tuberculosis

Tuberculosis, or TB, is a slow-burning infection caused by a hardy bacterium that most often settles in the lungs. Think of it less like a sudden cold and more like a smouldering ember: it can sit quietly for years, then flare into a wasting illness with cough, fever, night sweats and weight loss. For most of human history it was a leading cause of death, once nicknamed “consumption” because it seemed to consume the body from within.

The disease spreads through the air when a person with active lung TB coughs, speaks or sneezes, releasing tiny droplet nuclei that others inhale. Once inside the lungs, the bacteria are engulfed by immune cells but can survive inside them, triggering a walled-off inflammatory reaction called a granuloma. In many people the immune system contains the infection indefinitely; in a minority it breaks down later and the bacteria multiply, producing contagious active disease.

TB exists on a spectrum from silent latent infection to florid active disease, and it can affect organs beyond the lungs, including lymph nodes, bones, kidneys and the lining of the brain. It is curable with a months-long combination of antibiotics, but drug resistance, poverty and HIV co-infection keep it among the world's deadliest infectious diseases. Diagnosis and treatment are handled by public-health and respiratory services; this entry is reference, not medical advice.