Tuberculosis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Tuberculosis (abbreviated as TB for Tubercle bacillus or Tuberculosis) is a common and deadly infectious disease caused by mycobacteria, mainly Mycobacterium tuberculosis. Tuberculosis most commonly attacks the lungs (as pulmonary TB) but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, joints and even the skin. Other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, and Mycobacterium microti can also cause tuberculosis, but these species do not usually infect healthy adults.[1]
Over one-third of the world's population has been exposed to the TB bacterium, and new infections occur at a rate of one per second.[2] Not everyone infected develops the full-blown disease; asymptomatic, latent TB infection is most common. However, one in ten latent infections will progress to active TB disease, which, if left untreated, kills more than half of its victims.
In 2004, mortality and morbidity statistics included 14.6 million chronic active TB cases, 8.9 million new cases, and 1.6 million deaths, mostly in developing countries.[2] In addition, a rising number of people in the developed world are contracting tuberculosis because their immune systems are compromised by immunosuppressive drugs, substance abuse, or HIV/AIDS.
The rise in HIV infections and the neglect of TB control programs have enabled a resurgence of tuberculosis.[3] The emergence of drug-resistant strains has also contributed to this new epidemic with, from 2000 to 2004, 20% of TB cases being resistant to standard treatments and 2% resistant to second-line drugs.[4] TB incidence varies widely, even in neighboring countries, apparently because of differences in health care systems.[5] The World Health Organization declared TB a global health emergency in 1993, and the Stop TB Partnership developed a Global Plan to Stop Tuberculosis aiming to save 14 million lives between 2006 and 2015.[6]
In the past, tuberculosis was called consumption, because it seemed to consume people from within, with a bloody cough, fever, pallor, and long relentless wasting. Other names included phthisis (Greek for consumption) and phthisis pulmonalis; scrofula (in adults), affecting the lymphatic system and resulting in swollen neck glands; tabes mesenterica, TB of the abdomen and lupus vulgaris, TB of the skin; wasting disease; white plague, because sufferers appear markedly pale; king's evil, because it was believed that a king's touch would heal scrofula; and Pott's disease, or gibbus of the spine and joints.[7][8] Miliary tuberculosis – now commonly known as disseminated TB– occurs when the infection invades the circulatory system resulting in lesions which have the appearance of millet seeds on x-ray.[7][9]
Historical Perspective
Tuberculosis has been present in humans since antiquity. The earliest unambiguous detection of Mycobacterium tuberculosis is in the remains of bison dated 18,000 years before the present.[10] However, whether tuberculosis originated in cattle and then transferred to humans, or diverged from a common ancestor, is currently unclear.[11]
Pathophysiology
About 90% of those infected with Mycobacterium tuberculosis have asymptomatic, latent TB infection (sometimes called LTBI), with only a 10% lifetime chance that a latent infection will progress to TB disease. However, if untreated, the death rate for these active TB cases is more than 50%.[12]
Epidemiology and Demographics
Tuberculosis, or TB is a bacterial infection that kills 3 million people worldwide, more people than any other infection in the world. Approximately one-third of the world is infected, and 15 million people in the US. Active tuberculosis kills 60% of the time if not treated, but treatment cures 90% of patients. Most people are infected with TB have latent TB. This means that the bacteria is controlled by the body's immune system. People with latent TB do not have symptoms and cannot transmit TB to other people. However, later if the infected person has a weakened immune system (AIDS, young children, elderly, sick with other diseases, etc.), the bacteria can break out leading to active TB, or TB disease.
Risk Factors
Progression from TB infection to TB disease occurs when the TB bacilli overcome the immune system defenses and begin to multiply.
Classification
The current clinical classification system for tuberculosis (TB) is based on the pathogenesis of the disease.
Causes
The primary cause of tuberculosis is Mycobacterium tuberculosis, an aerobic bacterium.
Diagnosis
History and Symptoms
Tuberculosis can be a difficult disease to diagnose, due mainly to the difficulty in culturing this slow-growing organism in the laboratory. A complete medical evaluation for TB must include a medical history, a chest x-ray, and a physical examination.
Physical Examination
A physical exam can provide valuable information about the patient’s overall condition and other factors that may affect how TB is treated, such as HIV infection or other illnesses.
Electrocardiogram
Patients can develop a pericardial effusion secondary to TB and this might be manifested as low voltage and tachycardia on an EKG.
