TUBERCULOSIS: CAUSATIVE AGENT, MODE OF TRANSMISSION, TYPES, PATHOGENESIS, TREATMENT AND MCQs

INTRODUCTION:-

1.) Factors contributing to higher incidence of tuberculosis are malnutrition, inadequate medical care, Poverty, crowding, uncontrolled diabetes, alcoholism and happen in immunocompromised states.

2.) HIV – infected individuals have very high incidence of tuberculosis all over the world.

CAUSATIVE AGENT:- Caused by Mycobacterium tuberculosis also called as Tubercle bacillus or Koch’s bacillus.

1.) This organism is an strict aerobe and thrives best in tissues with high oxygen tension such as in the Apex of lungs.

2.) M. tuberculosis is an acid – fast bacteria ( not easily decolourized by acid when stained ).

MODE OF TRANSMISSION:-

Humans acquire infection from tubercle bacilli by following ways :-

1.) By inhalation of organism from the fresh cough droplets.

2.) By the injection of organism as it leads to development of tonsillar or intestinal tuberculosis.

3.) By the inoculation of the organism into the skin.

4.) By trans-placental route which results into the development of the congenital tuberculosis in foetus from infected mother.

SPREAD OF TUBERCULOSIS:-

1.) Local spread :- This takes place by bacilli macrophages carrying bacilli into the surrounding tissue.

2.) Lymphatic spread :- Tuberculosis is primarily an infection of lymphoid tissue. The bacilli may pass into the lymphoid follicles of pharynx, bronchi, intestine or regional lymph node resulting in regional tuberculosis lymphadenitis.

3.) Haematogenous spread :- This occur as a result of tuberculous bacillaemia because of the drainage of lymphatics into the venous system or due to the caseous material escaping through ulcerated walls of vein.

4.) By natural passage :- like lung lesions into pleura, renal lesions, infected sputum into larynx etc.

PATHOGENESIS :-

1.) Mycobacterium are aerobic, non – Spore forming, non-motile bacilli with a waxy coat that causes them to retain the red dye.

2.) There are three important consideration in the pathogenesis of tuberculosis :-

a.] the basis of virulence of the organism.

b.] the relationship of hypersensitivity to immunity against infection.

c.] the pathogenesis of tissue destruction and caseous necrosis ( the death of most or all cells of the cells in an organ or tissue due to disease, injury or failure of blood supply ).

3.) Hypersensitivity and immunity are closely related and are initiated through CD4+T lymphocytes sensitized against specific antigen in tuberculin.

4.) The development of cell – mediated, or type 4 hypersensitivity to the tuberculin bacillus probably explains the organism’s destructiveness in tissue.

TYPES OF TUBERCULOSIS :-

A.] PRIMARY TUBERCULOSIS :- The infection of an individual who has not been previously infected or immunized is called primary tuberculosis or Ghon’s complex or childhood tuberculosis. It mostly occurs in children. In this almost whole of the lung is affected. Ghon’s complex ( lungs lesions as consolidation lymphatic vessel and hilar lymph node lesions) where formed. The fate of primary tuberculosis is healing by fibrosis, calcification and may get reactivated in weakened immunity.

B.] SECONDARY TUBERCULOSIS :- The infection of an individual who has been previously infected of sensitized is called secondary, or post primary or reinfection, or chronic tuberculosis. It occurs in children and adults. In this lungs, lymph nodes lesions, cavitation ( formation of cavity ), fibrocaseous lesions, caseous pneumonia, pleurisy/effusion occur. The fate of secondary tuberculosis is consolidation, parenchymal nodules, thickened pleura, amyloidosis, reactivation of healed lesions in impaired immunity and AIDS.

DIAGNOSIS AND TREATMENT :- TB can be diagnosed by radiographic procedure like chest X – Rays, by taking sample of sputum, by skin test, by fine Needle aspiration cytology etc. TB can be treated by antibiotics.

Treatment:

First Line Drugs for Treatment

  • Isoniazide
  • Streptomycin
  • Pyrazinamide
  • Rifampicin
  • Ethambutol

In India Treatment is available under DOTS programme run by Gov of India

QUESTIONS….

Ques:1] How does tuberculosis spread ?

a.) Through air

b.) Through sexual contact

c.) Through contaminated food

d.) Through blood

e.) Both (a) and (c)

Ques:2] What make TB hard to diagnose ?

a.) Symptoms aren’t always obvious

b.) Symptoms come and go

c.) The disease may take years to become active

d.) Both (a) and (b)

Ques:3] What are the symptoms of active TB ?

a.) Weight loss

b.) Night sweats

c.) Loss of appetite

d.) All of the above

Ques:4] How is TB diagnosed ?

a.) Chest X – Ray

b.) Sample of sputum

c.) Skin test

d.) All of the above

Ques:5] How is TB treated ?

a.) Antiviral medicines

b.) Antibiotics

c.) Surgery

d.) Chemotherapy

Ques:6] What is causing TB to become a serious public health problem ?

a.) A rise in number of people with HIV infection

b.) An increasing number of immigrants from areas of the world where TB is common

c.) An increasing number of homeless people

d.) More people failing to finish their TB treatment

e.) All of the above

Ques:7] Who is at risk of developing tuberculosis in any country ?

a.) People taking certain medicines

b.) Migrant farm workers

c.) People with HIV

d.) All of the above

Ques:8] Tuberculosis is caused by which microorganism ?

a.) Mycobacterium leprae

b.) Mycobacterium tuberculosis

c.) Mycobacterium avium

d.) None of the above

Ques:9] Does tuberculosis only affect the lungs ?

a.) True

b.) False

Ques:10] What are the symptoms of the people suffering from latent tuberculosis ?

a.) No symptoms

b.) Patient feel sick

c.) Spread TB bacteria to others

d.) Patient have negative TB blood test

 

SOLUTION….

Sol.1] (a) Through air

Sol.2] (c) The disease may take years to become active

Sol.3] (d)

Sol.4] (d)

Sol.5] (b) Antibiotics

Sol.6] (e)

Sol.7] (d)

Sol.8] (b) Mycobacterium tuberculosis

Sol.9] (b)

Sol.10] (a) No symptoms

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REFERENCE :-

1.) Robbin’s basic pathology.

2.) Textbook of pathology by Harsh Mohan.

 

 

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