Popularly about the disease

Tuberculosis is an infectious (contagious) disease, the causative agent of which is Mycobacterium tuberculosis (Mykobacterium tuberculosis, often referred to as a bacillus or bacillus Kochii in honour of the scientist who discovered this causative microorganism in 1882). This disease is mainly an airborne disease transmitted from an infected person to a healthy person. In the majority of cases tuberculosis primarily affects the lungs; however, this disease can occur in any organ such as kidneys, spine, brain, lymph nodes, intestines, skin, genitals, etc..
One can become infected with tuberculosis by inhaling air which contains the causative agent of the disease - Mycobacterium tuberculosis.
This microorganism is like no other microbes. Its unique character, in the first place, is that it is resistant to the environment. Mycobacterium tuberculosis is resistant to cold and short-term exposure to high temperatures. It is able to be preserved in the environment for a long time: in dust, soil, snow, ice. The known cases bear evidence to the fact that Egyptian mummies which had the signs of tuberculosis of bones, contained a living bacillus Kochii.
Another feature of Mycobacterium tuberculosis is that it is quite old (TB spine damage was found during the study of a human being from the Neolithic age - about 5000 BC) and is well adapted to humans as well as humans are adapted to it. It easily gets into a human body; however, very often it does not cause a disease, but enters into "peaceful" relations with the immune system of the body that controls its presence in the body. In such a "peaceful" relationship bacillus Kochii continues living in a "dormant" state in the organisms of the majority of infected people, but the disease does not develop throughout their lives. Only 10% of people infected with bacillus Kochii develop the disease.
Who are these people? These are mainly people with a weakened immune system due to many diseases. First and foremost, due to HIV infection that affects the immune system, as well as other diseases that considerably weaken it: diabetes mellitus, diseases which lay a person under a necessity to take drugs that suppress the immune system (when getting treatment for cancer, rheumatosis, prevention of transplant rejection).
In addition to the mentioned categories of people who run increased risk of being taken ill with this disease, tuberculosis is likely to be taken by people whose immune system is weakened due to excessive overload and inanition of the body. Such states are incidental to fatigue, excessive labour and constant stress situations, malnutrition (including debilitating hypocaloric diets), misuse of alcohol, drugs, tobacco, etc.
Even people with strong immunity can be taken ill with tuberculosis in case of massive ingress of the causative agent into the body. Such situations typically arise due to close contact with a person who is sick with active TB through coughing, sneezing, talking or inhaling a considerable amount of air that is infected with Mycobacterium tuberculosis. The introduction of infection may occur in indoor area that is poorly ventilated, in the room where a TBC patient is or was situated, as well as in public transport, shops, cinemas and any crowded public places.
Remember that the risk of contamination with TB in the open is lower than indoors!

Animated video "All the truth about tuberculosis. Main symptoms" (ukr, 45 sec.)