Tuberculosis is an infection with the bacterium Mycobacterium tuberculosis, which most commonly affects the lungs (pulmonary TB) but can also affect the central nervous system (meningitis), lymphatic system, circulatory system (miliary TB), genitourinary system, bones and joints.
Other names for the disease are:
- TB (short for tuberculosis)
- Consumption (TB seemed to consume people from within with its symptoms of bloody cough, fever, pallor, and long relentless wasting)
- Wasting disease
- White plague (TB sufferers appeared markedly pale)
- Phthisis (Greek for consumption) and phthisis pulmonalis
- Scrofula (swollen neck glands)
- King's evil (so called because it was believed that a king's touch would heal scrofula)
- Pott's disease of the spine
- Miliary TB (x-ray lesions look like millet seeds)
- Tabes mesenterica (TB of the abdomen)
- Lupus vulgaris (the common wolf - TB of the skin)
Tuberculosis is the most common major infectious disease today, infecting two billion people or one-third of the world's population, with nine million new cases of active disease annually, resulting in two million deaths, mostly in developing countries.
Most of those infected (90 percent) have asymptomatic latent TB infection (LTBI). There is a 10 percent lifetime chance that LTBI will progress to active TB disease which, if left untreated, will kill more than 50 percent of its victims. TB is one of the top three infectious killing diseases in the world: HIV/AIDS kills 3 million people each year, TB kills 2 million, and malaria kills 1 million.
The neglect of TB control programs, HIV/AIDS, and immigration has caused a resurgence of tuberculosis. Multiple drug resistant strains of TB (MDR-TB) is increasing. The World Health Organization declared TB a global health emergency in 1993.
The cause of tuberculosis, Mycobacterium tuberculosis (MTB), is a slow-growing aerobic bacterium that divides every 16 to 20 hours. This is extremely slow compared to other bacteria, which tend to have division times measured in minutes (among the fastest growing bacteria is a strain of E. coli that can divide roughly every 20 minutes). It is not classified as either Gram-positive or Gram-negative because it does not have the chemical characteristics of either, although it contains peptidoglycan in their cell wall. If a Gram stain is performed, it stains very weakly Gram-positive or not at all. It is a small rod-like bacillus which can withstand weak disinfectants and can survive in a dry state for weeks but, spontaneously, can only grow within a host organism (in vitro culture of M. tuberculosis took a long time to be achieved, but is nowadays a normal laboratory procedure).
MTB is identified microscopically by its staining characteristics: it retains certain stains after being treated with acidic solution, and is thus classified as an "acid-fast bacillus" or "AFB". In the most common staining technique, the Ziehl-Neelsen stain, AFB are stained a bright red which stands out clearly against a blue background. Acid-fast bacilli can also be visualized by fluorescent microscopy, and by auramine-rhodamine stain.
The M. tuberculosis complex includes 3 other mycobacteria which can cause tuberculosis: M. bovis, M. africanum, and M. microti. The first two are very rare causes of disease and the last one does not cause human disease.
Nontuberculous mycobacteria (NTM) are other mycobacteria (besides M. leprae which causes leprosy) which may cause pulmonary disease resembling TB, lymphadenitis, skin disease, or disseminated disease. These include Mycobacterium avium, M. kansasii, and others.
TB is spread through water droplets which are expelled when persons with infectious TB disease cough, sneeze, speak, or sing. Close contacts (people with prolonged, frequent, or intense contact) are at highest risk of becoming infected (typically 22 percent infection rate but everything is possible, even up to 100%). Others at risk include foreign-born from areas where TB is common, residents and employees of high-risk congregate settings, health care workers who serve high-risk clients, medically underserved, low-income populations, high-risk racial or ethnic minority populations, children exposed to adults in high-risk categories, and people who inject illicit drugs.
Transmission can only occur from people with active TB disease (not latent TB infection).
The probability of transmission depends upon: infectiousness of the person with TB (quantity expelled), environment of exposure, duration of exposure, and virulence of the organism.
The chain of transmission can be stopped by isolating patients with active disease and starting effective anti-tuberculous therapy.
