Tuberculosis

Tuberculosis, often called TB, is a highly contagious disease.

It is caused by a specific bacterium named Mycobacterium tuberculosis (MTB). While TB most commonly attacks the lungs, it can also infect other parts of the body. The disease exists in two distinct states: latent and active. Latent tuberculosis means the bacteria are in the body, but the person shows no symptoms. People with latent TB cannot spread the disease to others. However, a small number of these infections progress into active disease. If active TB is not treated, it can be fatal.

Active tuberculosis spreads through the air between people. When a person with active TB in their lungs coughs, speaks, sneezes, or spits, the bacteria travel in tiny droplets.

This allows the infection to move from one person to another. People with weakened immune systems are at a higher risk of a latent infection becoming active. To find the bacteria, doctors use two principal tests. One is the interferon-gamma release assay (IGRA), which uses a blood sample. The other is the tuberculin skin test. Prevention relies on screening high-risk groups, such as those living or working near people with active TB. Vaccination with the bacillus Calmette-Guérin (BCG) vaccine is also a key tool for prevention.

History shows that tuberculosis has been present in humans since ancient times.

Skeletal remains show that prehistoric humans had TB as early as 4000 BC. Researchers have even found tubercular decay in the spines of Egyptian mummies from 3000 to 2400 BC. In the 1800s, the disease was known as "consumption." During this era, it was responsible for an estimated 25% of all deaths in Europe. In England, one in four deaths in 1815 was due to consumption. In France, TB caused one in six deaths by 1918. These high numbers caused widespread public concern, especially among the urban poor.

Scientists worked for centuries to understand the cause of the disease. In 1720, Benjamin Marten suggested that microbes caused consumption and spread through close contact. In 1819, René Laennec identified that tubercles in the lungs were a primary characteristic of the disease. Later, Jean Antoine Villemin demonstrated in 1865 that TB could be transmitted between humans and animals. The most significant breakthrough came on March 24, 1882.

On this day, Robert Koch identified and described the Mycobacterium tuberculosis bacillus. Koch later won the Nobel Prize in Physiology or Medicine for this discovery. Today, the world marks World Tuberculosis Day every March 24 to honor his work.

Treating tuberculosis has changed drastically over time. Before the mid-1900s, doctors had few options. They sometimes used a surgical technique called pneumothorax to collapse an infected lung. This was intended to let the lung rest so lesions could heal.

In 1946, the development of the antibiotic streptomycin made a cure a reality. Modern treatment requires using multiple antibiotics over a long period. However, a serious challenge has emerged since the 1980s: antibiotic resistance. Some strains of the bacteria have learned to survive standard medicines.

There are different levels of drug resistance in tuberculosis. Primary drug resistance occurs when a person catches TB that is already resistant to drugs. Secondary or acquired resistance happens when a person's treatment is inadequate or they do not follow the prescribed regimen. Multi-drug resistant TB (MDR-TB) is defined by resistance to two main drugs: rifampicin and isoniazid.

Even more serious is extensively drug-resistant TB (XDR-TB), which resists rifampicin and other specific drugs. Treating MDR-TB is much harder. It requires second-line drugs that are more toxic and expensive. In the UK, treating MDR-TB can cost ten times more than standard treatment.

Despite medical progress, TB remains a major global health issue. It is estimated that approximately 2 billion people, or one quarter of the world's population, have latent TB.

In 2024, TB is estimated to have newly infected 10.7 million people. It also caused an estimated 1.23 million deaths that year. Because of these numbers, TB is currently the leading cause of death from an infectious disease. Managing the disease requires constant work in vaccination, sanitation, and the development of new medicines to fight resistant strains.