To the naked eye, this has the texture of soft, white cheese and is termed caseous necrosis.If TB bacteria gain entry to the blood stream from an area of damaged tissue, they can spread throughout the body and set up many foci of infection, all appearing as tiny, white tubercles in the tissues.Bacteria inside the granuloma can become dormant, resulting in latent infection.Another feature of the granulomas is the development of abnormal cell death (necrosis) in the center of tubercles.About 10% of latent infections progress to active disease which, if left untreated, kills about half of those infected.The classic symptoms of active TB are a chronic cough with blood-containing sputum, fever, night sweats, and weight loss.
Macrophages and dendritic cells in the granulomas are unable to present antigen to lymphocytes; thus the immune response is suppressed.
When it spreads to the bones, it is also known as "osseous tuberculosis", MTB can withstand weak disinfectants and survive in a dry state for weeks. NTM cause neither TB nor leprosy, but they do cause pulmonary diseases that resemble TB.
In nature, the bacterium can grow only within the cells of a host organism, but M. Using histological stains on expectorated samples from phlegm (also called "sputum"), scientists can identify MTB under a microscope. Those at high risk thus include: people who inject illicit drugs, inhabitants and employees of locales where vulnerable people gather (e.g.
tuberculosis strain, the level of immunity in the uninfected person, and others.
The cascade of person-to-person spread can be circumvented by segregating those with active ("overt") TB and putting them on anti-TB drug regimens.
The number of new cases each year has decreased since 2000.