While only 10 percent of TB infection progresses to TB disease, if untreated the death rate is 50 percent.
TB infection begins when TB bacilli reach the pulmonary alveoli, from which they may spread to local lymph nodes, and then through the bloodstream to the more distant tissues and organs where TB disease is likely to develop: lung apices, peripheral lymph nodes, kidneys, brain, and bone.
The bacterium causes a type IV immune hypersensitivity response. T-lymphocytes secrete cytokine and recruit and activate macrophage. These macrophages form spherical aggregates in the tissues called granulomas. A granuloma when viewed under the microscope by histology shows a central zone of large macrophagic cells surrounded by a zone of T-lymphocytes. Some of the macrophages fuse to form multinucleate giant cells termed Langerhans Giant cells. Tuberculosis is therefore classed as one of the granulomatous inflammatory conditions.
The granulomas in tuberculosis are called tubercles, or tuberculous nodules. They can be seen in tissues by the naked eye as small white spots 1-2mm in size.
This type IV immune response can kill some bacteria. Bacteria can also survive where they live within the macrophagic cells. If the affected patient has a strong immune system and is well nourished, it is likely that the immune response will eliminate bacteria and the tubercle heals by formation of a scar. Usually the immune system is able to halt the multiplication of TB bacilli, preventing further spread in about 90 percent of cases. However if a person has a weak immune system or is poorly nourished bacteria are not eliminated and proliferate. The tubercles enlarge and there is local tissue destruction.
Another feature of the granulomas of tuberculosis is the development of cell death, also called necrosis, in the centre of tubercles. To the naked eye this has the texture of soft white cheese and was termed caseous necrosis.
If TB bacteria gain entry to the blood stream from an area of tissue damage they spread through the body and set up myriad foci of infection, all appearing as tiny white tubercles in the tissues. This is called miliary tuberculosis and has a high case fatality.
In many patients the infection waxes and wanes. Tissue destruction and necrosis are balanced by healing and fibrosis. Affected tissue is replaced by scarring and cavities filled with cheese-like white necrotic material. In the lung some of these cavities are in continuity with the air passages bronchi. This material may therefore be coughed up. It contains living bacteria and can pass on infection.
Treatment with appropriate antibiotics kills bacteria and allows healing to take place. Affected areas are eventually replaced by scar tissue.
In those people in whom TB bacilli overcome the immune system defenses and begin to multiply, there is progression from TB infection to TB disease. This may occur soon after infection (primary TB disease – 1 to 5 percent) or many years after infection (post primary TB, secondary TB, reactivation TB disease of dormant bacilli – 5 to 9 percent).
About five percent of infected persons will develop TB disease in the first two years, and another five percent will develop disease later in life. In all, about 10 percent of infected persons with normal immune systems will develop TB disease in their lifetime.
Some medical conditions increase the risk of progression to TB disease. In HIV infected persons with TB infection, the risk increases to 10 percent each year instead of 10 percent over a lifetime. Other such conditions include drug injection (mainly because of the life style of IV Drug users), substance abuse, recent TB infection (within two years) or history of inadequately treated TB, chest X-ray suggestive of previous TB (fibrotic lesions and nodules), diabetes mellitus, silicosis, prolonged corticosteroid therapy and other immunosuppressive therapy, head and neck cancers, hematologic and reticuloendothelial diseases (leukemia and Hodgkin's disease), end-stage renal disease, intestinal bypass or gastrectomy, chronic malabsorption syndromes, or low body weight (10 percent or more below the ideal).
Some drugs, including rheumatoid arthritis drugs that work by blocking tumor necrosis factor-alpha (an inflammation-causing cytokine), may raise the risk of contracting tuberculosis or causing a latent infection to become active.
TB disease most commonly affects the lungs (75 percent or more), where it is called pulmonary TB. Symptoms include a productive, prolonged cough of more than three weeks duration, chest pain, and hemoptysis. Systemic symptoms include fever, chills, night sweats, appetite loss, weight loss, and easy fatigability. The term consumption arose because sufferers appeared as if they were "consumed" from within by the disease. People from Asian and African descent may have more often lymph node TB than Caucasians.
