Facts about Mycobacterium tuberculosis

 

1. According to Global Tuberculosis report of world health organization (WHO) estimated 1.5 million people died from tuberculosis (TB) globally in 2020, latest global TB report 2021 released on 14 Oct according to this report India accounted for 41% of total global drop of 1.3 million cases.  

- In 2019 7.1 million cases globally reported 

- In 2020 5.8 million cases globally reported by WHO    

2. You can imagine how one breath can make you sick like we all  have faced fear of Corona Virus ,tuberculosis is also a infectious disease spread by air transmission from people with active pulmonary TB.

3. Need to be conscious about your Immune system, because people with weakened immune system have a much greater risk of falling ill from TB.

4. A person living with HIV is about 20 times more likely to develop active TB.

5. About 1/3 population of the world is infected with tuberculosis but latently, they have no symptoms.

6. Only small proportion of those infected will become sick with TB have symptoms of severe cough, fever ,night sweat, weight loss , fatigue and loss of appetite.

7. This is also one of the reasons why HIV is severe having TB ,which induced the immune system it leads to the activation of T cells, in turn produce more HIV virions than quiescent T cells.

8. Few little efforts can stop the spread of TB like -

        - Always cover the mouth and nose when sneezing or coughing.  

        - Do not spit on the ground.

        - Maintain personal hygiene.  

        - Avoid smoking.

        - If you have symptoms ,tell your doctor so it can be tested and treated if required.

9. Pulmonary TB can spread from lungs to different body organs through hematogenous route.  

10. TB is a curable disease which can be treated with a standard 6 month course of 4 anti tubercular drugs which are provided by health care workers under Revised National Tuberculosis Control Programme (RNTCP) ,currently RNTCP name changed into NTEP ( National tuberculosis Eliminating programme) that uses the DOTS (Directly Observed Treatment, Short course chemotherapy ) strategy of  Indian Government. 

 Lab diagnosis-

Specimen collection-

-In pulmonary tuberculosis, sputum is collected in a clean mouthed container.

-Two sputum samples are recommended under NTEP , spot sample and early morning sample.

-In children, gastric aspirate may be collected.

Direct Microscopy-

- Sputum smear microscopy is the most commonly used for diagnosis of pulmonary TB.

- ZN staining technique is used to observe red colored long Acid fast bacilli against the blue background.

- In 2009 the WHO recommended that the conventional Bright field microscopy using ZN stain should be replaced by the more sensitive fluorescent light emitting diode (LED) microscopy. Mostly it is using in high burden countries, it is expensive, even today it is not used in every laboratories.  

-Thus at the present time , ZN microscopy most widely used in the diagnosis of TB.  

  Grading of the AFB smear-

- If  No bacilli seen in 100 fields so it gives result Negative 

- If 1-9 Bacilli seen in 100 fields, it gives result Scanty.

- If 10-99 Bacilli seen in 100 fields ,it gives result (1+).

- If 1-10 Bacilli seen per fields and 50 field to be examined ,it gives result (2+). 

-If Greater than 10 Bacilli seen per field and 20 field to be examined ,it gives result (3+). 

Culture-

Solid media-

it can be also culture on Lowenstein Jensen media (LJ media ) ,incubate it at 37°C and observe every 7th day . Decontamination procedure of sputum with adding 5% NaOH solution is important to do before inoculation of sample on culture media ( LJ media). .Observe at least for 4-6 weeks for result declaration negative or positive. Culture positive Appears rough, tough and buff white colored colonies. 

Automated Culture Methods-Several automated culture have been developed in last decade. They have many advantages over the conventional LJ culture. CBNAAT, BACTEC MGIT 960 system, True- NAT, Gene-Xpert/RIF  and  BACTEC Alert etc. 

BACTEC MGIT 960 system:- Digested and decontaminated sputum samples were inoculated into a mycobacteria growth indicator tube (MGIT) with modified Middle brook 7H9 broth (liquid media) supplemented with OADC (Oleic acid, Albumin, Dextrose and Catalase) enrichment and PANTA (Polymyxin B, amphotericin B, Nalidixic acid, trimethoprim, and Azlocillin ) antibiotic mixture.

 Positive- tube contains approximately 105 - 106 colony-forming units per milliliter (CFU/mL),      detected by fluorescence analysis.

Negative- Culture declared negative with no visible signs of positivity, removed after 45 days from the instrument.

Advantages- 

1.Detects growth faster (2-3 weeks),

2. Automated and continuous monitoring of growth, 

3. Less contamination issues.

Disadvantages-

It is expensive. 

CBNAAT-( cartridge based nucleic acid amplification):-

- A semi automated molecular assay Gene-Xpert in India is known as CBNAAT which detects MTB ribosomal RNA or DNA directly from sputum specimens, both the acid-fast bacilli (AFB) smear-positive and AFB smear-negative.

- In July it was announced that as a new test which could detect resistance to both first line and second line drugs. 

- Clinicians can find out in 90 minutes which drugs a patient is resistant to and prescribe the correct treatment, It's very helpful to detect MDR/XDR-TB.

- True-Nat was recommended by the WHO in January2020 as a alternative to Gene-Xpert.

Advantages- 

its Reliable in comparison of conventional sputum microscopy and speed to getting a result when compared with the culture test. 

   

Disadvantages-

1. The shelf life of the cartridges is 18 months only,

2. Continuous electricity supply is required, 

3. Costly test,

BACTEC Alert-

based on principle of colorimetric detection of pH change in the medium which occurs due to CO2 liberated by the growth of Mycobacterium tuberculosis.

  

Treatment- 

In case of active TB disease you will be treated with anti tubercular medication for a period of 6-12 months. Most common treatment for active TB is Isoniazid, Rifampin, Pyrazinamide and Ethmbutol ,these are first line drugs of TB.

Second line drugs- Kanamycin, Capreomycin , and Amikacin are injectable  Bedaquiline and Delamanid are new drugs.

Third line drugs- Rifabutin, Mcarolides ,Linozolid.

  

In case of tuberculosis co-infection with HIV, need to treat tuberculosis first ,because TB disease is spreads by airborne respiratory droplets ( coughs and sneezes) and saliva from one person to other person and HIV is transmitted through hematogenous route.