Tuberculosis

Tuberculosis, MTB, or TB (short for tubercle bacillus) is a common, and in many cases lethal, infectious disease
caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have an active MTB
infection cough, sneeze, or otherwise transmit their saliva through the air. Most infections in humans result in an
asymptomatic, latent infection, and about one in ten latent infections eventually progress to active disease, which, if
left untreated, kills more than 50% of those infected.
The classic symptoms are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss (the last
giving rise to the formerly prevalent colloquial term “consumption”). Infection of other organs causes a wide range
of symptoms. Diagnosis relies on radiology (commonly chest X-rays), a tuberculin skin test, blood tests, as well as
microscopic examination and microbiological culture of bodily fluids. Treatment is difficult and requires long
courses of multiple antibiotics. Social contacts are also screened and treated if necessary. Antibiotic resistance is a
growing problem in (extensively) multi-drug-resistant tuberculosis. Prevention relies on screening programs and
vaccination, usually with Bacillus Calmette-Guérin vaccine.
One third of the world’s population is thought to have been infected with M. tuberculosis, and new infections occur at a rate of about one per second.In 2007 there were an estimated 13.7 million chronic active cases, and in 2010 8.8 million new cases, and 1.45 million deaths, mostly in developing countries. The absolute number of tuberculosis cases has been decreasing since 2006 and new cases since 2002. In addition, more people in the developing world contract tuberculosis because their immune systems are more likely to be compromised due to
higher rates of AIDS.

The distribution of tuberculosis is not uniform across the globe; about 80% of the
population in many Asian and African countries test positive in tuberculin tests, while only 5–10% of the U.S.
population test positive.

Risk factors
There are a number factors that make people more susceptible to TB infections. Worldwide the most important of these is HIV with co-infection present in about 13% of cases. This is a particular problem in Sub-Saharan Africa
where rates of HIV are high. Tuberculosis is closely linked to both overcrowding and malnutrition making it
one of the principal diseases of poverty.
Chronic lung disease is a risk factor with smoking more than 20
cigarettes a day increasing the risk by two to four times and silicosis increasing the risk about 30 fold. Other disease states that increase the risk of developing tuberculosis include alcoholism and diabetes mellitus (threefold increase). Certain medications such as corticosteroids and Infliximab (an anti-αTNF monoclonal antibody) are
becoming increasingly important risk factors, especially in the developed world.There is also a genetic susceptibility for which overall importance is still undefined.

Transmission
When people with active pulmonary TB cough, sneeze, speak, sing, or
spit, they expel infectious aerosol droplets 0.5 to 5 µm in diameter. A
single sneeze can release up to 40,000 droplets.[44] Each one of these
droplets may transmit the disease, since the infectious dose of
tuberculosis is very low and inhaling fewer than ten bacteria may cause
an infection.

Prevention
Tuberculosis prevention and control efforts primarily rely on the vaccination of infants and the detection and appropriate treatment of active cases.The World Health Organization has achieved some success with improved
treatment success and a small decrease in case numbers.
Vaccines
The only currently available vaccine as of 2021 is Bacillus Calmette-Guérin (BCG) which while effective against disseminated disease in childhood, confers inconsistent protection against pulmonary disease. It is the most
widely used vaccine worldwide with more than 90% of children vaccinated. However the immunity that it induces, decreases after about ten years. As tuberculosis is uncommon in most of Canada, the United Kingdom
and the United States, BCG is only administered to people at high risk. Part of the reason against the use of vaccine is that it makes the tuberculin skin test falsely positive and thus of no use in screening. A number of new vaccines are in development.
Public health
The World Health Organization (WHO) declared TB a global health emergency in 1993 and in 2006 the Stop TB Partnership developed a Global Plan to Stop Tuberculosis that aims to save 14 million lives between its launch and
2015. A number of targets that they have set are not likely to be achieved by 2015 due to the increase in HIV
associated tuberculosis and multi-drug resistant tuberculosis.
Treatment
Treatment for TB uses antibiotics to kill the bacteria. Effective TB treatment is difficult, due to the unusual structure and chemical composition of the mycobacterial cell wall, which makes many antibiotics ineffective and hinders the entry of drugs. The two antibiotics most commonly used are isoniazid and rifampicin and treatments can be
prolonged. Latent TB treatment usually uses a single antibiotic, while active TB disease is best treated with
combinations of several antibiotics, to reduce the risk of the bacteria developing antibiotic resistance. People with latent infections are treated to prevent them from progressing to active TB disease later in life.

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