Extrapulmonary sites include the pleura, central nervous system (meningitis), lymphatic system (scrofula of the neck), genitourinary system, and bones and joints (Pott's disease of the spine). An especially serious form is "disseminated", or "miliary" TB, so named because the lung lesions so-formed resemble millet seeds on x-ray. These are more common in immunosuppressed persons and in young children. Pulmonary TB may co-exist with extrapulmonary TB.
Drug-resistant TB is transmitted in the same way as drug-susceptible TB. Primary resistance develops in persons initially infected with resistant organisms. Secondary resistance (acquired resistance) develops during TB therapy due to inadequate treatment regimen, not taking the prescribed regimen appropriately or using low quality medication.
A complete medical evaluation for TB includes a medical history, a physical examination, a tuberculin skin test, a chest X-ray, and microbiologic smears and cultures.
- See: tuberculosis diagnosis, tuberculosis radiology
Persons with TB infection (class 2 or class 4 TB), but who do not have TB disease (class 3 or class 5 TB), cannot spread the infection to other people. TB infection in a person who does not have TB disease is not considered a case of TB and is often referred to as latent TB infection (LTBI). This distinction is important because treatment options will be different for a person who has LTBI instead of active TB disease.
- See: tuberculosis treatment
Prevention and control efforts include three priority strategies:
- identifying and treating all persons who have TB disease
- finding and evaluating persons who have been in contact with TB patients to determine whether they have TB infection or disease, and treating them appropriately, and
- testing high-risk groups for TB infection to identify candidates for treatment of latent infection and to ensure the completion of treatment.
In tropical areas where the incidence of atypical mycobacteria is high, exposure to nontuberculous mycobacteria gives some protection against TB.
Many countries use BCG vaccine as part of their TB control programs, especially for infants. The protective efficacy of BCG for preventing serious forms of TB (e.g. meningitis) in children is high (greater than 80 percent). However, the protective efficacy for preventing pulmonary TB in adolescents and adults is variable, from 0 to 80 percent. In the United Kingdom, children aged 10-14 are typically immunized during school.
The effectiveness of BCG is much lower than in areas where mycobacteria are much less prevalent. In the USA, BCG vaccine is not routinely recommended except for selected persons who meet specific criteria:
- Infants or children with negative skin-test result who are continually exposed to untreated or ineffectively treated patients or will be continually exposed to multidrug-resistant TB.
- Healthcare workers considered on individual basis in settings in which high percentage of MDR-TB patients has been found, transmission of MDR-TB is likely, and TB control precautions have been implemented and not successful.
BCG vaccine and tuberculin skin test
Tuberculin skin testing is not contraindicated for BCG-vaccinated persons.
Latent TB infection (LTBI) diagnosis and treatment for LTBI is considered for any BCG-vaccinated person whose skin test is 10 mm or greater, if any of these circumstances are present:
- Was contact of another person with infectious TB
- Was born or has resided in a high TB prevalence country
- Is continually exposed to populations where TB prevalence is high.
The first recombinant tuberculosis vaccine entered clinical trials in the United States in 2004 sponsored by the National Institute of Allergy and Infectious Diseases (NIAID). 
A 2005 study showed that a DNA TB vaccine given with conventional chemotherapy can accelerate the disappearance of bacteria as well as protecting against re-infection in mice; it may take four to five years to be available in humans. PMID 15690060.
Because of the limitations of current vaccines, researchers and policymakers are promoting new economic models of vaccine development including prizes, tax incentives and advance market commitments.
Tuberculosis can be carried by many mammals. Domesticated species, such as cats and dogs, are generally free of tuberculosis, but wild animals may carry it (among other possible diseases). As a result, many places have regulations restricting the ownership of novelty pets, possibly including such partially-domesticated species as pet skunks; for example, the Canadian province of Quebec forbids the owning of hedgehogs as pets, and the American state of California forbids the ownership of pet gerbils. The strictness of such restrictions generally depends on the public health policies adopted for fighting tuberculosis.
