The World Health Organization (WHO) estimates that one-third of the world’s population is infected with TB. Many of those infected have latent TB and only a small percentage of those people will go on to develop the disease. In latent TB, a person will test positive for TB, but the bacteria they are infected with are inactive. Latent TB is not contagious and it causes no symptoms. In fact, only about 10 percent of people who are infected with TB ever get the disease! Unfortunately, overcrowding is a risk factor in urban areas, like Mumbai, India (a city of over 13 million people), making it easier for active TB to be passed from person to person.
Three-quarters of all active TB (TB that causes symptoms) is pulmonary TB (TB affecting the lungs). When the TB bacteria reach the lungs, they are confronted by macrophages (a type of white blood cell). The macrophages identify the bacteria as foreign, and then engulf and digest them. With most bacteria, macrophages are an effective means of defense, but the TB bacterium is able to resist being digested and can even multiply within the macrophage. The TB bacteria continue to reproduce until they literally burst the macrophage, causing the enzyme that should have destroyed them to be released into the lungs. This enzyme then attacks the lungs, damaging them and causing inflammation and more immune response. South African miners, like G.K. (shown here), often suffer from silicosis—a lung disease cause by breathing in silica dust while mining—which makes their TB even worse. Symptoms of pulmonary TB include cough, coughing up blood, chest pain, night sweats, weight loss, fever, chills, and loss of appetite.
TB can also affect other parts of the body, including the spine, brain, and kidneys. The symptoms of extrapulmonary TB (TB outside the lungs) vary depending on where the TB occurs. Both pulmonary and extrapulmonary TB can have devastating symptoms.
E.M. (shown here) was once a gold miner in South Africa, but now is very weak and relies on home health care workers to help him bathe, eat, and go to the doctor.