by Dr Paul Saunderson
Tuberculosis – usually known as TB – was one of the most feared of all diseases in the 19th century.
In the past 100 years TB has become less of a problem in many developed countries for two main reasons. The first was the understanding of how the disease spread – this began with the work of Robert Koch in 1882. Through this knowledge, public health measures were introduced to reduce the spread of the disease. The second reason is the improvement in general living standards, with better housing, nutrition and sanitation.
However, in developing countries the situation is very different. The risk of infection from TB remains as high as it was in the past. About 1.7 billion people – one third of the world’s population – are infected with TB.
TB is still one of the most feared diseases and kills around three million people each year.
The only available vaccine, BCG, can protect children but it does not prevent the spread of TB. Into this already depressing situation, the effects of the HIV pandemic are likely to be devastating.
HIV infection weakens the body’s ability to fight off infection. As numbers of HIV-infected people rise around the world, a rapid increase in the numbers of TB patients is expected. TB programmes in many countries have little effect now – how will they cope when numbers of patients rise rapidly? In this article we will look at some of the possible solutions to a huge and growing problem.
How does TB spread?
TB spreads by tiny bacteria – the TB bacilli. When a person with active TB coughs, TB bacilli pass into the air. Infection is most likely in closed and crowded rooms – usually in home or work situations. Sputum (spit) can also carry infection. Cattle can also be infected with TB and TB bacilli may be carried in milk which is not pasteurised.
Prevent the spread of TB by encouraging people not to cough or spit indoors. Discourage the habit of spitting on the ground.
Where TB is common, half of the population is infected by the time they are adults. People often do not know they are infected – there are usually no symptoms. In most cases the body’s defenses are strong enough to prevent the spread of the TB bacilli and they simply remain in the lungs and lymph nodes. Only 10% of infected people will eventually go on to develop active TB.
There are two kinds of active TB…
- PULMONARY TB (TB of the lungs)
- NON-PULMONARY TB (TB of other parts of the body)
Over half of the people who develop active TB will develop TB in the lungs (pulmonary TB). This is most common because TB bacilli usually first enter the body through the lungs as the person breathes them in. This is the infectious kind of TB. These people spread the disease to others, especially children within their own household. One person with pulmonary TB will infect 20–28 other people on average, before they either die or recover. 2–3 of those infected will develop TB. Without treatment, 60–70% of those infected will die within five years.
This leads to a stable situation or cycle (see below), with the number of deaths being equalled by the number of new cases of TB. This was the case in much of sub-Saharan Africa until the HIV pandemic arrived.
Effects of the HIV pandemic on the TB cycle
HIV infection reduces the body’s ability to resist disease and infection. Diseases that a healthy body could normally resist, are able to develop. TB bacilli are very common and quick to take advantage of the weakening of the body’s resistance.
When people already infected with the TB bacilli become HIV-infected, more than half (instead of just 10% normally) will develop active TB. This leads to an increase in the risk of infection and a breakdown of the stable cycle.
A rapid increase in the number of TB patients is expected. Current programmes are unlikely to be able to cope. What hope is there for TB control as the number of HIV-infected people continues to rise rapidly? There are several major problems for TB control programmes…
- There are now too many patients to be treated in hospital for the first two months. (After this time the person will not infect others.)
- Many TB patients cannot reach a hospital based programme, for economic and geographic reasons.
- TB is now associated with AIDS in many people’s minds – patients are increasingly isolated and rejected.
- Treatment may need to be taken for longer if someone has HIV-damaged immunity.
To view The stable TB cycle, click here (PDF, 251K)