Tuberculosis has been present in humans since antiquity, as the origins of the disease are in the first domestication of cattle (which also gave humanity viral poxes). Skeletal remains show prehistoric humans (4000 BC) had TB and tubercular decay has been found in the spines of Egyptian mummies from 3000-2400 BC. There were references to TB in India around 2000 BC and TB was present in The Americas from about 2000 BC
Phthisis is a Greek term for consumption. Around 460 BC, Hippocrates identified phthisis as the most widespread disease of the times which was almost always fatal.
Due to the variety of its symptoms, TB was not identified as a unified disease until the 1820s and was not named tuberculosis until 1839 by J.L. Schoenlein.
First TB sanatorium opened in 1859 in Poland; later, in 1885 in the United States.
The bacillus-causing tuberculosis, Mycobacterium tuberculosis, was described on March 24, 1882 by Robert Koch. He received the Nobel Prize in physiology or medicine for this discovery in 1905. Koch did not believe that bovine (cattle) and human tuberculosis were similar, which held back the recognition of infected milk as a source of infection. Later, this source was eliminated by pasteurization. Koch announced a glycerine extract of the tubercle bacilli as a "remedy" for tuberculosis in 1890, calling it tuberculin. It was not effective, but was later adapted by von Pirquet for a test for pre-symptomatic tuberculosis.
The first genuine success in immunizing against tuberculosis developed from attenuated bovine strain tuberculosis by Albert Calmette and Camille Guerin in 1906 was BCG (Bacillus of Calmette and Guerin). It was first used on humans on July 18, 1921 in France, although national arrogance prevented its widespread use in either the USA, Great Britain, or Germany until after World War II.
Tuberculosis caused the most widespread public concern in the 19th and early 20th centuries as the endemic disease of the urban poor. In 1815 England one in four deaths were of consumption; by 1918 one in six deaths in France were still caused by TB. After the establishment in the 1880s that the disease was contagious, TB was made a notifiable disease in Britain; there were campaigns to stop spitting in public places, and the infected poor were "encouraged" to enter sanatoria that rather resembled prisons. Whatever the purported benefits of the fresh air and labour in the sanatoria, 75% of those who entered were dead within five years (1908).
In the United States, concern about the spread of tuberculosis played a role in the movement to prohibit public spitting except into spittoons.
In Europe, deaths from TB fell from 500 out of 100,000 in 1850 to 50 out of 100,000 by 1950. Improvements in public health were reducing tuberculosis even before the arrival of antibiotics, although the disease's significance was still such that when the Medical Research Council was formed in Britain in 1913 its first project was tuberculosis.
It was not until 1946 with the development of the antibiotic streptomycin that treatment rather than prevention became a possibility. Prior to then only surgical intervention was possible as supposed treatment (other than sanatoria), including the pneumothorax technique: collapsing an infected lung to "rest" it and allow lesions to heal, which was an accomplished technique but was of little benefit and was discontinued after 1946.
Hopes that the disease could be completely eliminated have been dashed since the rise of drug-resistant strains in the 1980s. For example, TB cases in Britain, numbering around 50,000 in 1955, had fallen to around 5,500 in 1987, but in 2001 there were over 7,000 confirmed cases. Due to the elimination of public health facilities in New York in the 1970s, there was a resurgence in the 1980s. The number of those failing to complete their course of drugs was very high. NY had to cope with more than 20,000 "unnecessary" TB-patients with many multi-drug resistant strains (i.e., resistant to, at least, both Rifampin and Isoniazid). The resurgence of tuberculosis resulted in the declaration of a global health emergency by the World Health Organization in 1993.
In 2003, by disabling a set of genes, researchers accidentally created a more lethal and rapidly reproducing strain of tuberculosis bacteria.
Christmas Seals was started in 1904 in Denmark as a way to raise money for tuberculosis programs. It expanded to the United States and Canada in 1907-08 to help the National Tuberculosis Association, later called the American Lung Association.
