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Introduction to TB – What is TB?, latent TB & TB disease, symptoms, diagnosis & treatment

Introduction to TB

This page gives a brief introduction to TB, including what it is, latent TB & TB disease, and  some facts about tests, drugs & treatment.

What is TB?

TB is a bacterial disease which in humans is usually caused by an organism called Mycobacterium tuberculosis (M. tuberculosis). TB is an abbreviation of the word Tuberculosis and is how people usually refer to the disease.

Bovine TB is a disease caused by similar bacteria called Mycobacterium bovis (M. bovis). Bovine TB mainly affects cattle but can also affect humans. Most of the information on this website refers to TB in humans caused by M. tuberculosis.

Just a few years ago it was believed that TB was an old disease, and that it was no longer a problem in humans. But now because of such issues as drug resistance and HIV, it has become a major problem again.

Latent TB

The bacteria that usually cause TB in humans, usually affect the lungs, but can affect other parts of the body. If you are infected with the bacteria you won’t necessarily become sick, because you can have either latent TB or TB disease.1Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/default.htm

Any introduction to TB must explain the difference between latent TB & TB disease

Any introduction to TB must explain the difference between latent TB and TB disease

Latent TB occurs when a person has the bacteria within their body, but the bacteria are present in very small numbers.  They are kept under control by the body’s immune system and do not cause any symptoms. People with latent TB do not feel sick and do not have any symptoms. It is usually only known that someone has latent TB because they have had a test, such as the TB skin test. People with latent TB are not infectious and cannot pass the bacteria on to other people.2Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/default.htm

TB disease

TB disease is what happens when a person has latent TB and then becomes sick. Sometimes this is known as having active TB or TB disease. Most people with latent TB never become sick. Overall about 5 to 10% of people with latent TB, who do not receive treatment for it, will become sick at some time in their lives.3“Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/risk.htm

Some people become sick soon after they have become infected, before their immune system (the part of the body that fights diseases) can fight the bacteria. Other people don’t get sick at first but they get sick years later when their immune system becomes weak for another reason. This can be because they have an infection, such as infection with HIV, or some other health problem.

Some people are known to have a higher risk of becoming ill.4“Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings 2005”, CDC, 5 www.cdc.gov/tb/publications/guidelines/infectioncontrol.htm

These include:

  • Infants and children aged less than 4 years
  • People infected within the previous two years
  • People infected with HIV
  • People who have certain illnesses or conditions which affect their immune system, such as people with diabetes, and people with chronic renal failure.

How do you get TB?

High magnification of TB bacteria that cause TB disease

High magnification of TB bacteria that cause TB disease

You get TB by inhaling TB bacteria that are in the air. The bacteria spread through the air from one person to another. Bacteria get released into the air by some person who is already infected with them. When a person with TB of the lungs or throat coughs, sneezes, sings or talks, droplets containing the bacteria are released into the air. That is why people who think they may be infectious, may often hold something over their mouth when they are near to other people. People working in a health clinic may for this reason sometimes wear a mask.

People are not equally infectious. Generally it is only people with TB of the throat or lungs who are infectious.5“Guidelines for the Investigation of Contacts of Persons with Infectious Tuberculosis”, CDC, www.cdcnpin.org/scripts/tb/cdc.asp Also, the most important factor is whether someone is on effective treatment. TB treatment dramatically reduces the number of infectious droplets released by a person. The strength of a person’s cough can also affect the number of droplets released.

How long do TB bacteria stay alive?

The bacteria can sometimes stay alive in the air for a few hours, especially in small places with no fresh air. Fresh air and sunlight make it harder for the bacteria to stay alive. The fresh air scatters the bacteria and the sunlight kills them.6“Get the Facts About TB Disease”, CDC www.cdc.gov/tb/publications/pamphlets/default.htm

Why do some people become infected when others don’t?

