Tuberculosis is a chronic infectious disease caused by the bacteria Mycobacterium tuberculosis. Lungs are the most commonly affected organs however tuberculosis can affect almost any organ of the body namely, brain, joints, spine, uterus, liver, kidney, etc.
Tuberculosis may lead to either latent infection without any evident symptom or another form of tuberculosis which presents (active form) with symptoms. Active tuberculosis may also present with lung symptoms (pulmonary symptoms) or with symptoms due to involvement of other organs (extrapulmonary symptoms).
Common presenting symptoms of tuberculosis is mainly the lung symptoms namely cough with sputum tinged with blood along with other general symptoms like fever, night sweats, unexpected weight loss etc.
Causes
Mycobacterium tuberculosis, the causative bacteria of tuberculosis is an air borne bacteria. It spreads from the non treated persons with active symptoms of tuberculosis to other non infected persons through microscopic droplets of cough, sneeze or respiratory fluids as present in spits produced during laughing, singing etc of the infected person.
Despite the fact that the route of spread of infection is air, it is not easy to get infected with tuberculosis bacteria. The chance of being infected with tuberculosis increases when the non infected person comes in contact with the infected person on regular basis and not on one or two occasions. Hence getting the infection is easier when the infected person lives in the same house or works at the same office and the chance is not so high when the infected person is stranger.
Currently available anti tubercular drugs are so effective that most of the infected people with active disease become non contagious within 2 weeks of regular drug treatment.The immune system of the infected person’s body plays an important role in progression of the disease. In a healthy person the immune system of the body fights with tuberculosis bacteria and prevents in progression of the disease whereas if the immune system is not working properly then the tuberculosis bacteria can easily affect the different organs of the body leading to active form of the disease. Hence anyone with poor immune system activity is at increased risk of suffering from the active form of tuberculosis as the patients of HIV/AIDS.
 Multiple drug resistant tuberculosis (MDR-TB) is a serious problem. It occurs when a particular anti tubercular drug cannot kill all the infective bacteria, the surviving bacteria then propagates the disease in the affected person as well to other people. These bacteria gradually develop resistance to other standard antitubercular drugs. In most of the cases of MDR-TB resistance develops against isoniazid and rifampicin.
Risk factors
Tuberculosis infection can occur in any person although the chance of suffering from the active form of disease increases when
1. Inadequate functioning of the immune system: these are suffering from certain co-existent diseases namely HIV/AIDS, diabetes, renal failure (end stage), suffering from certain varieties of cancer, undergoing treatment for cancer, taking drugs (immunosuppressant drugs) in people with organ transplant, taking drugs for treatment of rheumatoid arthritis, Crohn’s disease, psoriasis etc, severe degree of malnutrition, young children , elderly people etc
2. Living or traveling to certain countries: tuberculosis is endemic in certain countries hence traveling or living in those countries increases the risk of suffering from tuberculosis. These countries are the Sub Saharan countries of Africa, India, China, Pakistan, Russia etc.
3. Poverty: one of the most common outcomes of poverty is malnutrition which leads to tends to suppress the normal immune response in an otherwise healthy person making him or her prone to suffer from active form of tuberculosis. Other problem with poverty is poor access to medical facility for early diagnosis and adequate treatment of tuberculosis.
4. Substance abuse like alcoholism or other illegal drug abuse may weaken the immune system and thus increases the risk of suffering from the active form of tuberculosis.
5. Living or working condition: people who live in contact with large number of people as in prisons, immigration centers, nursing homes are likely to come in with infected persons and subsequently are at in creased risk. Living in an unhygienic condition also increases the risk like those live at refugee camps or shelter houses are likely to suffer from the disease.
6. Health care workers are also at increased risk for  obvious reasons
Treatment
Drug therapy is the mainstay of treatment for tuberculosis. Treatment of tuberculosis requires longer time for about 6 to 9 months. The dose, duration, type of drugs etc depend upon the form of tuberculosis and the organs involved (pulmonary or extrapulmonary).
In case of latent tuberculosis treatment with one drug is enough whereas active form of the disease requires treatment with several drugs. The first line anti tubercular drugs are isoniazid, rifampicin, pyrazinamide, ethambutol and streptomycin.
In case of drug resistant tuberculosis (MDR-TB) fluroquinolines, aminogycocides like amikacin are used for 20 to 30 months.
Treatment with antitubercular drugs often lead to side-effects, some which are serious (like hepatitis) requiring changing the offending drug and some are not (passage of colored urine).
Another important thing in tuberculosis treatment is completing the entire course of treatment both in terms of duration and drugs. To facilitate adherence to the treatment a program known as directly observed treatment (DOT) is recommended.