Tuberculosis in art, literature, history and film
It has been speculated that the real-life ubiquity of illness and death due to tuberculosis affected the portrayal of these issues in European art and literature as well as history.
David Brainerd (born: April 20, 1718, died: October 9, 1747) only lived 29 years. His diary has been published and reflects his reliance upon God's faithfulness amidst his battle with consumption. Brainard's diary has proven historically very influential, particularly to the modern Christian missionary movement. He was a close friend of Theologian and Pastor Jonathan Edwards in New England. More information about Brainerd's life can be found detailed by contemporary pastor/theologian John Piper here, with Brainerd's diary being found here .
The Life and Death of Mr. Badman (1680) by John Bunyan - "Yet the captain of all these men of death that came against him to take him away, was the consumption, for it was that that brought him down to the grave."
The pale, "haunted" appearance of tuberculosis sufferers has been seen as an influence on the works of Edgar Allan Poe and in vampire tales. In recent years, this aesthetic has been revived by the "Goth" subculture.
The heroine, Mimi, of Puccini's opera La Bohème suffers from tuberculosis (a theme carried over in the modern film adaptation Moulin Rouge!). Violetta, heroine of Verdi's La Traviata also dies of the disease.
In Jane Eyre by Charlotte Bronte, Jane's best friend in school dies of consumption. It is indicative of the horrible conditions of these types of schools in the 1800s.
In Sylvia Plath's novel The Bell Jar, the protagonist Esther's boyfriend Buddy Willard suffers from tuberculosis, much to her liking.
In Nicholas Nickleby, by Charles Dickens, Nickleby's faithful companion Smike is beset by tuberculosis.
Extensively, in The Magic Mountain, by Thomas Mann, where a three week visit to a sanitarium turns into a seven year sabbatical.
Tuberculosis patients were frequent characters in 19th century Russian literature, and even inspired a character type; the consumptive nihilist, examples of which include Bazarov from Ivan Turgenev's Fathers and Sons, Katerina Ivanovna from Dostoyevsky's Crime and Punishment, and Kirillov from Fyodor Dostoevsky's Demons (aka The Possessed).
The hospitalized mother in the anime movie My Neighbor Totoro is thought to be suffering from tuberculosis (her ailment is not specifically named in the film, but tuberculosis is cited in the film's novelization). This is an autobiographical reference to the fact that writer/director Hayao Miyazaki's own mother spent several years of his childhood hospitalized with TB.
The Sick Child (1886) by Edvard Munch, portrait of his deceased sister Sophie who died of TB at 16. 
In Hocus Pocus by Kurt Vonnegut, the protagonist contracts TB later in his lifetime.
In "A Long Days Journey Into Night" by Eugene O'Neill character Edmund Tyrone is sick with consumption.
In the film "Moulin Rouge!", Satine (the beautiful courtesan) is dying from the disease.
In the Australian novel Seven Little Australians , Judy becomes consumptive after walking from the Blue Mountains to her home.
Core Curriculum on Tuberculosis: What the Clinician Should Know, 4th edition (2000). Division of Tuberculosis Elimination, Centers for Disease Control and Prevention (CDC). (Internet versionupdated Aug 2003).
- Joint Tuberculosis Committee of the British Thoracic Society. Control and prevention of tuberculosis in the United Kingdom: Code of Practice 2000. Thorax 2000;55:887-901 (fulltext).
- Thomas Dormandy (1999). The White Death: A History of Tuberculosis. ISBN 0814719279 HB - ISBN 1852853328 PB
Mountains Beyond Mountains: The Quest of Dr. Paul Farmer, a Man Who Would Cure the World. Tracy Kidder, Random House 2000. ISBN 0812973011. A nonfiction account of treating TB in Haiti, Peru, and elsewhere.
- Ha SJ, Jeon BY, Youn JI, Kim SC, Cho SN, Sung YC. Protective effect of DNA vaccine during chemotherapy on reactivation and reinfection of Mycobacterium tuberculosis. Gene Ther. 2005 Feb 03; [Epub ahead of print] PMID 15690060