Chest X-Ray
A chest X ray is one of the important diagnostic tools in tuberculosis. A chest radiograph may be used to rule out the possibility of pulmonary TB in a person who are symptomatic or had a positive reaction to a tuberculin test or QFT-G and no symptoms of disease. The findings on chest x ray can be divided into parenchymal and pleural. The early parenchmal findings can be infiltrates, and cavity. A healed tuberculotic lesion can present as fibrosis, and calcification. Pleural lesions in form of pleral effusion can also be seen. An advanced tuberculosis lesion can present as combination of these early lesions and termed as fibrocavitatory lesions.
Echocardiography or Ultrasound
Echocardiography or Ultrasound: Patients can develop a pericardial effusion secondary to TB.
Treatment
Medical Therapy
If their is a high probability of infection, presumptively treat the patient even if the stain is negative, while waiting for the culture results. The patient should be brought back in few weeks. Patients usually feel better a few weeks post-treatment. In the U.S., all TB is tested for drug resistance. Isoniazid (INH) resistant TB can be treated in same way as non-MDR TB.
Primary Prevention
Many countries use BCG vaccine as part of their TB control programs, especially for infants. This was the first vaccine for TB and developed at the Pasteur Institute in France between 1905 and 1921.[13] However, mass vaccination with BCG did not start until after World War II.[14] The protective efficacy of BCG for preventing serious forms of TB (e.g. meningitis) in children is greater than 80%; its protective efficacy for preventing pulmonary TB in adolescents and adults is variable, ranging from 0 to 80%.[15]
References
- ↑ Raviglione MC, O'Brien RJ (2004). "Tuberculosis". In Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL, Isselbacher KJ, eds. Harrison's Principles of Internal Medicine (16th ed. ed.). McGraw-Hill Professional. pp. 953–66. doi:10.1036/0071402357. ISBN 0071402357.
- ↑ 2.0 2.1 World Health Organization (WHO). Tuberculosis Fact sheet N°104 - Global and regional incidence. March 2006, Retrieved on 6 October 2006.
- ↑ Iademarco MF, Castro KG (2003). "Epidemiology of tuberculosis". Seminars in respiratory infections. 18 (4): 225–40. PMID 14679472.
- ↑ "Emergence of Mycobacterium tuberculosis with extensive resistance to second-line drugs—worldwide, 2000–2004". MMWR Morb Mortal Wkly Rep. 55 (11): 301–5. 2006. PMID 16557213.
- ↑ Sobero R, Peabody J (2006). "Tuberculosis control in Bolivia, Chile, Colombia and Peru: why does incidence vary so much between neighbors?". Int J Tuberc Lung Dis. 10 (11): 1292–5. PMID 17131791.
- ↑ World Health Organization (WHO). Stop TB Partnership. Retrieved on 3 October 2006.
- ↑ 7.0 7.1 Tuberculosis Encyclopedia Britannica, 11th ed.
- ↑ Rudy's List of Archaic Medical Terms English Glossary of Archaic Medical Terms, Diseases and Causes of Death. Accessed 09 Oct 06
- ↑ Disseminated tuberculosis NIH Medical Encyclopedia. Accessed 09 Oct 06
- ↑ Rothschild B, Martin L, Lev G, Bercovier H, Bar-Gal G, Greenblatt C, Donoghue H, Spigelman M, Brittain D (2001). "Mycobacterium tuberculosis complex DNA from an extinct bison dated 17,000 years before the present". Clin Infect Dis. 33 (3): 305–11. PMID 11438894.
- ↑ Pearce-Duvet J (2006). "The origin of human pathogens: evaluating the role of agriculture and domestic animals in the evolution of human disease". Biol Rev Camb Philos Soc. 81 (3): 369–82. PMID 16672105.
- ↑ Onyebujoh, Phillip and Rook, Graham A. W. World Health Organization Disease Watch: Focus: Tuberculosis. December 2004. Accessed 07 October 2006.
- ↑ Bonah C (2005). "The 'experimental stable' of the BCG vaccine: safety, efficacy, proof, and standards, 1921–1933". Stud Hist Philos Biol Biomed Sci. 36 (4): 696–721. PMID 16337557.
- ↑ Comstock G (1994). "The International Tuberculosis Campaign: a pioneering venture in mass vaccination and research". Clin Infect Dis. 19 (3): 528–40. PMID 7811874.
- ↑ Bannon M (1999). "BCG and tuberculosis". Arch Dis Child. 80 (1): 80–3. PMID 10325767.