Tuberculosis (TB)

What is it?

– Tuberculosis has been around since ancient times and is still one of the world’s major scourges. One in every three people in the world are permanently infected, and TB caused an estimated 1.8 million deaths in 2015, the vast majority of them in the developing world. – There are many reasons for this terrible toll. TB is a disease of poverty that thrives when people are malnourished or lack good healthcare. Smoking increases the risk. The only vaccine doesn’t protect very well, and treatments are cumbersome and hard to complete. The HIV/Aids pandemic has dramatically worsened the problems; so has the rise of antibiotic resistance.

– The main cause of TB is a bacterium called Mycobacterium tuberculosis, which only infects humans.

Mycobacterium tuberculosis, the main bacterium that causes TB, seen through a scanning electron microscope. Credit: CDC

 

What are the symptoms?

– More than two billion people are estimated to be infected with TB without any symptoms; this is called a ‘latent’ infection. In approximately 10% of patients, TB will go from latent to active at some point, which means they get sick; why and how that happens is not clear exactly.

– TB is primarily a lung disease. The most characteristic symptom is a chronic cough, producing sputum and sometimes blood. Other symptoms include chest pain, fever, chills, night sweats, and a loss of appetite and weight. In up to 20% of cases (up to 50% of those infected with HIV) TB affects other organs and tissues as well, such as the lymphatic system, bones, joints, the nervous system, and the urogenital tract, leading to a wide range of additional symptoms.

– When untreated, active TB kills around half of all patients.

 

How does it spread?

– People with latent TB can’t transmit TB. People with active TB produce tiny droplets full of bacteria when they cough or sneeze, and even when they speak or sing, that float through the air and can infect people nearby.  The chances of transmission depend on many factors, including how long someone was in contact with the patient and how close they came, the bacterial strain, and the immune status of the non-infected person.

– People on treatment for TB usually stop being contagious after a few weeks.

– TB occurs around the world, but 95% of cases are in low- and middle income countries. Asia accounted for 51% of the new cases in 2015, according to WHO, and Africa for 26%. Six countries (India, Indonesia, China, Nigeria, Pakistan, and South Africa) together have 60% of all cases.

TB is a global problem but most cases and deaths occur in Asia and Africa. Credit: WHO

 

 

How is it treated?

– TB is curable, but it’s not easy. The standard regimen is a combination of four different antibiotics taken over a period of six months. Patients often start feeling better long before the treatment ends, and sometimes abandon the therapy as a result. It’s important they finish the treatment, however, to make sure the infection is completely eliminated. Stopping early can also contribute to drug resistance in the TB bacterium.

– Drug resistance is a big problem with TB. There were about 480,000 cases of so-called multi-drug resistant (MDR) TB in 2015 (roughly 5% of all cases), in which the microbe is resistant to isoniazid and rifampicin, the two most important drugs. MDR-patients can be treated with an alternative regime, but these ‘second-line’ drugs are more expensive, have more side effects, and patients need to take them for up to two years.

– Even more difficult is ‘extensively drug-resistant’ TB, or XDR-TB, in which the bacteria don’t respond to second-line drugs either. At this point, some cases become impossible to treat and the patient is at high risk of dying.

 

What do TB and HIV have to do with each other?

TB and HIV are dual epidemics that exacerbate each other. People infected with HIV, whose immune systems are weakened, are 20-30 times more likely to advance from latent TB to active TB. Meanwhile, there’s evidence that having TB makes it more difficult to control HIV. One in three people with HIV worldwide actually dies from TB. That’s why WHO recommends that the fight against these two diseases should be integrated, especially in Africa.

 

How can TB be prevented?

– TB is a difficult disease to prevent. There is a vaccine, called  Bacillus Calmette-Guérin, or BCG, which as been around since 1921. Around 90% of children worldwide get BCG soon after birth, making it one of the most widely used vaccines. But it’s not very good. BCG reduces both the risk of infection as well as the risk of developing active TB once you are infected by roughly half. But it is much less effective in some countries than in others, for reasons that are not clear. Moreover, its effects start to wane after 10 years; BCG does not protect adults against TB.

– Another important way of preventing the disease is finding people who have active TB early and putting them on treatment as soon as possible, so that they are no longer a danger to others, and taking care of them using proper infection control. People with latent TB can be treated as well to prevent them from moving to active TB.

A TB detection and treatment unit at work in Lima, Peru. Credit: PAHO

 

What’s the outlook?

– The battle against TB is tough, but progress is possible and is being made. Between 2000 and 2015, the number of deaths has declined by 22%. China has made impressive inroads thanks to increased funding for basic health services in the wake of the 2003 SARS outbreak.

– In 2014, WHO adopted the “End TB Strategy” to make massive gains worldwide. The plan aim to reduce TB deaths by 90% and to cut new cases by 80% between 2015 and 2030. Ending the TB epidemic by 2030 is also one of the health targets in Sustainable Development Goals. This will require a tremendous effort by many countries, however, and billions of dollars.

– Scientists are working on new, better vaccines–which would make prevention much easier–and new antibiotics that can reduce the treatment time.

Contact a tuberculosis expert.

Resources

WHO’s starting page for TB, with links to more information about almost every aspect of the disease.

The Global tuberculosis report, an annual update on the disease and the efforts to control it.

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