Tuberculosis

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.

Close relatives of the bacterium infect cattle (Mycobacterium bovis), swine and fowl (Mycobacterium avium). Infection occurs if the bacterium is ingested. Mycobacterium bovis in particular has been estimated to be responsible, for the period of the first half of the 20th century, for more losses among farm animals than all other infectious diseases combined.

Transmission of tuberculosis infection is usually from droplets coughed out by an infected person.

On the other hand, Mycobacterium bovis usually spreads through infected milk although it too can spread via droplets. Humans are susceptible to this bacterium that causes bovine tuberculosis.

Children up to 4 years of age are more at risk than adults. Tuberculous meningitis and miliary tuberculosis (so named because the lesions formed resemble millet seeds), a form of TB septicaemia, is more common in the young than the old.

TB is divided into pulmonary and extra-pulmonary TB. The most common form in adults is pulmonary tuberculosis, the 'classic' form of TB, in which the lungs are diseased. The disease begins gradually with coughing - later traces of blood are coughed up in the sputum (haemoptysis). Untreated, it leads to fever, weight-loss, and death. The term consumption arose because sufferers appear as if consumed by the disease.

After droplet infection, the MTB causes a local infection in the lung. After that, It moves to the hilar lymph nodes. The bacteria can later spread via the blood to all parts of the body. This is the reason that one can have TB in every organ, although pulmonary TB is most common. Other (extra-pulmonary) TB sites are lymph nodes, spinal column, kidneys and so on. In 90% of the infected people the body is able to defend itself well enough so that one won't get TB. In 1% the primary infection causes subsequent tuberculosis. The remaining 9% will get TB later, due to reactivation of dormant bacilli, usually within a few years after the infection. But this can happen even decades later. Chances of tuberculosis reactivating in the body is increased in cases of acquired immunodeficiency - whether due to AIDS, drugs or other causes. A depressed immune system also makes miliary tuberculosis more likely.

Sputum smears and cultures should be done for acid-fast bacili if the patient is producing sputum. If no sputum is being produced, a laryngeal swab, bronchoscopy or fine needle aspiration should be considered. Other mycobacteria are also AFB. One can distinguish these from "real" TB bacteria belonging to the Tuberculosis complex by means of a specific PCR or other gene probe.

The Mantoux test should be done in all cases of suspected tuberculosis, although the results must be interpreted carefully. Tuberculin units are injected intradermally (into the skin) and read 48 to 72 hours later. Tuberculin is the purified proteins of the M. tuberculosis bacteria; thus a patient who has been exposed to the bacteria is expected to mount an immune response in the skin containing the bacterial proteins. An induration (hardened spot of skin) of more than 10mm to 10 Mantoux units is considered a positive result, indicating TB infection. A negative test does not exclude active tuberculosis, especially if the test was done within 6 to 8 weeks of acquiring the infection, if the infection is overwhelming or if the patient is immunocompromised.

There is no relation between the effectiveness of the BCG vaccine and a positive Mantoux test. After BCG vaccination testing with a Mantoux test is not useful and unnecesary. One BCG is enough; revaccination is not useful. A previous BCG vaccination sometimes give false-positive results.This makes the Mantoux test less useful in BCG vaccinated people. In order to improve the Mantoux test, several other tests are being developed. A promising one is a (blood) test that looks at the reaction of T-lymfocytes to the antigens ESAT6 and CFP10.

Tuberculosis should be suspected when a persistent respiratory illness in an otherwise healthy individual does not respond to regular antibiotics (such as penicillin, or amoxicillin).

When someone is diagnosed with tuberculosis, all his/her close contacts should be screened for TB with a Mantoux test and/or a chest x-ray. In Britain the obsolete Heaf test is still used.

Why four drugs? If only one drug is given, what ends up happening is that all the bacteria sensitive to that drug are killed and three months later, the patient will be infected with progeny of the bacteria that were resistant to that particular drug. Rifampicin and isoniazid are bactericidal agents that kill the bacteria, pyrizinamide acts well against the intracellular bacteria which are dormant inside macrophages and other cells and ethambutol is a bacteriostatic agent that inhibits bacterial proliferation while the other drugs kill off the TB. Rifampin is the drug that gives the best "sterilization", this means that it will kill dormant bacteria very well in order to lower the number of relapses after a succesful treatment.

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 was in immunizing against tuberculosis. Developed from attenuated bovine strain tuberculosis by Albert Calmette and Camille Guerin in 1906 - 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 WW 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 per cent of those who entered were dead within five years (1908).

In Europe, deaths from TB fell from 500 out of 100,000 Europeans in 1850, to 50 out of 100,000 by 1950. Improvements in public health were impacting 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 defaulters(?) 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 heroine of Puccini's opera La Bohème suffers from tuberculosis (a theme carried over in the modern film adaptation Moulin Rouge).

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.

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.

• List of famous tuberculosis victims
• Scrofula
• Christmas Seals
• American Lung Association

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