What is TB?

Tuberculosis (TB) is a contagious disease that kills around 2 million people each year. One-third of the world’s population is currently infected with TB and someone is newly infected every few seconds.

What is the relationship between TB and HIV?

TB is the leading cause of death among HIV infected people; the WHO estimates that TB accounts for up to a third of AIDS deaths worldwide. When someone is infected with TB, the likelihood of them becoming sick with the disease is increased many times if they are also HIV positive.

What causes TB?

TB is caused by an organism called mycobacterium tuberculosis. These bacteria can attack any part of the body, but they most commonly attack the lungs. TB bacteria are very common in many resource-poor countries and in poor urban "pockets" of industrialised countries.

The spread of TB

A person can have active or inactive TB. Active TB or TB disease 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 TB 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 TB 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 TB. In some people TB bacteria remain inactive for a lifetime without becoming active. But in some other people the inactive TB may become active TB if their immune system becomes weakened – for example by HIV. People with inactive TB are also called TB carriers.

TB and HIV positive people

Because TB can spread through the air, the increase in active TB among people infected with both TB and HIV results in:

• more transmission of the TB bacteria
• more people with latent TB
• more TB disease in the whole population.

People with latent TB are increasingly becoming infected with HIV, and many more are developing active TB because HIV is weakening their 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.

People with advanced HIV infection are vulnerable to a wide range of infections and malignancies that are called "opportunistic infections" because they take advantage of the opportunity offered by a weakened immune system. TB is an HIV related opportunistic infection. A person that has both HIV and active TB has an AIDS-defining illness.

The HIV/AIDS epidemic is reviving an old problem in well resourced countries and greatly worsening an existing problem in resource poor countries. There are several important associations between epidemics of HIV and TB:

• TB is harder to diagnose in HIV positive people
• TB progresses faster in HIV-infected people
• TB in HIV positive people is more likely to be fatal if undiagnosed or left untreated
• TB occurs earlier in the course of HIV infection than other opportunistic infections
• TB is the only major AIDS-related opportunistic infection that poses a risk to HIV-negative people.

What are the symptoms of TB?

Symptoms of TB depend on where in the body the TB bacteria are growing. TB bacteria often grow in the lungs, causing pulmonary tuberculosis. Pulmonary TB may cause a bad cough that lasts longer than 2 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 TB diagnosed?

TB can be diagnosed by injecting a protein found in TB bacteria into the skin of an arm. If the skin reacts by swelling then the person is probably infected with TB. However, this method is not wholly reliable at detecting TB infections among HIV-infected people because their weakened immune systems often cannot mount a strong enough defence against the injected proteins to cause swelling. It also detects both active and latent TB, meaning the test is not very accurate at diagnosing active TB disease in people who live in areas where TB (and thus latent TB infection) is very common.

Diagnosis of TB 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+ 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 TB, 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 TB diagnosis is often based on symptoms.

How is TB treated?

Active TB disease can almost always be cured with a combination of antibiotics. The variety of treatments and drug options depend on the country you are in. A proper combination of anti-TB drugs provides both prevention and cure. Effective treatment quickly makes the person with TB non-contagious and therefore prevents further spread of TB. Achieving a cure takes about six to eight months of daily treatment.

Several drugs are needed to treat active TB. Taking several drugs does a better job of killing all of the bacteria and is more likely to prevent them from becoming resistant to the drugs. To ensure thorough treatment, it is often recommended that the patient takes his or her pills in the presence of someone who can supervise the therapy. This approach is called DOTS (directly observed treatment, short course). DOTS cures TB in 95% of cases, and a six-month supply of DOTS costs as little as $10 per person in some parts of the world.

Can TB be prevented?

There is a vaccine against TB called 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, and if given to HIV+ adults or children with very weak immune systems, it can occasionally cause disseminated BCG disease. This 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 TB 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.

TB 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 whereantiretroviral 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 TB and HIV at the same time. Some anti-HIV drugs can also interact with some TB drugs making the treatment more difficult. It is important that the TB 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, TB may be one of the earlier signs of HIV infection. Addressing TB offers the opportunity for early HIV intervention. Although treatment of TB 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.

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

When a strain of TB 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 classed as extreme drug resistant TB, or XDR-TB. Drug resistance usually arises when TB patients do not or cannot take their medicine as prescribed, and drug-resistant mutations of the TB 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 TB 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.

Note: This information is cross-posted and slightly adapted from AVERT.org in order to emphasize some aspects refering particulary to Moldova. For more details, visual adds, updated information and primary sources, please visit AVERT.org web page.

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