghon complex, which is consist of

             1]Subpleural focus of tuberculosis inflammation

             2]Infected [inflamed] lymph nodes draining the primary subpleural lesion.

   *Second pulmonary TB [reactivation]

               Is characterized by a focus of infection and granuloma formation usually in the apex of the lung. The small granulomas [tubercles] eventually coalesce to form larger areas of consolidation with central caseating necrosis . regional lymph nodes contain caseating granulomas. 

   *Progressive pulmonary TB

               Primary or secondary TB may go on to heal as caseating granulomas are replaced by fibrosis and calcification. However, if the case does not heal spontaneously or with therapy, the disease progress to form cavities or spread to other parts of the lung and other organs of the body through lymphatic channels and the blood stream. 

Primary Tuberculosis

         The tuberculosis bacilli establish infection in the lungs after they are carried in droplets small enough [5 to10 microns] to reach the alveolar spaces. If the defense system of the host fails to eliminate the infections, the bacilli proliferate inside alveolar macrophages and eventually kill the cells. The infected macrophages produce cytokines and chemokines that attract other phagocytic cells, including monocytes, other alveolar macrophages and neutrophils, which eventually form a nodular granulomatous structure called the tubercle . if the bacterial replication is not controlled, the tubercle enlarges and the bacilli enter local draining lymph nodes. This leads to lymphadenopathy, a characteristic clinical manifestation of primary tuberculosis. The lesion produced by the expansion of the tubercle into the lung parenchyma and lymph nodes involvement is called the ghon complex.



 

           Unchecked bacterial growth may lead to haematogenous spread of bacilli to produce disseminated TB in various vital organs of the body. Disseminated disease with lesions resembling millet seeds is termed millet seeds is termed miliary TB. In the absence of treatment, death ensures in 80% of cases. The remaining patients develop chronic disease [or] recover. chronic disease is characterized by repeated episodes of  heating by fibrotic changes around the lesions and tissue breakdown. Complete spontaneous eradication of the bacilli is rare.


 

  Reactivation Disease          

              Reactivation TB results from proliferation of a previously dormant bacterium seeded at the time of the primary infection. Among individuals with latent infection and no underlying medical problems,  reactivation disease occurs in 5 to 10 per cent. it is not clear what specific host factors maintain the infection in a latent state and what triggers the latent infection to become overt. The disease process in reactivation TB tends to be localized  [in contrast to primary disease]. There is little regional lymph node involvement and less caseation. The lesion typically occurs at the lung apices, and disseminated disease is unusual unless the host is severely immunosuppressed. It is generally believed that successfully contained latent TB confers protection against subsequent TB  exposure. In many people, the infection waxes and wanes. Tissue destruction and necrosis are often balanced by healing and fibrosis. Affected tissue is replaced by scarring and cavities filled with caseous necrotic material. During active disease, some of these cavities are joined to the bronchi and this material can be coughed up. The sputum  contains living bacteria, and thus can spread the infection .


 

   

    Risk factors;    

       *Contact with a patient of TB

       *Live in  crowded or unclean living conditions

       *Have poor nutrition 


 Complications

      *Hemoptysis                                            *Bronchiectasis

      *Pleurisy                                                  *Laryngitis

      *Pleural effusion                                      *Pneumothorax

      *Cor-pulmonale[congestive heart failure]

      *Empyema