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Chapter: Microbiology and Immunology: Bacteriology: Mycobacterium tuberculosis

Prevention and Control for Mycobacterium tuberculosis Infections

These include chemoprophylaxis, vaccination, and general health measures.

Prevention and Control

These include chemoprophylaxis, vaccination, and general health measures.

 Chemoprophylaxis

Chemoprophylaxis or preventive chemotherapy is carried out by use of antitubercular drugs, such as INH. INH is usually used for treatment of:

·           Persons with latent tuberculosis,

·           Patients with HIV infection,

·           Recent contact of patients with contagious tuberculosis in past 3 months, even if TST result is negative,

·           Unvaccinated children, and

·           Elderly person with radiological evidence of quiescent disease.

      These cases are treated by INH, given in a dose of 5 mg/kg daily for 6–12 months. Results of the study have shown that chemoprophylaxis by INH has considerably reduced the risk of acquiring the disease nearly by 90%.

 Vaccination

Vaccination against tuberculosis is carried out by admin-istration of the vaccine. BCG is a live attenuated vaccine prepared from attenuated strain of M. bovis. This attenu-ated strain was originally prepared by Calmette and Guerin (1921). They subcultured the bacterium every 3 weeks for 230 subcultures on potato soaked in sterile bile con-taining 5% glycerol during a period of 13 years. The BCG vaccine is available in liquid as well as freeze-dried (lyoph-ilized) form. The lyophilized form is commonly used,which is reconstituted with sterile physiological saline to make a final concentration of 0.1 mL before admin-istration. The reconstituted vaccine has a shelf life of 3–6 hours. The vaccine is given by the administration of 0.1 mL of reconstituted vaccine intradermally.

      In a positive test, small nodule develops at the site of inoc-ulation 2–3 weeks after injection. It increases slowly in size and by about 5 weeks, it attains a diameter of 4–8 mm. It then subsides or breaks into a shallow ulcer, which heals by scarring.

      Following BCG vaccination, a tuberculin-negative indi-vidual is converted into a positive reactor. The immu-nity following BCG vaccination is similar and may last for 10–15 years.

      Although BCG vaccination has been used since 1921 and approximately 3 billion doses of vaccine have been given, the efficacy of the vaccine still continues to be controversial. Several field trials have been performed to assess the efficiency of the vaccine. The results have varied widely from 80% protection to a total absence of protection. However, two meta-analyses of the vaccine trials including the trials conducted in India have shown that BCG vaccine is effective against miliary and menin-geal tuberculosis.

 General health measures

General health measures include adequate nutrition, good housing, and health education.


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Microbiology and Immunology: Bacteriology: Mycobacterium tuberculosis : Prevention and Control for Mycobacterium tuberculosis Infections |


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