What is tuberculosis?

• Tuberculosis (TB) is a disease caused by an organism called mycobacterium tuberculosis. The bacteria can attack any part of the body such as the brain, kidneys or the spine but they most commonly attack the lungs.

How is TB Spread?

• TB is contagious and it spreads from person to person through the air. A person can have active or inactive tuberculosis. Active TB means the bacteria are active in the body and the immune system is unable to stop them from causing illness. People with active TB in their lungs can pass the bacteria on to anyone they come into close contact with. When a person with active TB coughs, sneezes or spits, people nearby may breathe in the tuberculosis bacteria and become infected. Left untreated, each person with active TB will infect on average between 10 and 15 people every year.
• People can also be infected with tuberculosis that is not active in the body. Inactive TB infection is also called latent TB. If a person has latent TB, it means their body has been able to successfully fight the bacteria and stop them from causing illness. People who have latent TB do not feel sick, do not have symptoms and cannot spread tuberculosis. In some people tuberculosis bacteria remain inactive for a lifetime without becoming active. But in some people the inactive TB may become active TB if the immune system becomes weakened - for example by HIV.

What is the relationship between TB and HIV?

• TB kills up to half of all AIDS patients worldwide. People who are HIV-positive and infected with TB are up to 50 times more likely to develop active TB in their lifetime than people who are HIV-negative (UNAIDS,2007).

• People with latent TB are increasingly becoming infected with HIV, and many more are developing active TB because HIV is weakening the immune system. People who are co-infected with both HIV and latent TB have an up to 800 times greater risk of developing active TB disease and becoming infectious compared to people not infected with HIV.

• Many people living with HIV in developing countries develop TB as the first manifestation of AIDS. The two diseases represent a deadly combination, since they are more destructive together than either disease alone.
• People with advanced HIV infection are vulnerable to a wide range of infections because of the weakened immune system. TB progresses faster in people who are HIV-positive and TB in people who are HIV-positive is almost certain to be rapidly fatal if undiagnosed or left untreated.
• People infected with HIV and living with AIDS are at greater risk for developing MDR TB.

What are the symptoms of tuberculosis?

• Symptoms of tuberculosis depend on where in the body the TB bacteria are growing. Tuberculosis bacteria often grow in the lungs, causing pulmonary tuberculosis. Pulmonary tuberculosis may cause a bad cough that lasts longer than two weeks, pain in the chest and coughing up of blood or sputum. Other symptoms of TB disease include weakness or fatigue, weight loss, lack of appetite, chills, fever and night sweats.
• Inactive TB has no symptoms.

How is tuberculosis diagnosed?

• Diagnosis of tuberculosis in the lungs may be made using an X-ray or sputum test, but again, these may not give a clear indication of active TB infection in HIV positive people, because their immune systems are not strong enough to mount an inflammatory reaction against the bacteria. In cases of extra-pulmonary TB (where the disease is affecting organs other than the lungs), fluid or tissue samples may be tested.
• If there is doubt about the diagnosis of tuberculosis, a culture of TB bacteria can also be grown in a laboratory. However, this requires specialised and costly equipment and can take six to eight weeks to produce a result.
• If the necessary facilities are not available then the tuberculosis diagnosis is often based on symptoms.

How is tuberculosis treated?

• Almost every TB case is curable.
• People with TB are rarely hospitalised
• Standard treatment is 6 months – Longer
• A combination of 4 antibiotics for the first 2 months, and then 2 for the next 4 months
• Commonly used drugs are isoniazid, rimfampicin, pyrazinamide and ethambtul
• Non-infectious after two weeks treatment
• Adherence is crucial

Can tuberculosis be prevented?

• There is a vaccine against tuberculosis called Bacille Calmette-Guerin (BCG), but the vaccine is now very old (it was first used in the 1920s), and tests have found it to be very variable in its ability to protect people from infection in modern settings. When it does provide protection, this generally only lasts for around 15 years. The BCG can also cause false-positive readings on the tuberculin skin test. If given to HIV positive adults or children with very weak immune systems, the BCG can occasionally cause disseminated BCG disease, which is often fatal.
• A drug called isoniazid (INH) can be used as a preventative therapy for those who are at high risk of becoming infected with tuberculosis or for those who have inactive TB. People who have inactive TB but are not yet sick can take a course of isoniazid for several months to stop them developing active TB.
• The WHO recommends that HIV positive people who have latent TB (but definitely not active TB) should be offered isoniazid preventive therapy as needed.

Tuberculosis treatment and HIV

• It is vitally important for people with HIV to have treatment if they have active TB. This will cure them and prevent transmission to others. Even in settings where antiretroviral drugs are unavailable or inaccessible, it is crucial that the health system is able to offer HIV positive people the simple antibiotics needed for DOTS.
• For some people it can be difficult to take drugs for both tuberculosis and HIV at the same time. Some anti-HIV drugs can also interact with some tuberculosis drugs making the treatment more difficult. It is important that the tuberculosis treatment is taken regularly and exactly as the health care provider has advised. If the drugs are not taken regularly, the bacteria can become resistant to the drugs and this can be dangerous.
• As one of the first opportunistic infections to appear in HIV-infected people, tuberculosis may be one of the earlier signs of HIV infection. Addressing tuberculosis offers the opportunity for early HIV intervention. Although treatment of tuberculosis can improve the quality of life of HIV positive people and prolong their life, it cannot stop them from dying of AIDS. This is why access to antiretroviral treatment is also vitally important.

• Around the world, attempts are being made to improve collaboration between TB and HIV programmes. It is being proposed that everyone diagnosed with tuberculosis should be tested for HIV and vice-versa, and that treatment programmes should share facilities and expertise.

What are multi-drug resistant TB (MDR-TB) and extreme drug resistant TB (XDR-TB)?

• When a strain of tuberculosis bacteria is resistant to two or more 'first-line' antibiotic drugs it is called multi-drug resistant TB or MDR-TB. When it is resistant to three or more 'second-line' antibiotics as well, it is classified as extreme drug resistant TB, or XDR-TB. Drug resistance usually arises when tuberculosis patients do not or cannot take their medicine as prescribed, and drug-resistant mutations of the bacteria are allowed to replicate. People can also catch MDR- and XDR-TB from others.
• MDR-TB is a serious problem and is very difficult to treat. In normal first-line treatment, patients take the drugs isoniazid and rifampicin (the most effective tuberculosis drug available) plus two or three other first-line drugs for around six to eight months. If a person is resistant to isoniazid and rifampicin however, they are said to have MDR-TB, and will need to change to a regime containing newer and often less widely-available 'second-line' drugs. Treatment with second-line drugs can take a very long time, and is usually far more expensive than standard DOTS therapy because most of the drugs are still under patent.
• XDR-TB is even more serious. If someone has XDR-TB, it means they are not only resistant to isoniazid and rifampicin, but to three or more of the six available second-line drugs too. This can make it virtually impossible to formulate an effective treatment regime for them. Many people with XDR-TB will die before it is even realised that they have the extreme resistant strain.
• Although HIV infection does not of itself increase the chance of drug resistance occurring, both MDR-TB and XDR-TB are very serious threats to HIV positive people, whose weakened immune systems render them unlikely to fight off tuberculosis naturally (often the only hope for those with a resistant strain).

SOURCES

1. http://www.avert.org/tuberculosis.htm

2. http://www.who.int/tb/challenges/hiv/en/index.html

3.http://unaids.org/en/MediaCentre/PressMaterials/FeatureStory/20070320TB_Anywhere_WTBDay.asp

4. www.cdc.gov/tb