It is not known why some people who are exposed to the bacteria become infected when other people don’t. The chance of becoming infected  depends mainly on the amount of infectious droplets in the air, and the length of exposure to an infectious person. The closer the infectious person is, and the longer the time of exposure, the higher the risk is of being infected.7“Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings 2005”, CDC, 5 www.cdc.gov/tb/publications/guidelines/infectioncontrol.htm

The bacteria are not transmitted:

  • through food and water,
  • or by kissing,
  • or by skin contact such as shaking hands,
  • or by touching a toilet seat,
  • or by sharing a toothbrush.

What are the symptoms?

The symptoms depend on which area of the body has been infected. If someone has pulmonary disease, which is TB in the lungs, then they may have a bad cough that lasts longer than two weeks. They may also have pain in their chest and they may cough up blood or phlegm from deep inside their lungs. Other symptoms of TB include weakness or fatigue, weight loss, lack of appetite, chills, fever and night sweats.8“Get the Facts About TB Disease”, CDC www.cdc.gov/tb/publications/pamphlets/default.htm

Diagnosing TB

It is very difficult to diagnose TB by a person’s symptoms on their own. This is because some other diseases have the same symptoms.

A diagnosis is usually only certain when there is definite evidence of TB bacteria. Some of the TB tests used for diagnosis look directly for the bacteria. Others such as the chest X-ray look for the effect of the bacteria on the person suspected of having TB. Tests for diagnosis include the TB skin test, sputum microscopy, the culture test as well as the new Genexpert test.

Major problems with the tests are the lack of accuracy as well as the time they take. With newer tests a major issue is the cost.

Treatment

Streptomycin, a drug used to treat TB

Streptomycin, a drug used to treat TB

TB can usually be cured. The treatment usually consists of a combination of TB drugs that must be taken for at least six months. But the treatment will only be successful if the drugs are taken exactly as required for the entire length of time.

Some of the drugs have very severe side effects and are very difficult to take for such a long period of time. This is why there is such an urgent need for new TB drugs to be developed. Two new drugs are delamand and bedaquiline but they are only for the treatment of MDR TB. There is lots more and this is only an introduction to TB treatment.

Drug resistant TB

If someone has drug resistant TB it means that the bacteria in their body won’t be affected by certain drugs that they are resistant to. The drugs just won’t work. There are two main reasons why people develop it. It can be because the person doesn’t take their drugs properly. It can also be that the bacteria that they are infected with, have come from someone who has already got drug resistant TB. Being drug sensitive is the opposite of being drug resistant.

If someone has drug resistant TB then they must change drugs. But they mustn’t have just one new drug. They need to have several new drugs and for it to be believed that they will all be effective. Drug susceptibility testing which is available in many countries, and is very important, provides information about which drugs a person is resistant to.

TB prevention

A major part of the prevention of TB is to stop the spread of the bacteria from one adult to another. This is done by firstly finding the adults who have TB. Then providing them with effective treatment means that they are no longer infectious and they will also recover from being sick. There is a vaccine, the BCG vaccine, but it is used for children as it doesn’t seem to prevent the disease in adults.

Sometimes it is believed that education about TB only needs to involve people who already have the disease. But there is a need to also educate the general public. This is firstly to ensure that people know how TB is transmitted and indeed not transmitted, and to also reduce the stigma surrounding the disease. It can also help to ensure that people with TB come forward for testing and treatment as soon as possible.

References

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1. Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/default.htm
2. Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/default.htm
3. “Basic TB Facts”, CDC www.cdc.gov/TB/topic/basics/risk.htm
4. “Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings 2005”, CDC, 5 www.cdc.gov/tb/publications/guidelines/infectioncontrol.htm
5. “Guidelines for the Investigation of Contacts of Persons with Infectious Tuberculosis”, CDC, www.cdcnpin.org/scripts/tb/cdc.asp
6. “Get the Facts About TB Disease”, CDC www.cdc.gov/tb/publications/pamphlets/default.htm
7. “Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings 2005”, CDC, 5 www.cdc.gov/tb/publications/guidelines/infectioncontrol.htm
8. “Get the Facts About TB Disease”, CDC www.cdc.gov/tb/publications/pamphlets/default.htm